Automatically generate check constraints for boolean and enum attributes

And make enums map to TINYINT by default.

hibernate-core/src/main/java/org/hibernate/mapping/BasicValue.java

@@ -11,7 +11,6 @@
 import java.util.function.Function;
 import java.util.function.Supplier;
 import javax.persistence.EnumType;
-import javax.persistence.TemporalType;
 
 import org.hibernate.HibernateException;
 import org.hibernate.MappingException;
@@ -26,6 +25,8 @@
 import org.hibernate.boot.registry.classloading.spi.ClassLoaderService;
 import org.hibernate.boot.registry.classloading.spi.ClassLoadingException;
 import org.hibernate.boot.spi.MetadataBuildingContext;
+import org.hibernate.dialect.Dialect;
+import org.hibernate.engine.jdbc.spi.JdbcServices;
 import org.hibernate.internal.util.ReflectHelper;
 import org.hibernate.internal.util.collections.CollectionHelper;
 import org.hibernate.metamodel.model.convert.internal.NamedEnumValueConverter;
@@ -72,7 +73,6 @@ public class BasicValue extends SimpleValue implements SqlTypeDescriptorIndicato
 	private boolean isNationalized;
 	private boolean isLob;
 	private EnumType enumerationStyle;
-	private TemporalType temporalPrecision;
 
 	private ConverterDescriptor attributeConverterDescriptor;
 
@@ -191,9 +191,7 @@ public Resolution<?> resolve() {
 					() -> {
 						if ( resolvedJavaClass != null ) {
 							//noinspection unchecked
-							return getBuildingContext().getBootstrapContext()
-									.getTypeConfiguration()
-									.getJavaTypeDescriptorRegistry()
+							return typeConfiguration.getJavaTypeDescriptorRegistry()
 									.resolveDescriptor( resolvedJavaClass );
 						}
 						else if ( ownerName != null && propertyName != null ) {
@@ -205,8 +203,7 @@ else if ( ownerName != null && propertyName != null ) {
 
 							// First resolve from the BasicTypeRegistry.
 							// If it does resolve, we can use the JTD instead of delegating to the JTD Regsitry.
-							final BasicType basicType = getBuildingContext().getBootstrapContext()
-									.getTypeConfiguration()
+							final BasicType basicType = typeConfiguration
 									.getBasicTypeRegistry()
 									.getRegisteredType( reflectedJavaType.getName() );
 							if ( basicType != null ) {
@@ -214,8 +211,7 @@ else if ( ownerName != null && propertyName != null ) {
 							}
 
 							//noinspection unchecked
-							return getBuildingContext().getBootstrapContext()
-									.getTypeConfiguration()
+							return typeConfiguration
 									.getJavaTypeDescriptorRegistry()
 									.resolveDescriptor( reflectedJavaType );
 						}
@@ -234,6 +230,30 @@ else if ( dependentValue != null ) {
 			);
 		}
 
+		if ( resolution != null
+				//TODO: pass in resolution.getValueConverter()
+				//and use it to determine the range of values!
+				&& attributeConverterDescriptor == null
+				&& getColumnSpan() == 1) {
+			Selectable selectable = getColumnIterator().next();
+			if (selectable instanceof Column) {
+				BasicType<?> basicType = resolution.getResolvedBasicType();
+				Column col = (Column) selectable;
+				Dialect dialect = getServiceRegistry().getService(JdbcServices.class).getDialect();
+				String checkConstraint = col.getCheckConstraint();
+				if ( checkConstraint == null && dialect.supportsColumnCheck() ) {
+					col.setCheckConstraint(
+							basicType.getJavaTypeDescriptor()
+									.getCheckCondition(
+											col.getQuotedName( dialect ),
+											basicType.getSqlTypeDescriptor(),
+											dialect
+									)
+					);
+				}
+			}
+		}
+
 		return resolution;
 	}
 

hibernate-core/src/main/java/org/hibernate/mapping/Column.java

@@ -292,6 +292,13 @@ public boolean hasCheckConstraint() {
 		return checkConstraint != null;
 	}
 
+	public String checkConstraint() {
+		if (checkConstraint==null) {
+			return null;
+		}
+		return " check (" + checkConstraint + ")";
+	}
+
 	@Override
 	public String getTemplate(Dialect dialect, SqmFunctionRegistry functionRegistry) {
 		return safeInterning(

hibernate-core/src/main/java/org/hibernate/mapping/Table.java

@@ -494,10 +494,9 @@ public Iterator sqlAlterStrings(
 							.getColumnDefinitionUniquenessFragment( column ) );
 				}
 
-				if ( column.hasCheckConstraint() && dialect.supportsColumnCheck() ) {
-					alter.append( " check(" )
-							.append( column.getCheckConstraint() )
-							.append( ")" );
+				String checkConstraint = column.checkConstraint();
+				if ( checkConstraint !=null && dialect.supportsColumnCheck() ) {
+					alter.append( checkConstraint );
 				}
 
 				String columnComment = column.getComment();
@@ -578,10 +577,9 @@ public String sqlCreateString(Dialect dialect, Mapping p, String defaultCatalog,
 						.getColumnDefinitionUniquenessFragment( col ) );
 			}
 
-			if ( col.hasCheckConstraint() && dialect.supportsColumnCheck() ) {
-				buf.append( " check (" )
-						.append( col.getCheckConstraint() )
-						.append( ")" );
+			String checkConstraint = col.checkConstraint();
+			if ( checkConstraint!=null && dialect.supportsColumnCheck() ) {
+				buf.append( checkConstraint );
 			}
 
 			String columnComment = col.getComment();

hibernate-core/src/main/java/org/hibernate/mapping/ToOne.java

@@ -26,7 +26,6 @@ public abstract class ToOne extends SimpleValue implements Fetchable {
 	protected String referencedPropertyName;
 	private String referencedEntityName;
 	private String propertyName;
-	private boolean embedded;
 	private boolean lazy = true;
 	protected boolean unwrapProxy;
 	protected boolean referenceToPrimaryKey = true;
@@ -106,8 +105,7 @@ public boolean isSame(SimpleValue other) {
 	public boolean isSame(ToOne other) {
 		return super.isSame( other )
 				&& Objects.equals( referencedPropertyName, other.referencedPropertyName )
-				&& Objects.equals( referencedEntityName, other.referencedEntityName )
-				&& embedded == other.embedded;
+				&& Objects.equals( referencedEntityName, other.referencedEntityName );
 	}
 
 	public boolean isValid(Mapping mapping) throws MappingException {

hibernate-core/src/main/java/org/hibernate/metamodel/model/convert/internal/OrdinalEnumValueConverter.java

@@ -60,7 +60,7 @@ public Integer toRelationalValue(E domainForm) {
 
 	@Override
 	public int getJdbcTypeCode() {
-		return Types.INTEGER;
+		return Types.TINYINT;
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/tool/schema/internal/StandardTableExporter.java

@@ -119,10 +119,9 @@ public String[] getSqlCreateStrings(Table table, Metadata metadata) {
 				);
 			}
 
-			if ( col.getCheckConstraint() != null && dialect.supportsColumnCheck() ) {
-				buf.append( " check (" )
-						.append( col.getCheckConstraint() )
-						.append( ")" );
+			String checkConstraint = col.checkConstraint();
+			if ( checkConstraint != null && dialect.supportsColumnCheck() ) {
+				buf.append( checkConstraint );
 			}
 
 			String columnComment = col.getComment();

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

@@ -227,7 +227,7 @@ private EnumValueConverter interpretParameters(Properties parameters) {
 				return new OrdinalEnumValueConverter(
 						enumJavaDescriptor,
 						integerJavaDescriptor.getJdbcRecommendedSqlType( localIndicators ),
-						(BasicJavaDescriptor) typeConfiguration.getJavaTypeDescriptorRegistry().getDescriptor( Integer.class )
+						typeConfiguration.getJavaTypeDescriptorRegistry().getDescriptor( Integer.class )
 				);
 			}
 		}
@@ -238,7 +238,7 @@ private EnumValueConverter interpretParameters(Properties parameters) {
 				return new OrdinalEnumValueConverter(
 						enumJavaDescriptor,
 						integerJavaDescriptor.getJdbcRecommendedSqlType( localIndicators ),
-						(BasicJavaDescriptor) typeConfiguration.getJavaTypeDescriptorRegistry().getDescriptor( Integer.class )
+						typeConfiguration.getJavaTypeDescriptorRegistry().getDescriptor( Integer.class )
 				);
 			}
 			else if ( isCharacterType( type ) ) {
@@ -263,7 +263,7 @@ else if ( isCharacterType( type ) ) {
 		return new OrdinalEnumValueConverter(
 				enumJavaDescriptor,
 				integerJavaDescriptor.getJdbcRecommendedSqlType( localIndicators ),
-				(BasicJavaDescriptor) typeConfiguration.getJavaTypeDescriptorRegistry().getDescriptor( Integer.class )
+				typeConfiguration.getJavaTypeDescriptorRegistry().getDescriptor( Integer.class )
 		);
 	}
 

hibernate-core/src/main/java/org/hibernate/type/descriptor/java/BooleanTypeDescriptor.java

@@ -9,6 +9,8 @@
 import org.hibernate.dialect.Dialect;
 import org.hibernate.type.descriptor.WrapperOptions;
 import org.hibernate.type.descriptor.java.spi.Primitive;
+import org.hibernate.type.descriptor.sql.BitTypeDescriptor;
+import org.hibernate.type.descriptor.sql.SqlTypeDescriptor;
 
 import static java.lang.Boolean.FALSE;
 import static java.lang.Boolean.TRUE;
@@ -157,4 +159,11 @@ public int getDefaultSqlPrecision(Dialect dialect) {
 	public int getDefaultSqlScale() {
 		return 0;
 	}
+
+	@Override
+	public String getCheckCondition(String columnName, SqlTypeDescriptor sqlTypeDescriptor, Dialect dialect) {
+		return sqlTypeDescriptor instanceof BitTypeDescriptor && !dialect.supportsBitType()
+				? columnName + " in (0,1)"
+				: null;
+	}
 }

hibernate-core/src/main/java/org/hibernate/type/descriptor/java/EnumJavaTypeDescriptor.java

@@ -9,9 +9,13 @@
 import java.sql.Types;
 import javax.persistence.EnumType;
 
+import org.hibernate.dialect.Dialect;
 import org.hibernate.type.descriptor.WrapperOptions;
+import org.hibernate.type.descriptor.sql.IntegerTypeDescriptor;
 import org.hibernate.type.descriptor.sql.SqlTypeDescriptor;
 import org.hibernate.type.descriptor.sql.SqlTypeDescriptorIndicators;
+import org.hibernate.type.descriptor.sql.TinyIntTypeDescriptor;
+import org.hibernate.type.descriptor.sql.VarcharTypeDescriptor;
 
 /**
  * Describes a Java Enum type.
@@ -32,7 +36,7 @@ public SqlTypeDescriptor getJdbcRecommendedSqlType(SqlTypeDescriptorIndicators c
 					: context.getTypeConfiguration().getSqlTypeDescriptorRegistry().getDescriptor( Types.VARCHAR );
 		}
 		else {
-			return context.getTypeConfiguration().getSqlTypeDescriptorRegistry().getDescriptor( Types.INTEGER );
+			return context.getTypeConfiguration().getSqlTypeDescriptorRegistry().getDescriptor( Types.TINYINT );
 		}
 	}
 
@@ -56,7 +60,9 @@ public <X> X unwrap(T value, Class<X> type, WrapperOptions options) {
 		else if ( Integer.class.equals( type ) ) {
 			return (X) toOrdinal( value );
 		}
-
+		else if ( Byte.class.equals( type ) ) {
+			return (X) toByte( value );
+		}
 		return (X) value;
 	}
 
@@ -72,10 +78,22 @@ else if ( value instanceof String ) {
 		else if ( value instanceof Integer ) {
 			return fromOrdinal( (Integer) value );
 		}
+		else if ( value instanceof Byte ) {
+			return fromByte( (Byte) value );
+		}
 
 		return (T) value;
 	}
 
+	/**
+	 * Convert a value of the enum type to its ordinal value
+	 */
+	public <E extends Enum> Byte toByte(E domainForm) {
+		if ( domainForm == null ) {
+			return null;
+		}
+		return (byte) domainForm.ordinal();
+	}
 
 	/**
 	 * Convert a value of the enum type to its ordinal value
@@ -87,6 +105,17 @@ public <E extends Enum> Integer toOrdinal(E domainForm) {
 		return domainForm.ordinal();
 	}
 
+	/**
+	 * Interpret a numeric value as the ordinal of the enum type
+	 */
+	@SuppressWarnings("unchecked")
+	public <E extends Enum> E fromByte(Byte relationalForm) {
+		if ( relationalForm == null ) {
+			return null;
+		}
+		return (E) getJavaType().getEnumConstants()[ relationalForm ];
+	}
+
 	/**
 	 * Interpret a numeric value as the ordinal of the enum type
 	 */
@@ -118,4 +147,24 @@ public T fromName(String relationalForm) {
 		}
 		return (T) Enum.valueOf( getJavaType(), relationalForm.trim() );
 	}
+
+	@Override
+	public String getCheckCondition(String columnName, SqlTypeDescriptor sqlTypeDescriptor, Dialect dialect) {
+		if (sqlTypeDescriptor instanceof TinyIntTypeDescriptor
+				|| sqlTypeDescriptor instanceof IntegerTypeDescriptor) {
+			int last = getJavaType().getEnumConstants().length - 1;
+			return columnName + " between 0 and " + last;
+		}
+		else if (sqlTypeDescriptor instanceof VarcharTypeDescriptor) {
+			StringBuilder types = new StringBuilder();
+			for ( Enum value : getJavaType().getEnumConstants() ) {
+				if (types.length() != 0) {
+					types.append(", ");
+				}
+				types.append("'").append( value.name() ).append("'");
+			}
+			return columnName + " in (" + types + ")";
+		}
+		return null;
+	}
 }

hibernate-core/src/main/java/org/hibernate/type/descriptor/java/JavaTypeDescriptor.java

@@ -186,4 +186,17 @@ default String toString(T value) {
 	 */
 	@Deprecated
 	Class<T> getJavaTypeClass();
+
+	/**
+	 * The check constraint that should be added to the column
+	 * definition in generated DDL.
+	 *
+	 * @param columnName the name of the column
+	 * @param sqlType the {@link SqlTypeDescriptor} of the mapped column
+	 * @param dialect the SQL {@link Dialect}
+	 * @return a check constraint condition or null
+	 */
+	default String getCheckCondition(String columnName, SqlTypeDescriptor sqlType, Dialect dialect) {
+		return null;
+	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/sql/ast/SmokeTests.java

@@ -180,7 +180,7 @@ public void testConvertedHqlInterpretation(SessionFactoryScope scope) {
 					final CustomType basicType = (CustomType) selectedExpressable;
 					final EnumType enumType = (EnumType) basicType.getUserType();
 					assertThat( enumType.getEnumValueConverter().getRelationalJavaDescriptor().getJavaType(), AssignableMatcher.assignableTo( Integer.class ) );
-					assertThat( enumType.sqlTypes()[0], is( Types.INTEGER ) );
+					assertThat( enumType.sqlTypes()[0], is( Types.TINYINT ) );
 
 
 					assertThat( sqlAst.getDomainResultDescriptors().size(), is( 1 ) );