HHH-11544 - Joins over type variable defined relations is non-deterministic

Fix single table inheritance issues and improve polymorphic join condition

hibernate-core/src/main/java/org/hibernate/engine/internal/JoinSequence.java

@@ -129,7 +129,28 @@ public class JoinSequence {
 			String alias,
 			JoinType joinType,
 			String[] referencingKey) throws MappingException {
-		joins.add( new Join( factory, associationType, alias, joinType, referencingKey ) );
+		joins.add( new Join( factory, associationType, alias, joinType, new String[][] { referencingKey } ) );
+		return this;
+	}
+
+	/**
+	 * Add a join to this sequence
+	 *
+	 * @param associationType The type of the association representing the join
+	 * @param alias The RHS alias for the join
+	 * @param joinType The type of join (INNER, etc)
+	 * @param referencingKeys The LHS columns for the join condition
+	 *
+	 * @return The Join memento
+	 *
+	 * @throws MappingException Generally indicates a problem resolving the associationType to a {@link Joinable}
+	 */
+	public JoinSequence addJoin(
+			AssociationType associationType,
+			String alias,
+			JoinType joinType,
+			String[][] referencingKeys) throws MappingException {
+		joins.add( new Join( factory, associationType, alias, joinType, referencingKeys ) );
 		return this;
 	}
 
@@ -242,8 +263,7 @@ public class JoinSequence {
 							join.getAlias(),
 							join.getLHSColumns(),
 							JoinHelper.getRHSColumnNames( join.getAssociationType(), factory ),
-							join.joinType,
+							join.joinType
-							""
 					);
 				}
 				addSubclassJoins(
@@ -263,17 +283,28 @@ public class JoinSequence {
 			joinFragment.addFromFragmentString( " on " );
 
 			final String rhsAlias = first.getAlias();
-			final String[] lhsColumns = first.getLHSColumns();
+			final String[][] lhsColumns = first.getLHSColumns();
 			final String[] rhsColumns = JoinHelper.getRHSColumnNames( first.getAssociationType(), factory );
-			for ( int j=0; j < lhsColumns.length; j++) {
+			if ( lhsColumns.length > 1 ) {
-				joinFragment.addFromFragmentString( lhsColumns[j] );
+				joinFragment.addFromFragmentString( "(" );
-				joinFragment.addFromFragmentString( "=" );
+			}
-				joinFragment.addFromFragmentString( rhsAlias );
+			for ( int i = 0; i < lhsColumns.length; i++ ) {
-				joinFragment.addFromFragmentString( "." );
+				for ( int j = 0; j < lhsColumns[i].length; j++ ) {
-				joinFragment.addFromFragmentString( rhsColumns[j] );
+					joinFragment.addFromFragmentString( lhsColumns[i][j] );
-				if ( j < lhsColumns.length - 1 ) {
+					joinFragment.addFromFragmentString( "=" );
-					joinFragment.addFromFragmentString( " and " );
+					joinFragment.addFromFragmentString( rhsAlias );
+					joinFragment.addFromFragmentString( "." );
+					joinFragment.addFromFragmentString( rhsColumns[j] );
+					if ( j < lhsColumns[i].length - 1 ) {
+						joinFragment.addFromFragmentString( " and " );
+					}
 				}
+				if ( i < lhsColumns.length - 1 ) {
+					joinFragment.addFromFragmentString( " or " );
+				}
+			}
+			if ( lhsColumns.length > 1 ) {
+				joinFragment.addFromFragmentString( ")" );
 			}
 
 			joinFragment.addFromFragmentString( " and " );
@@ -568,14 +599,14 @@ public class JoinSequence {
 		private final Joinable joinable;
 		private final JoinType joinType;
 		private final String alias;
-		private final String[] lhsColumns;
+		private final String[][] lhsColumns;
 
 		Join(
 				SessionFactoryImplementor factory,
 				AssociationType associationType,
 				String alias,
 				JoinType joinType,
-				String[] lhsColumns) throws MappingException {
+				String[][] lhsColumns) throws MappingException {
 			this.associationType = associationType;
 			this.joinable = associationType.getAssociatedJoinable( factory );
 			this.alias = alias;
@@ -599,7 +630,7 @@ public class JoinSequence {
 			return joinType;
 		}
 
-		public String[] getLHSColumns() {
+		public String[][] getLHSColumns() {
 			return lhsColumns;
 		}
 

hibernate-core/src/main/java/org/hibernate/hql/internal/ast/tree/DotNode.java

@@ -6,6 +6,11 @@
  */
 package org.hibernate.hql.internal.ast.tree;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Set;
+
 import org.hibernate.QueryException;
 import org.hibernate.engine.internal.JoinSequence;
 import org.hibernate.hql.internal.CollectionProperties;
@@ -16,6 +21,7 @@ import org.hibernate.internal.CoreLogging;
 import org.hibernate.internal.CoreMessageLogger;
 import org.hibernate.internal.log.DeprecationLogger;
 import org.hibernate.internal.util.StringHelper;
+import org.hibernate.internal.util.collections.ArrayHelper;
 import org.hibernate.persister.collection.QueryableCollection;
 import org.hibernate.persister.entity.AbstractEntityPersister;
 import org.hibernate.persister.entity.EntityPersister;
@@ -483,11 +489,6 @@ public class DotNode extends FromReferenceNode implements DisplayableNode, Selec
 		boolean useFoundFromElement = found && canReuse( classAlias, elem );
 
 		if ( !useFoundFromElement ) {
-			// If this is an implied join in a from element, then use the impled join type which is part of the
-			// tree parser's state (set by the gramamar actions).
-			JoinSequence joinSequence = getSessionFactoryHelper()
-					.createJoinSequence( impliedJoin, propertyType, tableAlias, joinType, joinColumns );
-
 			// If the lhs of the join is a "component join", we need to go back to the
 			// first non-component-join as the origin to properly link aliases and
 			// join columns
@@ -501,6 +502,27 @@ public class DotNode extends FromReferenceNode implements DisplayableNode, Selec
 
 			String role = lhsFromElement.getClassName() + "." + propertyName;
 
+			JoinSequence joinSequence;
+
+			if ( joinColumns.length == 0 ) {
+				// When no columns are available, this is a special join that involves multiple subtypes
+				String lhsTableAlias = getLhs().getFromElement().getTableAlias();
+
+				AbstractEntityPersister persister = (AbstractEntityPersister) lhsFromElement.getEntityPersister();
+
+				String[][] polyJoinColumns = persister.getPolymorphicJoinColumns(lhsTableAlias, propertyPath);
+
+				// Special join sequence that uses the poly join columns
+				joinSequence = getSessionFactoryHelper()
+						.createJoinSequence( impliedJoin, propertyType, tableAlias, joinType, polyJoinColumns );
+			}
+			else {
+				// If this is an implied join in a from element, then use the implied join type which is part of the
+				// tree parser's state (set by the grammar actions).
+				joinSequence = getSessionFactoryHelper()
+						.createJoinSequence( impliedJoin, propertyType, tableAlias, joinType, joinColumns );
+			}
+
 			FromElementFactory factory = new FromElementFactory(
 					currentFromClause,
 					lhsFromElement,

hibernate-core/src/main/java/org/hibernate/hql/internal/ast/util/SessionFactoryHelper.java

@@ -273,6 +273,24 @@ public class SessionFactoryHelper {
 		return joinSequence;
 	}
 
+	/**
+	 * Generate a join sequence representing the given association type.
+	 *
+	 * @param implicit Should implicit joins (theta-style) or explicit joins (ANSI-style) be rendered
+	 * @param associationType The type representing the thing to be joined into.
+	 * @param tableAlias The table alias to use in qualifying the join conditions
+	 * @param joinType The type of join to render (inner, outer, etc);  see {@link org.hibernate.sql.JoinFragment}
+	 * @param columns The columns making up the condition of the join.
+	 *
+	 * @return The generated join sequence.
+	 */
+	public JoinSequence createJoinSequence(boolean implicit, AssociationType associationType, String tableAlias, JoinType joinType, String[][] columns) {
+		JoinSequence joinSequence = createJoinSequence();
+		joinSequence.setUseThetaStyle( implicit );    // Implicit joins use theta style (WHERE pk = fk), explicit joins use JOIN (afterQuery from)
+		joinSequence.addJoin( associationType, tableAlias, joinType, columns );
+		return joinSequence;
+	}
+
 	/**
 	 * Create a join sequence rooted at the given collection.
 	 *

hibernate-core/src/main/java/org/hibernate/loader/plan/exec/internal/LoadQueryJoinAndFetchProcessor.java

@@ -38,6 +38,7 @@ import org.hibernate.loader.plan.spi.QuerySpace;
 import org.hibernate.persister.collection.CollectionPersister;
 import org.hibernate.persister.collection.CollectionPropertyNames;
 import org.hibernate.persister.collection.QueryableCollection;
+import org.hibernate.persister.entity.AbstractEntityPersister;
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.persister.entity.Joinable;
 import org.hibernate.persister.entity.OuterJoinLoadable;
@@ -257,14 +258,35 @@ public class LoadQueryJoinAndFetchProcessor {
 				getJoinedAssociationTypeOrNull( join )
 		);
 
-		joinFragment.addJoin(
+		String[] joinColumns = join.resolveAliasedLeftHandSideJoinConditionColumns( lhsTableAlias );
-				joinable.getTableName(),
+		if ( joinColumns.length == 0 ) {
-				rhsTableAlias,
+			// When no columns are available, this is a special join that involves multiple subtypes
-				join.resolveAliasedLeftHandSideJoinConditionColumns( lhsTableAlias ),
+			AbstractEntityPersister persister = (AbstractEntityPersister) ( (EntityQuerySpace) join.getLeftHandSide() ).getEntityPersister();
-				join.resolveNonAliasedRightHandSideJoinConditionColumns(),
+
-				join.isRightHandSideRequired() ? JoinType.INNER_JOIN : JoinType.LEFT_OUTER_JOIN,
+			String[][] polyJoinColumns = persister.getPolymorphicJoinColumns(
-				additionalJoinConditions
+					lhsTableAlias,
-		);
+					( (JoinDefinedByMetadata) join ).getJoinedPropertyName()
+			);
+
+			joinFragment.addJoin(
+					joinable.getTableName(),
+					rhsTableAlias,
+					polyJoinColumns,
+					join.resolveNonAliasedRightHandSideJoinConditionColumns(),
+					join.isRightHandSideRequired() ? JoinType.INNER_JOIN : JoinType.LEFT_OUTER_JOIN,
+					additionalJoinConditions
+			);
+		}
+		else {
+			joinFragment.addJoin(
+					joinable.getTableName(),
+					rhsTableAlias,
+					joinColumns,
+					join.resolveNonAliasedRightHandSideJoinConditionColumns(),
+					join.isRightHandSideRequired() ? JoinType.INNER_JOIN : JoinType.LEFT_OUTER_JOIN,
+					additionalJoinConditions
+			);
+		}
 		joinFragment.addJoins(
 				joinable.fromJoinFragment( rhsTableAlias, false, true ),
 				joinable.whereJoinFragment( rhsTableAlias, false, true )

hibernate-core/src/main/java/org/hibernate/persister/entity/AbstractEntityPersister.java

@@ -5492,6 +5492,37 @@ public abstract class AbstractEntityPersister
 		return attributeDefinitions;
 	}
 
+	public String[][] getPolymorphicJoinColumns(String lhsTableAlias, String propertyPath) {
+		Set<String> subclassEntityNames = (Set<String>) getEntityMetamodel()
+				.getSubclassEntityNames();
+		// We will collect all the join columns from the LHS subtypes here
+		List<String[]> polymorphicJoinColumns = new ArrayList<>( subclassEntityNames.size() );
+
+		String[] joinColumns = null;
+
+		OUTER:
+		for ( String subclassEntityName : subclassEntityNames ) {
+			AbstractEntityPersister subclassPersister = (AbstractEntityPersister) getFactory()
+					.getMetamodel()
+					.entityPersister( subclassEntityName );
+			joinColumns = subclassPersister.toColumns( lhsTableAlias, propertyPath );
+
+			if ( joinColumns.length == 0 ) {
+				// The subtype does not have a "concrete" mapping for the property path
+				continue;
+			}
+
+			// Check for duplicates like this since we will mostly have just a few candidates
+			for ( String[] existingColumns : polymorphicJoinColumns ) {
+				if ( Arrays.deepEquals( existingColumns, joinColumns ) ) {
+					continue OUTER;
+				}
+			}
+			polymorphicJoinColumns.add( joinColumns );
+		}
+
+		return ArrayHelper.to2DStringArray( polymorphicJoinColumns );
+	}
 
 	private void prepareEntityIdentifierDefinition() {
 		if ( entityIdentifierDefinition != null ) {

hibernate-core/src/main/java/org/hibernate/persister/entity/AbstractPropertyMapping.java

@@ -11,15 +11,24 @@ import java.util.Map;
 
 import org.hibernate.MappingException;
 import org.hibernate.QueryException;
+import org.hibernate.boot.spi.MetadataImplementor;
 import org.hibernate.engine.spi.Mapping;
 import org.hibernate.internal.CoreLogging;
 import org.hibernate.internal.CoreMessageLogger;
 import org.hibernate.internal.util.StringHelper;
 import org.hibernate.internal.util.collections.ArrayHelper;
+import org.hibernate.mapping.Collection;
+import org.hibernate.mapping.MappedSuperclass;
+import org.hibernate.mapping.PersistentClass;
 import org.hibernate.sql.Template;
+import org.hibernate.type.AnyType;
 import org.hibernate.type.AssociationType;
+import org.hibernate.type.CollectionType;
 import org.hibernate.type.CompositeType;
 import org.hibernate.type.EntityType;
+import org.hibernate.type.ManyToOneType;
+import org.hibernate.type.OneToOneType;
+import org.hibernate.type.SpecialOneToOneType;
 import org.hibernate.type.Type;
 
 /**
@@ -109,6 +118,23 @@ public abstract class AbstractPropertyMapping implements PropertyMapping {
 		return result;
 	}
 
+	private void logDuplicateRegistration(String path, Type existingType, Type type) {
+		if ( LOG.isTraceEnabled() ) {
+			LOG.tracev(
+					"Skipping duplicate registration of path [{0}], existing type = [{1}], incoming type = [{2}]",
+					path,
+					existingType,
+					type
+			);
+		}
+	}
+
+	/**
+	 * Only kept around for compatibility reasons since this seems to be API.
+	 *
+	 * @deprecated Use {@link #addPropertyPath(String, Type, String[], String[], String[], String[], Mapping)} instead
+	 */
+	@Deprecated
 	protected void addPropertyPath(
 			String path,
 			Type type,
@@ -116,15 +142,96 @@ public abstract class AbstractPropertyMapping implements PropertyMapping {
 			String[] columnReaders,
 			String[] columnReaderTemplates,
 			String[] formulaTemplates) {
-		// TODO : not quite sure yet of the difference, but this is only needed from annotations for @Id @ManyToOne support
+		addPropertyPath( path, type, columns, columnReaders, columnReaderTemplates, formulaTemplates, null );
-		if ( typesByPropertyPath.containsKey( path ) ) {
+	}
-			if ( LOG.isTraceEnabled() ) {
+
-				LOG.tracev(
+	protected void addPropertyPath(
-						"Skipping duplicate registration of path [{0}], existing type = [{1}], incoming type = [{2}]",
+			String path,
+			Type type,
+			String[] columns,
+			String[] columnReaders,
+			String[] columnReaderTemplates,
+			String[] formulaTemplates,
+			Mapping factory) {
+		Type existingType = typesByPropertyPath.get( path );
+		if ( existingType != null ) {
+			// If types match or the new type is not an association type, there is nothing for us to do
+			if ( type == existingType || !( type instanceof AssociationType ) ) {
+				logDuplicateRegistration(
 						path,
-						typesByPropertyPath.get( path ),
+						existingType,
 						type
 				);
+				return;
+			}
+
+			// Workaround for org.hibernate.cfg.annotations.PropertyBinder.bind() adding a component for *ToOne ids
+			if ( !( existingType instanceof AssociationType ) ) {
+				logDuplicateRegistration(
+						path,
+						existingType,
+						type
+				);
+				return;
+			}
+
+			Type newType;
+			MetadataImplementor metadata = (MetadataImplementor) factory;
+
+			if ( type instanceof AnyType ) {
+				// TODO: not sure how to handle any types
+				throw new UnsupportedOperationException( "Not yet implemented!" );
+			}
+			else if ( type instanceof CollectionType ) {
+				Collection thisCollection = metadata.getCollectionBinding( ( (CollectionType) existingType ).getRole() );
+				Collection otherCollection = metadata.getCollectionBinding( ( (CollectionType) type ).getRole() );
+
+				if ( thisCollection == otherCollection ) {
+					logDuplicateRegistration(
+							path,
+							existingType,
+							type
+					);
+					return;
+				}
+
+				Collection commonCollection = getSuperCollection(
+						metadata,
+						thisCollection.getOwner(),
+						otherCollection.getOwner(),
+						thisCollection.getReferencedPropertyName()
+				);
+
+				newType = commonCollection.getType();
+			}
+			else if ( type instanceof EntityType ) {
+				EntityType entityType1 = (EntityType) existingType;
+				EntityType entityType2 = (EntityType) type;
+
+				if ( entityType1.getAssociatedEntityName().equals( entityType2.getAssociatedEntityName() ) ) {
+					logDuplicateRegistration(
+							path,
+							existingType,
+							type
+					);
+					return;
+				}
+
+				newType = getCommonType( metadata, entityType1, entityType2 );
+			}
+			else {
+				throw new IllegalStateException( "Unexpected association type: " + type );
+			}
+
+			typesByPropertyPath.put( path, newType );
+			// Set everything to empty to signal action has to be taken!
+			// org.hibernate.hql.internal.ast.tree.DotNode.dereferenceEntityJoin() is reacting to this
+			String[] empty = new String[0];
+			columnsByPropertyPath.put( path, empty );
+			columnReadersByPropertyPath.put( path, empty );
+			columnReaderTemplatesByPropertyPath.put( path, empty );
+			if ( formulaTemplates != null ) {
+				formulaTemplatesByPropertyPath.put( path, empty );
 			}
 			return;
 		}
@@ -137,6 +244,102 @@ public abstract class AbstractPropertyMapping implements PropertyMapping {
 		}
 	}
 
+	private Type getCommonType(MetadataImplementor metadata, EntityType entityType1, EntityType entityType2) {
+		PersistentClass thisClass = metadata.getEntityBinding( entityType1.getAssociatedEntityName() );
+		PersistentClass otherClass = metadata.getEntityBinding( entityType2.getAssociatedEntityName() );
+		PersistentClass commonClass = getCommonPersistentClass( thisClass, otherClass );
+
+		// Create a copy of the type but with the common class
+		if ( entityType1 instanceof ManyToOneType ) {
+			ManyToOneType t = (ManyToOneType) entityType1;
+			return new ManyToOneType( t, commonClass.getEntityName() );
+		}
+		else if ( entityType1 instanceof SpecialOneToOneType ) {
+			SpecialOneToOneType t = (SpecialOneToOneType) entityType1;
+			return new SpecialOneToOneType( t, commonClass.getEntityName() );
+		}
+		else if ( entityType1 instanceof OneToOneType ) {
+			OneToOneType t = (OneToOneType) entityType1;
+			return new OneToOneType( t, commonClass.getEntityName() );
+		}
+		else {
+			throw new IllegalStateException( "Unexpected entity type: " + entityType1 );
+		}
+	}
+
+	private PersistentClass getCommonPersistentClass(PersistentClass clazz1, PersistentClass clazz2) {
+		while ( !clazz2.getMappedClass().isAssignableFrom( clazz1.getMappedClass() ) ) {
+			clazz2 = clazz2.getSuperclass();
+		}
+		return clazz2;
+	}
+
+	private Collection getSuperCollection(MetadataImplementor metadata, PersistentClass clazz1, PersistentClass commonPersistentClass, String propertyName) {
+		Class<?> c1 = clazz1.getMappedClass();
+		Class<?> c2 = commonPersistentClass.getMappedClass();
+		MappedSuperclass commonMappedSuperclass = null;
+
+		// First we traverse up the clazz2/commonPersistentClass super types until we find a common type
+		while ( !c2.isAssignableFrom( c1 ) ) {
+			if ( commonPersistentClass == null) {
+				if ( commonMappedSuperclass.getSuperPersistentClass() == null ) {
+					commonMappedSuperclass = commonMappedSuperclass.getSuperMappedSuperclass();
+					commonPersistentClass = null;
+				}
+				else {
+					commonPersistentClass = commonMappedSuperclass.getSuperPersistentClass();
+					commonMappedSuperclass = null;
+				}
+			}
+			else {
+				if ( commonPersistentClass.getSuperclass() == null ) {
+					commonMappedSuperclass = commonPersistentClass.getSuperMappedSuperclass();
+					commonPersistentClass = null;
+				}
+				else {
+					commonPersistentClass = commonPersistentClass.getSuperclass();
+					commonMappedSuperclass = null;
+				}
+			}
+		}
+
+		// Then we traverse it's types up as long as possible until we find a type that has a collection binding
+		while ( c2 != Object.class ) {
+			if ( commonMappedSuperclass != null ) {
+				Collection collection = metadata.getCollectionBinding( commonMappedSuperclass.getMappedClass().getName() + "." + propertyName );
+				if ( collection != null ) {
+					return collection;
+				}
+
+				if ( commonMappedSuperclass.getSuperPersistentClass() == null ) {
+					commonMappedSuperclass = commonMappedSuperclass.getSuperMappedSuperclass();
+					commonPersistentClass = null;
+				}
+				else {
+					commonPersistentClass = commonMappedSuperclass.getSuperPersistentClass();
+					commonMappedSuperclass = null;
+				}
+			}
+			else {
+				Collection collection = metadata.getCollectionBinding( commonPersistentClass.getEntityName() + "." + propertyName );
+				if ( collection != null ) {
+					return collection;
+				}
+
+				if ( commonPersistentClass.getSuperclass() == null ) {
+					commonMappedSuperclass = commonPersistentClass.getSuperMappedSuperclass();
+					commonPersistentClass = null;
+				}
+				else {
+					commonPersistentClass = commonPersistentClass.getSuperclass();
+					commonMappedSuperclass = null;
+				}
+			}
+		}
+
+		return null;
+	}
+
 	/*protected void initPropertyPaths(
 			final String path,
 			final Type type,
@@ -189,7 +392,7 @@ public abstract class AbstractPropertyMapping implements PropertyMapping {
 		}
 
 		if ( path != null ) {
-			addPropertyPath( path, type, columns, columnReaders, columnReaderTemplates, formulaTemplates );
+			addPropertyPath( path, type, columns, columnReaders, columnReaderTemplates, formulaTemplates, factory );
 		}
 
 		if ( type.isComponentType() ) {
@@ -242,14 +445,14 @@ public abstract class AbstractPropertyMapping implements PropertyMapping {
 		if ( etype.isReferenceToPrimaryKey() ) {
 			if ( !hasNonIdentifierPropertyNamedId ) {
 				String idpath1 = extendPath( path, EntityPersister.ENTITY_ID );
-				addPropertyPath( idpath1, idtype, columns, columnReaders, columnReaderTemplates, null );
+				addPropertyPath( idpath1, idtype, columns, columnReaders, columnReaderTemplates, null, factory );
 				initPropertyPaths( idpath1, idtype, columns, columnReaders, columnReaderTemplates, null, factory );
 			}
 		}
 
 		if ( idPropName != null ) {
 			String idpath2 = extendPath( path, idPropName );
-			addPropertyPath( idpath2, idtype, columns, columnReaders, columnReaderTemplates, null );
+			addPropertyPath( idpath2, idtype, columns, columnReaders, columnReaderTemplates, null, factory );
 			initPropertyPaths( idpath2, idtype, columns, columnReaders, columnReaderTemplates, null, factory );
 		}
 	}

hibernate-core/src/main/java/org/hibernate/sql/ANSIJoinFragment.java

@@ -89,6 +89,63 @@ public class ANSIJoinFragment extends JoinFragment {
 
 	}
 
+	public void addJoin(
+			String rhsTableName,
+			String rhsAlias,
+			String[][] lhsColumns,
+			String[] rhsColumns,
+			JoinType joinType,
+			String on) {
+		final String joinString;
+		switch (joinType) {
+			case INNER_JOIN:
+				joinString = " inner join ";
+				break;
+			case LEFT_OUTER_JOIN:
+				joinString = " left outer join ";
+				break;
+			case RIGHT_OUTER_JOIN:
+				joinString = " right outer join ";
+				break;
+			case FULL_JOIN:
+				joinString = " full outer join ";
+				break;
+			default:
+				throw new AssertionFailure("undefined join type");
+		}
+
+		this.buffer.append(joinString)
+				.append(rhsTableName)
+				.append(' ')
+				.append(rhsAlias)
+				.append(" on ");
+
+
+		if ( lhsColumns.length > 1 ) {
+			this.buffer.append( "(" );
+		}
+		for ( int i = 0; i < lhsColumns.length; i++ ) {
+			for ( int j=0; j<lhsColumns[i].length; j++) {
+				this.buffer.append( lhsColumns[i][j] )
+						.append('=')
+						.append(rhsAlias)
+						.append('.')
+						.append( rhsColumns[j] );
+				if ( j < lhsColumns[i].length-1 ) {
+					this.buffer.append( " and " );
+				}
+			}
+			if ( i < lhsColumns.length - 1 ) {
+				this.buffer.append( " or " );
+			}
+		}
+		if ( lhsColumns.length > 1 ) {
+			this.buffer.append( ")" );
+		}
+
+		addCondition( buffer, on );
+	}
+
 	@Override
 	public String toFromFragmentString() {
 		return this.buffer.toString();

hibernate-core/src/main/java/org/hibernate/sql/JoinFragment.java

@@ -76,6 +76,23 @@ public abstract class JoinFragment {
 	 */
 	public abstract void addJoin(String tableName, String alias, String[] fkColumns, String[] pkColumns, JoinType joinType, String on);
 
+	/**
+	 * Adds a join, with an additional ON clause fragment
+	 *
+	 * @param tableName The name of the table to be joined
+	 * @param alias The alias to apply to the joined table
+	 * @param fkColumns The names of the columns which reference the joined table
+	 * @param pkColumns The columns in the joined table being referenced
+	 * @param joinType The type of join
+	 * @param on The additional ON fragment
+	 */
+	public void addJoin(String tableName, String alias, String[][] fkColumns, String[] pkColumns, JoinType joinType, String on) {
+		if ( fkColumns.length > 1 ) {
+			throw new UnsupportedOperationException( "The join fragment does not support multiple foreign key columns: " + getClass() );
+		}
+		addJoin( tableName, alias, fkColumns[0], pkColumns, joinType, on );
+	}
+
 	/**
 	 * Adds a cross join to the specified table.
 	 *

hibernate-core/src/main/java/org/hibernate/sql/OracleJoinFragment.java

@@ -38,6 +38,40 @@ public class OracleJoinFragment extends JoinFragment {
 		}
 	}
 
+	public void addJoin(String tableName, String alias, String[][] fkColumns, String[] pkColumns, JoinType joinType) {
+		addCrossJoin( tableName, alias );
+
+		if ( fkColumns.length > 1 ) {
+			afterWhere.append( "(" );
+		}
+		for ( int i = 0; i < fkColumns.length; i++ ) {
+			afterWhere.append( " and " );
+			for ( int j = 0; j < fkColumns[i].length; j++ ) {
+				setHasThetaJoins( true );
+				afterWhere.append( fkColumns[i][j] );
+				if ( joinType == JoinType.RIGHT_OUTER_JOIN || joinType == JoinType.FULL_JOIN ) {
+					afterWhere.append( "(+)" );
+				}
+				afterWhere.append( '=' )
+						.append( alias )
+						.append( '.' )
+						.append( pkColumns[j] );
+				if ( joinType == JoinType.LEFT_OUTER_JOIN || joinType == JoinType.FULL_JOIN ) {
+					afterWhere.append( "(+)" );
+				}
+				if ( j < fkColumns[i].length - 1 ) {
+					afterWhere.append( " and " );
+				}
+			}
+			if ( i < fkColumns.length - 1 ) {
+				afterWhere.append( " or " );
+			}
+		}
+		if ( fkColumns.length > 1 ) {
+			afterWhere.append( ")" );
+		}
+	}
+
 	public String toFromFragmentString() {
 		return afterFrom.toString();
 	}
@@ -101,6 +135,20 @@ public class OracleJoinFragment extends JoinFragment {
 		}
 	}
 
+	public void addJoin(String tableName, String alias, String[][] fkColumns, String[] pkColumns, JoinType joinType, String on) {
+		//arbitrary on clause ignored!!
+		addJoin( tableName, alias, fkColumns, pkColumns, joinType );
+		if ( joinType == JoinType.INNER_JOIN ) {
+			addCondition( on );
+		}
+		else if ( joinType == JoinType.LEFT_OUTER_JOIN ) {
+			addLeftOuterJoinCondition( on );
+		}
+		else {
+			throw new UnsupportedOperationException( "join type not supported by OracleJoinFragment (use Oracle9iDialect/Oracle10gDialect)" );
+		}
+	}
+
 	/**
 	 * This method is a bit of a hack, and assumes
 	 * that the column on the "right" side of the

hibernate-core/src/main/java/org/hibernate/sql/QueryJoinFragment.java

@@ -6,6 +6,7 @@
  */
 package org.hibernate.sql;
 import org.hibernate.dialect.Dialect;
+import org.hibernate.internal.util.StringHelper;
 
 /**
  * A join that appears in a translated HQL query
@@ -32,6 +33,14 @@ public class QueryJoinFragment extends JoinFragment {
 		addJoin( tableName, alias, alias, fkColumns, pkColumns, joinType, on );
 	}
 
+	public void addJoin(String tableName, String alias, String[][] fkColumns, String[] pkColumns, JoinType joinType) {
+		addJoin( tableName, alias, alias, fkColumns, pkColumns, joinType, null );
+	}
+
+	public void addJoin(String tableName, String alias, String[][] fkColumns, String[] pkColumns, JoinType joinType, String on) {
+		addJoin( tableName, alias, alias, fkColumns, pkColumns, joinType, on );
+	}
+
 	private void addJoin(String tableName, String alias, String concreteAlias, String[] fkColumns, String[] pkColumns, JoinType joinType, String on) {
 		if ( !useThetaStyleInnerJoins || joinType != JoinType.INNER_JOIN ) {
 			JoinFragment jf = dialect.createOuterJoinFragment();
@@ -45,6 +54,19 @@ public class QueryJoinFragment extends JoinFragment {
 		}
 	}
 
+	private void addJoin(String tableName, String alias, String concreteAlias, String[][] fkColumns, String[] pkColumns, JoinType joinType, String on) {
+		if ( !useThetaStyleInnerJoins || joinType != JoinType.INNER_JOIN ) {
+			JoinFragment jf = dialect.createOuterJoinFragment();
+			jf.addJoin( tableName, alias, fkColumns, pkColumns, joinType, on );
+			addFragment( jf );
+		}
+		else {
+			addCrossJoin( tableName, alias );
+			addCondition( concreteAlias, fkColumns, pkColumns );
+			addCondition( on );
+		}
+	}
+
 	public String toFromFragmentString() {
 		return afterFrom.toString();
 	}
@@ -94,6 +116,31 @@ public class QueryJoinFragment extends JoinFragment {
 		}
 	}
 
+	public void addCondition(String alias, String[][] fkColumns, String[] pkColumns) {
+		afterWhere.append( " and " );
+		if ( fkColumns.length > 1 ) {
+			afterWhere.append( "(" );
+		}
+		for ( int i = 0; i < fkColumns.length; i++ ) {
+			for ( int j = 0; j < fkColumns[i].length; j++ ) {
+				afterWhere.append( fkColumns[i][j] )
+						.append( '=' )
+						.append( alias )
+						.append( '.' )
+						.append( pkColumns[j] );
+				if ( j < fkColumns[i].length - 1 ) {
+					afterWhere.append( " and " );
+				}
+			}
+			if ( i < fkColumns.length - 1 ) {
+				afterWhere.append( " or " );
+			}
+		}
+		if ( fkColumns.length > 1 ) {
+			afterWhere.append( ")" );
+		}
+	}
+
 	/**
 	 * Add the condition string to the join fragment.
 	 *
@@ -103,6 +150,7 @@ public class QueryJoinFragment extends JoinFragment {
 	public boolean addCondition(String condition) {
 		// if the condition is not already there...
 		if (
+				!StringHelper.isEmpty( condition ) &&
 				afterFrom.toString().indexOf( condition.trim() ) < 0 &&
 				afterWhere.toString().indexOf( condition.trim() ) < 0
 		) {

hibernate-core/src/main/java/org/hibernate/sql/Sybase11JoinFragment.java

@@ -47,6 +47,49 @@ public class Sybase11JoinFragment extends JoinFragment {
 		}
 	}
 
+	public void addJoin(String tableName, String alias, String[][] fkColumns, String[] pkColumns, JoinType joinType) {
+
+		addCrossJoin( tableName, alias );
+
+		if ( fkColumns.length > 1 ) {
+			afterWhere.append( "(" );
+		}
+		for ( int i = 0; i < fkColumns.length; i++ ) {
+			afterWhere.append( " and " );
+			for ( int j = 0; j < fkColumns[i].length; j++ ) {
+				//full joins are not supported.. yet!
+				if ( joinType == JoinType.FULL_JOIN ) {
+					throw new UnsupportedOperationException();
+				}
+
+				afterWhere.append( fkColumns[i][j] )
+						.append( " " );
+
+				if ( joinType == JoinType.LEFT_OUTER_JOIN ) {
+					afterWhere.append( '*' );
+				}
+				afterWhere.append( '=' );
+				if ( joinType == JoinType.RIGHT_OUTER_JOIN ) {
+					afterWhere.append( "*" );
+				}
+
+				afterWhere.append( " " )
+						.append( alias )
+						.append( '.' )
+						.append( pkColumns[j] );
+				if ( j < fkColumns[i].length - 1 ) {
+					afterWhere.append( " and " );
+				}
+			}
+			if ( i < fkColumns.length - 1 ) {
+				afterWhere.append( " or " );
+			}
+		}
+		if ( fkColumns.length > 1 ) {
+			afterWhere.append( ")" );
+		}
+	}
+
 	public String toFromFragmentString() {
 		return afterFrom.toString();
 	}
@@ -109,4 +152,15 @@ public class Sybase11JoinFragment extends JoinFragment {
 		addJoin( tableName, alias, fkColumns, pkColumns, joinType );
 		addCondition( on );
 	}
+
+	public void addJoin(
+			String tableName,
+			String alias,
+			String[][] fkColumns,
+			String[] pkColumns,
+			JoinType joinType,
+			String on) {
+		addJoin( tableName, alias, fkColumns, pkColumns, joinType );
+		addCondition( on );
+	}
 }

hibernate-core/src/main/java/org/hibernate/type/EntityType.java

@@ -111,6 +111,15 @@ public abstract class EntityType extends AbstractType implements AssociationType
 		this.referenceToPrimaryKey = referenceToPrimaryKey;
 	}
 
+	protected EntityType(EntityType original, String superTypeEntityName) {
+		this.scope = original.scope;
+		this.associatedEntityName = superTypeEntityName;
+		this.uniqueKeyPropertyName = original.uniqueKeyPropertyName;
+		this.eager = original.eager;
+		this.unwrapProxy = original.unwrapProxy;
+		this.referenceToPrimaryKey = original.referenceToPrimaryKey;
+	}
+
 	protected TypeFactory.TypeScope scope() {
 		return scope;
 	}

hibernate-core/src/main/java/org/hibernate/type/ManyToOneType.java

@@ -83,6 +83,12 @@ public class ManyToOneType extends EntityType {
 		this.isLogicalOneToOne = isLogicalOneToOne;
 	}
 
+	public ManyToOneType(ManyToOneType original, String superTypeEntityName) {
+		super( original, superTypeEntityName );
+		this.ignoreNotFound = original.ignoreNotFound;
+		this.isLogicalOneToOne = original.isLogicalOneToOne;
+	}
+
 	@Override
 	protected boolean isNullable() {
 		return ignoreNotFound;

hibernate-core/src/main/java/org/hibernate/type/OneToOneType.java

@@ -63,6 +63,13 @@ public class OneToOneType extends EntityType {
 		this.entityName = entityName;
 	}
 
+	public OneToOneType(OneToOneType original, String superTypeEntityName) {
+		super( original, superTypeEntityName );
+		this.foreignKeyType = original.foreignKeyType;
+		this.propertyName = original.propertyName;
+		this.entityName = original.entityName;
+	}
+
 	@Override
 	public String getPropertyName() {
 		return propertyName;

hibernate-core/src/main/java/org/hibernate/type/SpecialOneToOneType.java

@@ -64,6 +64,10 @@ public class SpecialOneToOneType extends OneToOneType {
 				propertyName
 			);
 	}
+
+	public SpecialOneToOneType(SpecialOneToOneType original, String superTypeEntityName) {
+		super( original, superTypeEntityName );
+	}
 	
 	public int getColumnSpan(Mapping mapping) throws MappingException {
 		return super.getIdentifierOrUniqueKeyType( mapping ).getColumnSpan( mapping );

hibernate-core/src/test/java/org/hibernate/test/inheritance/discriminator/MultiInheritanceImplicitDowncastTest.java

@@ -0,0 +1,614 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * Copyright (c) 2014, Red Hat Inc. or third-party contributors as
+ * indicated by the @author tags or express copyright attribution
+ * statements applied by the authors.  All third-party contributions are
+ * distributed under license by Red Hat Inc.
+ *
+ * This copyrighted material is made available to anyone wishing to use, modify,
+ * copy, or redistribute it subject to the terms and conditions of the GNU
+ * Lesser General Public License, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this distribution; if not, write to:
+ * Free Software Foundation, Inc.
+ * 51 Franklin Street, Fifth Floor
+ * Boston, MA  02110-1301  USA
+ */
+package org.hibernate.test.inheritance.discriminator;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import javax.persistence.AssociationOverride;
+import javax.persistence.AssociationOverrides;
+import javax.persistence.Basic;
+import javax.persistence.DiscriminatorColumn;
+import javax.persistence.Embeddable;
+import javax.persistence.Embedded;
+import javax.persistence.Entity;
+import javax.persistence.FetchType;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.Inheritance;
+import javax.persistence.InheritanceType;
+import javax.persistence.JoinColumn;
+import javax.persistence.JoinTable;
+import javax.persistence.ManyToOne;
+import javax.persistence.MapKeyColumn;
+import javax.persistence.MappedSuperclass;
+import javax.persistence.OneToMany;
+import javax.persistence.OrderColumn;
+
+import org.hibernate.Session;
+import org.hibernate.engine.query.spi.HQLQueryPlan;
+import org.hibernate.hql.spi.QueryTranslator;
+
+import org.hibernate.testing.junit4.BaseCoreFunctionalTestCase;
+import org.junit.Test;
+
+import static org.hibernate.testing.transaction.TransactionUtil.doInHibernate;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+/**
+ * @author Christian Beikov
+ */
+public class MultiInheritanceImplicitDowncastTest extends BaseCoreFunctionalTestCase {
+
+	@Override
+	protected Class<?>[] getAnnotatedClasses() {
+		return new Class[] {
+				IntIdEntity.class,
+				NameObject.class,
+				PolymorphicBase.class,
+				PolymorphicPropertyBase.class,
+				PolymorphicPropertyMapBase.class,
+				PolymorphicPropertySub1.class,
+				PolymorphicPropertySub2.class,
+				PolymorphicSub1.class,
+				PolymorphicSub2.class
+		};
+	}
+
+	@Test
+	public void testQueryingSingle() {
+		doInHibernate( this::sessionFactory, s -> {
+			final String base = "from PolymorphicPropertyBase p left join ";
+			s.createQuery( base + "p.base b left join b.relation1 " ).getResultList();
+			s.createQuery( base + "p.base b left join b.relation2 " ).getResultList();
+			s.createQuery( base + "p.baseEmbeddable.embeddedRelation1 b left join b.relation1" ).getResultList();
+			s.createQuery( base + "p.baseEmbeddable.embeddedRelation2 b left join b.relation2" ).getResultList();
+			s.createQuery( base + "p.baseEmbeddable.embeddedBase b left join b.relation1" ).getResultList();
+			s.createQuery( base + "p.baseEmbeddable.embeddedBase b left join b.relation2" ).getResultList();
+		} );
+	}
+
+	@Test
+	public void testQueryingMultiple() {
+		doInHibernate( this::sessionFactory, s -> {
+			final String base = "from PolymorphicPropertyBase p left join ";
+			s.createQuery( base + "p.base b left join b.relation1 left join b.relation2" ).getResultList();
+			s.createQuery( base + "p.base b left join b.relation2 left join b.relation1" ).getResultList();
+			s.createQuery( base + "p.baseEmbeddable.embeddedBase b left join b.relation1 left join b.relation2" ).getResultList();
+			s.createQuery( base + "p.baseEmbeddable.embeddedBase b left join b.relation2 left join b.relation1" ).getResultList();
+		} );
+	}
+
+	@Test
+	public void testMultiJoinAddition1() {
+		testMultiJoinAddition( "from PolymorphicPropertyBase p left join p.base b left join b.relation1" );
+	}
+
+	@Test
+	public void testMultiJoinAddition2() {
+		testMultiJoinAddition( "from PolymorphicPropertyBase p left join p.base b left join b.relation2" );
+	}
+
+	private void testMultiJoinAddition(String hql) {
+		final HQLQueryPlan plan = sessionFactory().getQueryPlanCache().getHQLQueryPlan(
+				hql,
+				false,
+				Collections.EMPTY_MAP
+		);
+		assertEquals( 1, plan.getTranslators().length );
+		final QueryTranslator translator = plan.getTranslators()[0];
+		final String generatedSql = translator.getSQLString();
+
+		int sub1JoinColumnIndex = generatedSql.indexOf( ".base_sub_1" );
+		assertNotEquals(
+				"Generated SQL doesn't contain a join for 'base' with 'PolymorphicSub1' via 'base_sub_1':\n" + generatedSql,
+				-1,
+				sub1JoinColumnIndex
+		);
+		int sub2JoinColumnIndex = generatedSql.indexOf( ".base_sub_2" );
+		assertNotEquals(
+				"Generated SQL doesn't contain a join for 'base' with 'PolymorphicSub2' via 'base_sub_2':\n" + generatedSql,
+				-1,
+				sub2JoinColumnIndex
+		);
+	}
+
+	@MappedSuperclass
+	public abstract static class BaseEmbeddable<T extends PolymorphicBase> implements Serializable {
+		private static final long serialVersionUID = 1L;
+
+		private String someName;
+		private T embeddedBase;
+
+		public BaseEmbeddable() {
+		}
+
+		public String getSomeName() {
+			return someName;
+		}
+
+		public void setSomeName(String someName) {
+			this.someName = someName;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public T getEmbeddedBase() {
+			return embeddedBase;
+		}
+
+		public void setEmbeddedBase(T embeddedBase) {
+			this.embeddedBase = embeddedBase;
+		}
+	}
+
+	@Embeddable
+	public abstract static class Embeddable1 extends BaseEmbeddable<PolymorphicSub1> {
+		private static final long serialVersionUID = 1L;
+
+		private String someName1;
+		private PolymorphicSub1 embeddedRelation1;
+
+		public Embeddable1() {
+		}
+
+		public String getSomeName1() {
+			return someName1;
+		}
+
+		public void setSomeName1(String someName1) {
+			this.someName1 = someName1;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public PolymorphicSub1 getEmbeddedRelation1() {
+			return embeddedRelation1;
+		}
+
+		public void setEmbeddedRelation1(PolymorphicSub1 embeddedRelation1) {
+			this.embeddedRelation1 = embeddedRelation1;
+		}
+	}
+
+	@Embeddable
+	public abstract static class Embeddable2 extends BaseEmbeddable<PolymorphicSub2> {
+		private static final long serialVersionUID = 1L;
+
+		private String someName2;
+		private PolymorphicSub2 embeddedRelation2;
+
+		public Embeddable2() {
+		}
+
+		public String getSomeName2() {
+			return someName2;
+		}
+
+		public void setSomeName2(String someName2) {
+			this.someName2 = someName2;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public PolymorphicSub2 getEmbeddedRelation2() {
+			return embeddedRelation2;
+		}
+
+		public void setEmbeddedRelation2(PolymorphicSub2 embeddedRelation2) {
+			this.embeddedRelation2 = embeddedRelation2;
+		}
+	}
+
+	@Entity(name = "IntIdEntity")
+	public static class IntIdEntity implements Serializable {
+		private static final long serialVersionUID = 1L;
+
+		private Integer id;
+		private String name;
+
+		public IntIdEntity() {
+		}
+
+		public IntIdEntity(String name) {
+			this.name = name;
+		}
+
+		@Id
+		@GeneratedValue
+		public Integer getId() {
+			return id;
+		}
+
+		public void setId(Integer id) {
+			this.id = id;
+		}
+
+		@Basic(optional = false)
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		@Override
+		public int hashCode() {
+			final int prime = 31;
+			int result = 1;
+			result = prime * result + ( ( id == null ) ? 0 : id.hashCode() );
+			return result;
+		}
+
+		@Override
+		public boolean equals(Object obj) {
+			if ( this == obj ) {
+				return true;
+			}
+			if ( obj == null ) {
+				return false;
+			}
+			if ( getClass() != obj.getClass() ) {
+				return false;
+			}
+			IntIdEntity other = (IntIdEntity) obj;
+			if ( id == null ) {
+				if ( other.id != null ) {
+					return false;
+				}
+			}
+			else if ( !id.equals( other.id ) ) {
+				return false;
+			}
+			return true;
+		}
+	}
+
+	@Embeddable
+	public static class NameObject implements Serializable {
+
+		private String primaryName;
+		private String secondaryName;
+		private IntIdEntity intIdEntity;
+
+		public NameObject() {
+		}
+
+		public NameObject(String primaryName, String secondaryName) {
+			this.primaryName = primaryName;
+			this.secondaryName = secondaryName;
+		}
+
+		public String getPrimaryName() {
+			return primaryName;
+		}
+
+		public void setPrimaryName(String primaryName) {
+			this.primaryName = primaryName;
+		}
+
+		public String getSecondaryName() {
+			return secondaryName;
+		}
+
+		public void setSecondaryName(String secondaryName) {
+			this.secondaryName = secondaryName;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		@JoinColumn(name = "name_object_int_id_entity")
+		public IntIdEntity getIntIdEntity() {
+			return intIdEntity;
+		}
+
+		public void setIntIdEntity(IntIdEntity intIdEntity) {
+			this.intIdEntity = intIdEntity;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if ( this == o ) {
+				return true;
+			}
+			if ( !( o instanceof NameObject ) ) {
+				return false;
+			}
+
+			NameObject that = (NameObject) o;
+
+			if ( primaryName != null ? !primaryName.equals( that.primaryName ) : that.primaryName != null ) {
+				return false;
+			}
+			return secondaryName != null ? secondaryName.equals( that.secondaryName ) : that.secondaryName == null;
+
+		}
+
+		@Override
+		public int hashCode() {
+			int result = primaryName != null ? primaryName.hashCode() : 0;
+			result = 31 * result + ( secondaryName != null ? secondaryName.hashCode() : 0 );
+			return result;
+		}
+	}
+
+	@Entity(name = "PolymorphicBase")
+	@Inheritance(strategy = InheritanceType.JOINED)
+	public abstract static class PolymorphicBase implements Serializable {
+		private static final long serialVersionUID = 1L;
+
+		private Long id;
+		private String name;
+		private PolymorphicBase parent;
+		private List<PolymorphicBase> list = new ArrayList<PolymorphicBase>();
+		private Set<PolymorphicBase> children = new HashSet<PolymorphicBase>();
+		private Map<String, PolymorphicBase> map = new HashMap<String, PolymorphicBase>();
+
+		public PolymorphicBase() {
+		}
+
+		@Id
+		@GeneratedValue
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY, optional = true)
+		public PolymorphicBase getParent() {
+			return parent;
+		}
+
+		public void setParent(PolymorphicBase parent) {
+			this.parent = parent;
+		}
+
+		@OneToMany
+		@OrderColumn(name = "list_idx", nullable = false)
+		@JoinTable(name = "polymorphic_list")
+		public List<PolymorphicBase> getList() {
+			return list;
+		}
+
+		public void setList(List<PolymorphicBase> list) {
+			this.list = list;
+		}
+
+		@OneToMany(mappedBy = "parent")
+		public Set<PolymorphicBase> getChildren() {
+			return children;
+		}
+
+		public void setChildren(Set<PolymorphicBase> children) {
+			this.children = children;
+		}
+
+		@OneToMany
+		@JoinTable(name = "polymorphic_map")
+		@MapKeyColumn(length = 20, nullable = false)
+		public Map<String, PolymorphicBase> getMap() {
+			return map;
+		}
+
+		public void setMap(Map<String, PolymorphicBase> map) {
+			this.map = map;
+		}
+	}
+
+	@Entity(name = "PolymorphicPropertyBase")
+	@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
+	@DiscriminatorColumn(name = "PROP_TYPE")
+	public abstract static class PolymorphicPropertyBase implements Serializable {
+
+		private static final long serialVersionUID = 1L;
+
+		private Long id;
+		private String name;
+
+		public PolymorphicPropertyBase() {
+		}
+
+		@Id
+		@GeneratedValue
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+
+	@MappedSuperclass
+	public abstract static class PolymorphicPropertyMapBase<T extends PolymorphicBase, E extends BaseEmbeddable> extends
+			PolymorphicPropertyBase {
+
+		private static final long serialVersionUID = 1L;
+
+		private T base;
+		private E baseEmbeddable;
+
+		public PolymorphicPropertyMapBase() {
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public T getBase() {
+			return base;
+		}
+
+		public void setBase(T base) {
+			this.base = base;
+		}
+
+		@Embedded
+		public E getBaseEmbeddable() {
+			return baseEmbeddable;
+		}
+
+		public void setBaseEmbeddable(E baseEmbeddable) {
+			this.baseEmbeddable = baseEmbeddable;
+		}
+	}
+
+	@Entity(name = "PolymorphicPropertySub1")
+	@AssociationOverrides({
+			@AssociationOverride(name = "base", joinColumns = @JoinColumn(name = "base_sub_1"))
+	})
+	public static class PolymorphicPropertySub1 extends PolymorphicPropertyMapBase<PolymorphicSub1, Embeddable1> {
+		private static final long serialVersionUID = 1L;
+
+		public PolymorphicPropertySub1() {
+		}
+	}
+
+	@Entity(name = "PolymorphicPropertySub2")
+	@AssociationOverrides({
+			@AssociationOverride(name = "base", joinColumns = @JoinColumn(name = "base_sub_2"))
+	})
+	public static class PolymorphicPropertySub2 extends PolymorphicPropertyMapBase<PolymorphicSub2, Embeddable2> {
+		private static final long serialVersionUID = 1L;
+
+		public PolymorphicPropertySub2() {
+		}
+	}
+
+	@Entity(name = "PolymorphicSub1")
+	public static class PolymorphicSub1 extends PolymorphicBase {
+		private static final long serialVersionUID = 1L;
+
+		private IntIdEntity relation1;
+		private PolymorphicBase parent1;
+		private NameObject embeddable1;
+		private Integer sub1Value;
+
+		public PolymorphicSub1() {
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public IntIdEntity getRelation1() {
+			return relation1;
+		}
+
+		public void setRelation1(IntIdEntity relation1) {
+			this.relation1 = relation1;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public PolymorphicBase getParent1() {
+			return parent1;
+		}
+
+		public void setParent1(PolymorphicBase parent1) {
+			this.parent1 = parent1;
+		}
+
+		@Embedded
+		public NameObject getEmbeddable1() {
+			return embeddable1;
+		}
+
+		public void setEmbeddable1(NameObject embeddable1) {
+			this.embeddable1 = embeddable1;
+		}
+
+		public Integer getSub1Value() {
+			return sub1Value;
+		}
+
+		public void setSub1Value(Integer sub1Value) {
+			this.sub1Value = sub1Value;
+		}
+	}
+
+	@Entity(name = "PolymorphicSub2")
+	public static class PolymorphicSub2 extends PolymorphicBase {
+		private static final long serialVersionUID = 1L;
+
+		private IntIdEntity relation2;
+		private PolymorphicBase parent2;
+		private NameObject embeddable2;
+		private Integer sub2Value;
+
+		public PolymorphicSub2() {
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public IntIdEntity getRelation2() {
+			return relation2;
+		}
+
+		public void setRelation2(IntIdEntity relation2) {
+			this.relation2 = relation2;
+		}
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		public PolymorphicBase getParent2() {
+			return parent2;
+		}
+
+		public void setParent2(PolymorphicBase parent1) {
+			this.parent2 = parent1;
+		}
+
+		@Embedded
+		public NameObject getEmbeddable2() {
+			return embeddable2;
+		}
+
+		public void setEmbeddable2(NameObject embeddable1) {
+			this.embeddable2 = embeddable1;
+		}
+
+		public Integer getSub2Value() {
+			return sub2Value;
+		}
+
+		public void setSub2Value(Integer sub2Value) {
+			this.sub2Value = sub2Value;
+		}
+	}
+}

hibernate-core/src/test/java/org/hibernate/test/inheritance/discriminator/MultiSingleTableLoadTest.java

@@ -10,6 +10,7 @@ import java.io.Serializable;
 import javax.persistence.CascadeType;
 import javax.persistence.DiscriminatorValue;
 import javax.persistence.Entity;
+import javax.persistence.FetchType;
 import javax.persistence.Id;
 import javax.persistence.Inheritance;
 import javax.persistence.InheritanceType;
@@ -23,6 +24,7 @@ import org.junit.Test;
 
 import static org.hibernate.testing.transaction.TransactionUtil.doInHibernate;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
 
 /**
  * @author Christian Beikov
@@ -50,7 +52,7 @@ public class MultiSingleTableLoadTest extends BaseCoreFunctionalTestCase {
 
 	@Test
 	@TestForIssue(jiraKey = "HHH-5954")
-	public void testLoadMultipleHoldersWithDifferentSubtypes() {
+	public void testEagerLoadMultipleHoldersWithDifferentSubtypes() {
 		createTestData();
 		doInHibernate( this::sessionFactory, session -> {
 			Holder task1 = session.find( Holder.class, 1L );
@@ -60,12 +62,27 @@ public class MultiSingleTableLoadTest extends BaseCoreFunctionalTestCase {
 		} );
 	}
 
+	@Test
+	public void testFetchJoinLoadMultipleHoldersWithDifferentSubtypes() {
+		createTestData();
+		doInHibernate( this::sessionFactory, session -> {
+			Holder task1 = session.createQuery( "FROM Holder h JOIN FETCH h.a WHERE h.id = :id", Holder.class )
+					.setParameter( "id", 1L ).getSingleResult();
+			Holder task2 = session.createQuery( "FROM Holder h JOIN FETCH h.a WHERE h.id = :id", Holder.class )
+					.setParameter( "id", 2L ).getSingleResult();
+			assertNotNull( task1 );
+			assertNotNull( task2 );
+			assertTrue( task1.a instanceof B );
+			assertTrue( task2.a instanceof C );
+		} );
+	}
+
 	@Override
 	protected boolean isCleanupTestDataRequired() {
 		return true;
 	}
 
-	@Entity
+	@Entity(name = "Holder")
 	@Table(name = "holder")
 	public static class Holder implements Serializable {
 		@Id