introduce TableMigrator and kill some code duplication

hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java

@@ -45,7 +45,6 @@ import org.hibernate.NotYetImplementedFor6Exception;
 import org.hibernate.ScrollMode;
 import org.hibernate.boot.TempTableDdlTransactionHandling;
 import org.hibernate.boot.model.TypeContributions;
-import org.hibernate.boot.model.convert.spi.ConverterRegistry;
 import org.hibernate.boot.model.relational.AuxiliaryDatabaseObject;
 import org.hibernate.boot.model.relational.Sequence;
 import org.hibernate.boot.spi.SessionFactoryOptions;
@@ -153,7 +152,9 @@ import org.hibernate.tool.schema.internal.StandardIndexExporter;
 import org.hibernate.tool.schema.internal.StandardSequenceExporter;
 import org.hibernate.tool.schema.internal.StandardTableCleaner;
 import org.hibernate.tool.schema.internal.StandardTableExporter;
+import org.hibernate.tool.schema.internal.StandardTableMigrator;
 import org.hibernate.tool.schema.internal.StandardUniqueKeyExporter;
+import org.hibernate.tool.schema.internal.TableMigrator;
 import org.hibernate.tool.schema.spi.Cleaner;
 import org.hibernate.tool.schema.spi.Exporter;
 import org.hibernate.tool.schema.spi.SchemaManagementTool;
@@ -2488,12 +2489,17 @@ public abstract class Dialect implements ConversionContext {
 	private final StandardUniqueKeyExporter uniqueKeyExporter = new StandardUniqueKeyExporter( this );
 	private final StandardAuxiliaryDatabaseObjectExporter auxiliaryObjectExporter = new StandardAuxiliaryDatabaseObjectExporter( this );
 	private final StandardTemporaryTableExporter temporaryTableExporter = new StandardTemporaryTableExporter( this );
+	private final StandardTableMigrator tableMigrator = new StandardTableMigrator( this );
 	private final StandardTableCleaner tableCleaner = new StandardTableCleaner( this );
 
 	public Exporter<Table> getTableExporter() {
 		return tableExporter;
 	}
 
+	public TableMigrator getTableMigrator() {
+		return tableMigrator;
+	}
+
 	public Cleaner getTableCleaner() {
 		return tableCleaner;
 	}

hibernate-core/src/main/java/org/hibernate/internal/util/StringHelper.java

@@ -869,10 +869,11 @@ public final class StringHelper {
 	 * Return the interned form of a String, or null if the parameter is null.
 	 * <p>
 	 * Use with caution: excessive interning is known to cause issues.
-	 * Best to use only with strings which are known to be long lived constants,
+	 * Best to use only with strings which are known to be long-lived constants,
 	 * and for which the chances of being actual duplicates is proven.
 	 * (Even better: avoid needing interning by design changes such as reusing
 	 * the known reference)
+	 *
 	 * @param string The string to intern.
 	 * @return The interned string.
 	 */

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

@@ -31,9 +31,9 @@ import org.hibernate.boot.model.relational.QualifiedTableName;
 import org.hibernate.boot.model.relational.SqlStringGenerationContext;
 import org.hibernate.boot.spi.InFlightMetadataCollector;
 import org.hibernate.dialect.Dialect;
-import org.hibernate.tool.schema.extract.spi.ColumnInformation;
 import org.hibernate.tool.schema.extract.spi.TableInformation;
 
+import org.hibernate.tool.schema.internal.StandardTableMigrator;
 import org.jboss.logging.Logger;
 
 import static java.util.Collections.unmodifiableList;
@@ -160,6 +160,14 @@ public class Table implements Serializable, ContributableDatabaseObject {
 		return name;
 	}
 
+	public Identifier getSchemaIdentifier() {
+		return schema;
+	}
+
+	public Identifier getCatalogIdentifier() {
+		return catalog;
+	}
+
 	public String getQuotedName() {
 		return name == null ? null : name.toString();
 	}
@@ -432,88 +440,14 @@ public class Table implements Serializable, ContributableDatabaseObject {
 		}
 	}
 
+	@Deprecated(since = "6.2") @Remove
 	public Iterator<String> sqlAlterStrings(
 			Dialect dialect,
 			Metadata metadata,
 			TableInformation tableInfo,
 			SqlStringGenerationContext sqlStringGenerationContext) throws HibernateException {
-		final String tableName = sqlStringGenerationContext.format( new QualifiedTableName( catalog, schema, name ) );
+		return StandardTableMigrator.sqlAlterStrings(this, dialect, metadata, tableInfo, sqlStringGenerationContext )
-
+				.iterator();
-		final StringBuilder root = new StringBuilder( dialect.getAlterTableString( tableName ) )
-				.append( ' ' )
-				.append( dialect.getAddColumnString() );
-
-		final List<String> results = new ArrayList<>();
-
-		for ( Column column : getColumns() ) {
-			final ColumnInformation columnInfo = tableInfo.getColumn(
-					Identifier.toIdentifier( column.getName(), column.isQuoted() )
-			);
-
-			if ( columnInfo == null ) {
-				// the column doesn't exist at all.
-				final StringBuilder alter = new StringBuilder( root.toString() )
-						.append( ' ' )
-						.append( column.getQuotedName( dialect ) );
-
-				final String columnType = column.getSqlType(
-						metadata.getDatabase().getTypeConfiguration(),
-						dialect,
-						metadata
-				);
-				if ( column.hasSpecializedTypeDeclaration() ) {
-					alter.append( ' ' ).append( column.getSpecializedTypeDeclaration() );
-				}
-				else if ( column.getGeneratedAs() == null || dialect.hasDataTypeBeforeGeneratedAs() ) {
-					alter.append(' ').append(columnType);
-				}
-
-				final String defaultValue = column.getDefaultValue();
-				if ( defaultValue != null ) {
-					alter.append( " default " ).append( defaultValue );
-				}
-
-				final String generatedAs = column.getGeneratedAs();
-				if ( generatedAs != null) {
-					alter.append( dialect.generatedAs( generatedAs ) );
-				}
-
-				if ( column.isNullable() ) {
-					alter.append( dialect.getNullColumnString( columnType ) );
-				}
-				else {
-					alter.append( " not null" );
-				}
-
-				if ( column.isUnique() && !isPrimaryKey( column ) ) {
-					String keyName = Constraint.generateName( "UK_", this, column );
-					UniqueKey uk = getOrCreateUniqueKey( keyName );
-					uk.addColumn( column );
-					alter.append( dialect.getUniqueDelegate()
-							.getColumnDefinitionUniquenessFragment( column, sqlStringGenerationContext ) );
-				}
-
-				if ( column.hasCheckConstraint() && dialect.supportsColumnCheck() ) {
-					alter.append( column.checkConstraint() );
-				}
-
-				final String columnComment = column.getComment();
-				if ( columnComment != null ) {
-					alter.append( dialect.getColumnComment( columnComment ) );
-				}
-
-				alter.append( dialect.getAddColumnSuffixString() );
-
-				results.add( alter.toString() );
-			}
-
-		}
-
-		if ( results.isEmpty() ) {
-			log.debugf( "No alter strings for table : %s", getQuotedName() );
-		}
-
-		return results.iterator();
 	}
 
 	public boolean isPrimaryKey(Column column) {

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

@@ -186,14 +186,14 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 		final Set<String> exportIdentifiers = CollectionHelper.setOfSize( 50 );
 
 		final Database database = metadata.getDatabase();
+		Exporter<AuxiliaryDatabaseObject> auxiliaryExporter = dialect.getAuxiliaryDatabaseObjectExporter();
 
 		// Drop all AuxiliaryDatabaseObjects
 		for ( AuxiliaryDatabaseObject auxiliaryDatabaseObject : database.getAuxiliaryDatabaseObjects() ) {
 			if ( auxiliaryDatabaseObject.appliesToDialect( dialect ) ) {
 				applySqlStrings(
 						true,
-						dialect.getAuxiliaryDatabaseObjectExporter()
+						auxiliaryExporter.getSqlDropStrings( auxiliaryDatabaseObject, metadata, sqlGenerationContext ),
-								.getSqlDropStrings( auxiliaryDatabaseObject, metadata, sqlGenerationContext ),
 						formatter,
 						options,
 						targets
@@ -207,7 +207,7 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 					&& auxiliaryDatabaseObject.appliesToDialect( dialect ) ) {
 				applySqlStrings(
 						true,
-						auxiliaryDatabaseObject.sqlCreateStrings( sqlGenerationContext ),
+						auxiliaryExporter.getSqlCreateStrings( auxiliaryDatabaseObject, metadata, sqlGenerationContext ),
 						formatter,
 						options,
 						targets
@@ -246,18 +246,10 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 			if ( options.getSchemaFilter().includeNamespace( namespace ) ) {
 				for ( Sequence sequence : namespace.getSequences() ) {
 					if ( contributableInclusionFilter.matches( sequence ) ) {
-						checkExportIdentifier( sequence, exportIdentifiers );
+						checkExportIdentifier( sequence, exportIdentifiers);
-						final SequenceInformation sequenceInformation =
+						final SequenceInformation sequenceInformation = existingDatabase.getSequenceInformation( sequence.getName() );
-								existingDatabase.getSequenceInformation( sequence.getName() );
 						if ( sequenceInformation == null ) {
-							applySqlStrings(
+							applySequence( sequence, dialect, metadata, formatter, options, sqlGenerationContext, targets );
-									false,
-									dialect.getSequenceExporter()
-											.getSqlCreateStrings( sequence, metadata, sqlGenerationContext ),
-									formatter,
-									options,
-									targets
-							);
 						}
 					}
 				}
@@ -269,17 +261,12 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 			if ( options.getSchemaFilter().includeNamespace( namespace ) ) {
 				final NameSpaceTablesInformation nameSpaceTablesInformation = tablesInformation.get( namespace );
 				for ( Table table : namespace.getTables() ) {
-					if ( ! options.getSchemaFilter().includeTable( table ) ) {
+					if ( options.getSchemaFilter().includeTable( table ) && contributableInclusionFilter.matches( table ) ) {
-						continue;
+						final TableInformation tableInformation = nameSpaceTablesInformation.getTableInformation( table );
-					}
+						if ( tableInformation == null || tableInformation.isPhysicalTable() ) {
-					if ( ! contributableInclusionFilter.matches( table ) ) {
+							applyForeignKeys( table, tableInformation, dialect, metadata, formatter, options,
-						continue;
+										sqlGenerationContext, targets );
-					}
+						}
-
-					final TableInformation tableInformation = nameSpaceTablesInformation.getTableInformation( table );
-					if ( tableInformation == null || tableInformation.isPhysicalTable() ) {
-						applyForeignKeys( table, tableInformation, dialect, metadata, formatter, options,
-									sqlGenerationContext, targets );
 					}
 				}
 			}
@@ -287,10 +274,10 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 
 		// Create after-table AuxiliaryDatabaseObjects
 		for ( AuxiliaryDatabaseObject auxiliaryDatabaseObject : database.getAuxiliaryDatabaseObjects() ) {
-			if ( auxiliaryDatabaseObject.beforeTablesOnCreation() && auxiliaryDatabaseObject.appliesToDialect( dialect )) {
+			if ( auxiliaryDatabaseObject.beforeTablesOnCreation() && auxiliaryDatabaseObject.appliesToDialect( dialect ) ) {
 				applySqlStrings(
 						true,
-						auxiliaryDatabaseObject.sqlCreateStrings( sqlGenerationContext ),
+						auxiliaryExporter.getSqlCreateStrings( auxiliaryDatabaseObject, metadata, sqlGenerationContext ),
 						formatter,
 						options,
 						targets
@@ -299,6 +286,23 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 		}
 	}
 
+	private static void applySequence(
+			Sequence sequence,
+			Dialect dialect,
+			Metadata metadata,
+			Formatter formatter,
+			ExecutionOptions options,
+			SqlStringGenerationContext sqlGenerationContext,
+			GenerationTarget... targets) {
+		applySqlStrings(
+				false,
+				dialect.getSequenceExporter().getSqlCreateStrings( sequence, metadata, sqlGenerationContext ),
+				formatter,
+				options,
+				targets
+		);
+	}
+
 	protected void createTable(
 			Table table,
 			Dialect dialect,
@@ -327,12 +331,8 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 			GenerationTarget... targets) {
 		applySqlStrings(
 				false,
-				table.sqlAlterStrings(
+				dialect.getTableMigrator()
-						dialect,
+						.getSqlAlterStrings( table, metadata, tableInformation, sqlGenerationContext ),
-						metadata,
-						tableInformation,
-						sqlGenerationContext
-				),
 				formatter,
 				options,
 				targets
@@ -576,17 +576,4 @@ public abstract class AbstractSchemaMigrator implements SchemaMigrator {
 			}
 		}
 	}
-
-	private static void applySqlStrings(
-			boolean quiet,
-			Iterator<String> sqlStrings,
-			Formatter formatter,
-			ExecutionOptions options,
-			GenerationTarget... targets) {
-		if ( sqlStrings != null ) {
-			while ( sqlStrings.hasNext() ) {
-				applySqlString( quiet, sqlStrings.next(), formatter, options, targets );
-			}
-		}
-	}
 }

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

@@ -6,6 +6,7 @@
  */
 package org.hibernate.tool.schema.internal;
 
+import org.hibernate.Incubating;
 import org.hibernate.boot.Metadata;
 import org.hibernate.boot.model.naming.Identifier;
 import org.hibernate.boot.model.relational.QualifiedNameParser;
@@ -24,6 +25,7 @@ import java.util.stream.Collectors;
  *
  * @author Gavin King
  */
+@Incubating
 public class StandardTableCleaner implements Cleaner {
 	protected final Dialect dialect;
 

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

@@ -7,7 +7,6 @@
 package org.hibernate.tool.schema.internal;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import org.hibernate.MappingException;
@@ -20,19 +19,22 @@ import org.hibernate.boot.model.relational.QualifiedTableName;
 import org.hibernate.boot.model.relational.SqlStringGenerationContext;
 import org.hibernate.boot.spi.MetadataImplementor;
 import org.hibernate.dialect.Dialect;
-import org.hibernate.internal.util.StringHelper;
 import org.hibernate.mapping.Column;
 import org.hibernate.mapping.Constraint;
 import org.hibernate.mapping.Table;
 import org.hibernate.mapping.UniqueKey;
 import org.hibernate.tool.schema.spi.Exporter;
 
+import static java.util.Collections.addAll;
+import static org.hibernate.internal.util.StringHelper.EMPTY_STRINGS;
+
 /**
  * An {@link Exporter} for {@linkplain Table tables}.
  *
  * @author Steve Ebersole
  */
 public class StandardTableExporter implements Exporter<Table> {
+
 	protected final Dialect dialect;
 
 	public StandardTableExporter(Dialect dialect) {
@@ -44,39 +46,17 @@ public class StandardTableExporter implements Exporter<Table> {
 			Table table,
 			Metadata metadata,
 			SqlStringGenerationContext context) {
-		final QualifiedName tableName = new QualifiedNameParser.NameParts(
+		final QualifiedName tableName = getTableName(table);
-				Identifier.toIdentifier( table.getCatalog(), table.isCatalogQuoted() ),
-				Identifier.toIdentifier( table.getSchema(), table.isSchemaQuoted() ),
-				table.getNameIdentifier()
-		);
 
 		try {
-			String formattedTableName = context.format( tableName );
+			final String formattedTableName = context.format( tableName );
-			StringBuilder createTable =
+
+			final StringBuilder createTable =
 					new StringBuilder( tableCreateString( table.hasPrimaryKey() ) )
 							.append( ' ' )
 							.append( formattedTableName )
 							.append( " (" );
 
-
-			boolean isPrimaryKeyIdentity = table.hasPrimaryKey()
-					&& table.getIdentifierValue() != null
-					&& table.getIdentifierValue().isIdentityColumn(
-							( (MetadataImplementor) metadata ).getMetadataBuildingOptions()
-									.getIdentifierGeneratorFactory(),
-							dialect
-					);
-			// TODO: this is the much better form moving forward as we move to metamodel
-			//boolean isPrimaryKeyIdentity = hasPrimaryKey
-			//				&& table.getPrimaryKey().getColumnSpan() == 1
-			//				&& table.getPrimaryKey().getColumn( 0 ).isIdentity();
-
-			// Try to find out the name of the primary key in case the dialect needs it to create an identity
-			String pkColName = null;
-			if ( table.hasPrimaryKey() ) {
-				pkColName = table.getPrimaryKey().getColumns().get(0).getQuotedName( dialect );
-			}
-
 			boolean isFirst = true;
 			for ( Column column : table.getColumns() ) {
 				if ( isFirst ) {
@@ -85,75 +65,10 @@ public class StandardTableExporter implements Exporter<Table> {
 				else {
 					createTable.append( ", " );
 				}
-
+				appendColumn( createTable, column, table, metadata, dialect, context );
-				String colName = column.getQuotedName( dialect );
-				createTable.append( colName );
-
-				if ( isPrimaryKeyIdentity && colName.equals( pkColName ) ) {
-					// to support dialects that have their own identity data type
-					if ( dialect.getIdentityColumnSupport().hasDataTypeInIdentityColumn() ) {
-						createTable.append( ' ' ).append(
-								column.getSqlType( metadata.getDatabase().getTypeConfiguration(), dialect, metadata )
-						);
-					}
-					String identityColumnString = dialect.getIdentityColumnSupport()
-							.getIdentityColumnString( column.getSqlTypeCode(metadata) );
-					createTable.append( ' ' ).append( identityColumnString );
-				}
-				else {
-					final String columnType = column.getSqlType(
-							metadata.getDatabase().getTypeConfiguration(),
-							dialect,
-							metadata
-					);
-					if ( column.hasSpecializedTypeDeclaration() ) {
-						createTable.append( ' ' ).append( column.getSpecializedTypeDeclaration() );
-					}
-					else if ( column.getGeneratedAs() == null || dialect.hasDataTypeBeforeGeneratedAs() ) {
-						createTable.append( ' ' ).append( columnType );
-					}
-
-					String defaultValue = column.getDefaultValue();
-					if ( defaultValue != null ) {
-						createTable.append( " default " ).append( defaultValue );
-					}
-
-					String generatedAs = column.getGeneratedAs();
-					if ( generatedAs != null) {
-						createTable.append( dialect.generatedAs( generatedAs ) );
-					}
-
-					if ( column.isNullable() ) {
-						createTable.append( dialect.getNullColumnString( columnType ) );
-					}
-					else {
-						createTable.append( " not null" );
-					}
-
-				}
-
-				if ( column.isUnique() && !table.isPrimaryKey( column ) ) {
-					String keyName = Constraint.generateName( "UK_", table, column );
-					UniqueKey uk = table.getOrCreateUniqueKey( keyName );
-					uk.addColumn( column );
-					createTable.append(
-							dialect.getUniqueDelegate()
-									.getColumnDefinitionUniquenessFragment( column, context )
-					);
-				}
-
-				if ( dialect.supportsColumnCheck() && column.hasCheckConstraint() ) {
-					createTable.append( column.checkConstraint() );
-				}
-
-				String columnComment = column.getComment();
-				if ( columnComment != null ) {
-					createTable.append( dialect.getColumnComment( columnComment ) );
-				}
 			}
 			if ( table.hasPrimaryKey() ) {
-				createTable.append( ", " )
+				createTable.append( ", " ).append( table.getPrimaryKey().sqlConstraintString( dialect ) );
-						.append( table.getPrimaryKey().sqlConstraintString( dialect ) );
 			}
 
 			createTable.append( dialect.getUniqueDelegate().getTableCreationUniqueConstraintsFragment( table, context ) );
@@ -168,20 +83,108 @@ public class StandardTableExporter implements Exporter<Table> {
 
 			applyTableTypeString( createTable );
 
-			List<String> sqlStrings = new ArrayList<>();
+			final List<String> sqlStrings = new ArrayList<>();
 			sqlStrings.add( createTable.toString() );
-
 			applyComments( table, formattedTableName, sqlStrings );
-
 			applyInitCommands( table, sqlStrings, context );
-
+			return sqlStrings.toArray( EMPTY_STRINGS );
-			return sqlStrings.toArray(StringHelper.EMPTY_STRINGS);
 		}
 		catch (Exception e) {
 			throw new MappingException( "Error creating SQL create commands for table : " + tableName, e );
 		}
 	}
 
+	static void appendColumn(
+			StringBuilder statement,
+			Column column,
+			Table table,
+			Metadata metadata,
+			Dialect dialect,
+			SqlStringGenerationContext context) {
+
+		statement.append( column.getQuotedName( dialect ) );
+
+		final String columnType = column.getSqlType( metadata.getDatabase().getTypeConfiguration(), dialect, metadata );
+		if ( isIdentityColumn( column, table, metadata, dialect ) ) {
+			// to support dialects that have their own identity data type
+			if ( dialect.getIdentityColumnSupport().hasDataTypeInIdentityColumn() ) {
+				statement.append( ' ' ).append( columnType );
+			}
+			final String identityColumnString = dialect.getIdentityColumnSupport()
+					.getIdentityColumnString( column.getSqlTypeCode( metadata ) );
+			statement.append( ' ' ).append( identityColumnString );
+		}
+		else {
+			if ( column.hasSpecializedTypeDeclaration() ) {
+				statement.append( ' ' ).append( column.getSpecializedTypeDeclaration() );
+			}
+			else if ( column.getGeneratedAs() == null || dialect.hasDataTypeBeforeGeneratedAs() ) {
+				statement.append( ' ' ).append( columnType );
+			}
+
+			final String defaultValue = column.getDefaultValue();
+			if ( defaultValue != null ) {
+				statement.append( " default " ).append( defaultValue );
+			}
+
+			final String generatedAs = column.getGeneratedAs();
+			if ( generatedAs != null) {
+				statement.append( dialect.generatedAs( generatedAs ) );
+			}
+
+			if ( column.isNullable() ) {
+				statement.append( dialect.getNullColumnString(columnType) );
+			}
+			else {
+				statement.append( " not null" );
+			}
+		}
+
+		if ( column.isUnique() && !table.isPrimaryKey(column) ) {
+			final String keyName = Constraint.generateName( "UK_", table, column);
+			final UniqueKey uk = table.getOrCreateUniqueKey( keyName );
+			uk.addColumn(column);
+			statement.append(
+					dialect.getUniqueDelegate().getColumnDefinitionUniquenessFragment( column, context )
+			);
+		}
+
+		if ( dialect.supportsColumnCheck() && column.hasCheckConstraint() ) {
+			statement.append( column.checkConstraint() );
+		}
+
+		final String columnComment = column.getComment();
+		if ( columnComment != null ) {
+			statement.append( dialect.getColumnComment( columnComment ) );
+		}
+	}
+
+	private static boolean isIdentityColumn(Column column, Table table, Metadata metadata, Dialect dialect) {
+		// Try to find out the name of the primary key in case the dialect needs it to create an identity
+		return isPrimaryKeyIdentity( table, metadata, dialect )
+			&& column.getQuotedName( dialect ).equals( getPrimaryKeyColumnName( table, dialect ) );
+	}
+
+	private static String getPrimaryKeyColumnName(Table table, Dialect dialect) {
+		return table.hasPrimaryKey()
+				? table.getPrimaryKey().getColumns().get(0).getQuotedName( dialect )
+				: null;
+	}
+
+	private static boolean isPrimaryKeyIdentity(Table table, Metadata metadata, Dialect dialect) {
+		// TODO: this is the much better form moving forward as we move to metamodel
+		//return hasPrimaryKey
+		//				&& table.getPrimaryKey().getColumnSpan() == 1
+		//				&& table.getPrimaryKey().getColumn( 0 ).isIdentity();
+		MetadataImplementor metadataImplementor = (MetadataImplementor) metadata;
+		return table.hasPrimaryKey()
+			&& table.getIdentifierValue() != null
+			&& table.getIdentifierValue().isIdentityColumn(
+					metadataImplementor.getMetadataBuildingOptions().getIdentifierGeneratorFactory(),
+					dialect
+			);
+	}
+
 	/**
 	 * @param table The table.
 	 * @param tableName The qualified table name.
@@ -202,12 +205,16 @@ public class StandardTableExporter implements Exporter<Table> {
 	protected void applyComments(Table table, String formattedTableName, List<String> sqlStrings) {
 		if ( dialect.supportsCommentOn() ) {
 			if ( table.getComment() != null ) {
-				sqlStrings.add( "comment on table " + formattedTableName + " is '" + table.getComment() + "'" );
+				sqlStrings.add( "comment on table "
+						+ formattedTableName
+						+ " is '" + table.getComment() + "'" );
 			}
 			for ( Column column : table.getColumns() ) {
 				String columnComment = column.getComment();
 				if ( columnComment != null ) {
-					sqlStrings.add( "comment on column " + formattedTableName + '.' + column.getQuotedName( dialect ) + " is '" + columnComment + "'" );
+					sqlStrings.add( "comment on column "
+							+ formattedTableName + '.' + column.getQuotedName( dialect )
+							+ " is '" + columnComment + "'" );
 				}
 			}
 		}
@@ -215,7 +222,7 @@ public class StandardTableExporter implements Exporter<Table> {
 
 	protected void applyInitCommands(Table table, List<String> sqlStrings, SqlStringGenerationContext context) {
 		for ( InitCommand initCommand : table.getInitCommands( context ) ) {
-			Collections.addAll( sqlStrings, initCommand.getInitCommands() );
+			addAll( sqlStrings, initCommand.getInitCommands() );
 		}
 	}
 
@@ -226,9 +233,7 @@ public class StandardTableExporter implements Exporter<Table> {
 	protected void applyTableCheck(Table table, StringBuilder buf) {
 		if ( dialect.supportsTableCheck() ) {
 			for (String constraint : table.getCheckConstraints() ) {
-				buf.append( ", check (" )
+				buf.append( ", check (" ).append( constraint ).append( ')' );
-						.append( constraint )
-						.append( ')' );
 			}
 		}
 	}
@@ -244,19 +249,19 @@ public class StandardTableExporter implements Exporter<Table> {
 		if ( dialect.supportsIfExistsBeforeTableName() ) {
 			buf.append( "if exists " );
 		}
+		buf.append( context.format( getTableName( table ) ) )
+				.append( dialect.getCascadeConstraintsString() );
+		if ( dialect.supportsIfExistsAfterTableName() ) {
+			buf.append( " if exists" );
+		}
+		return new String[] { buf.toString() };
+	}
 
-		final QualifiedName tableName = new QualifiedNameParser.NameParts(
+	private static QualifiedName getTableName(Table table) {
+		return new QualifiedNameParser.NameParts(
 				Identifier.toIdentifier( table.getCatalog(), table.isCatalogQuoted() ),
 				Identifier.toIdentifier( table.getSchema(), table.isSchemaQuoted() ),
 				table.getNameIdentifier()
 		);
-		buf.append( context.format( tableName ) )
-				.append( dialect.getCascadeConstraintsString() );
-
-		if ( dialect.supportsIfExistsAfterTableName() ) {
-			buf.append( " if exists" );
-		}
-
-		return new String[] { buf.toString() };
 	}
 }

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

@@ -0,0 +1,94 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.tool.schema.internal;
+
+import org.hibernate.HibernateException;
+import org.hibernate.Incubating;
+import org.hibernate.Internal;
+import org.hibernate.boot.Metadata;
+import org.hibernate.boot.model.naming.Identifier;
+import org.hibernate.boot.model.relational.QualifiedTableName;
+import org.hibernate.boot.model.relational.SqlStringGenerationContext;
+import org.hibernate.dialect.Dialect;
+import org.hibernate.mapping.Column;
+import org.hibernate.mapping.Table;
+import org.hibernate.tool.schema.extract.spi.ColumnInformation;
+import org.hibernate.tool.schema.extract.spi.TableInformation;
+import org.jboss.logging.Logger;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.hibernate.internal.util.collections.ArrayHelper.EMPTY_STRING_ARRAY;
+import static org.hibernate.tool.schema.internal.StandardTableExporter.appendColumn;
+
+/**
+ * A {@link TableMigrator} that only knows how to add new columns.
+ *
+ * @author Gavin King
+ */
+@Incubating
+public class StandardTableMigrator implements TableMigrator {
+
+	private static final Logger log = Logger.getLogger( Table.class );
+
+	protected final Dialect dialect;
+
+	public StandardTableMigrator(Dialect dialect) {
+		this.dialect = dialect;
+	}
+
+	@Override
+	public String[] getSqlAlterStrings(
+			Table table,
+			Metadata metadata,
+			TableInformation tableInfo,
+			SqlStringGenerationContext sqlStringGenerationContext) {
+		return sqlAlterStrings( table, dialect, metadata, tableInfo, sqlStringGenerationContext )
+				.toArray( EMPTY_STRING_ARRAY );
+	}
+
+	@Internal
+	public static List<String> sqlAlterStrings(
+			Table table,
+			Dialect dialect,
+			Metadata metadata,
+			TableInformation tableInfo,
+			SqlStringGenerationContext sqlStringGenerationContext) throws HibernateException {
+
+		final String tableName = sqlStringGenerationContext.format( new QualifiedTableName(
+				Identifier.toIdentifier( table.getCatalog(), table.isCatalogQuoted() ),
+				Identifier.toIdentifier( table.getSchema(), table.isSchemaQuoted() ),
+				table.getNameIdentifier() )
+		);
+
+		final StringBuilder root = new StringBuilder( dialect.getAlterTableString( tableName ) )
+				.append( ' ' )
+				.append( dialect.getAddColumnString() );
+
+		final List<String> results = new ArrayList<>();
+
+		for ( Column column : table.getColumns() ) {
+			final ColumnInformation columnInfo = tableInfo.getColumn(
+					Identifier.toIdentifier( column.getName(), column.isQuoted() )
+			);
+			if ( columnInfo == null ) {
+				// the column doesn't exist at all.
+				final StringBuilder alterTable = new StringBuilder( root.toString() ).append( ' ' );
+				appendColumn( alterTable, column, table, metadata, dialect, sqlStringGenerationContext );
+				alterTable.append( dialect.getAddColumnSuffixString() );
+				results.add( alterTable.toString() );
+			}
+		}
+
+		if ( results.isEmpty() ) {
+			log.debugf( "No alter strings for table : %s", table.getQuotedName() );
+		}
+
+		return results;
+	}
+}

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

@@ -0,0 +1,28 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.tool.schema.internal;
+
+import org.hibernate.boot.Metadata;
+import org.hibernate.boot.model.relational.SqlStringGenerationContext;
+import org.hibernate.mapping.Table;
+import org.hibernate.tool.schema.extract.spi.TableInformation;
+
+/**
+ * An object that produces an {@code alter table} statements
+ * needed to update the definition of a table.
+ *
+ * @author Gavin King
+ *
+ * @since 6.2
+ */
+public interface TableMigrator {
+	String[] getSqlAlterStrings(
+			Table table,
+			Metadata metadata,
+			TableInformation tableInfo,
+			SqlStringGenerationContext sqlStringGenerationContext);
+}

hibernate-core/src/main/java/org/hibernate/tool/schema/spi/Cleaner.java

@@ -18,6 +18,8 @@ import java.util.Collection;
  * An object that produces the SQL required to truncate the tables in a schema.
  *
  * @author Gavin King
+ *
+ * @since 6.2
  */
 @Incubating
 public interface Cleaner {