public boolean matches(ForeignKey fk) {
	if ( refTable.equalsIgnoreCase( fk.getReferencedTable().getName() ) ) {
		if ( fk.getColumnSpan() == references.size() ) {
			List fkRefs;
			if ( fk.isReferenceToPrimaryKey() ) {
				fkRefs = fk.getReferencedTable().getPrimaryKey().getColumns();
			}
			else {
				fkRefs = fk.getReferencedColumns();
			}
			for ( int i = 0; i < fk.getColumnSpan(); i++ ) {
				Column column = fk.getColumn( i );
				Column ref = ( Column ) fkRefs.get( i );
				if ( !hasReference( column, ref ) ) {
					return false;
				}
			}
			return true;
		}
	}
	return false;
}
 

@Override
public String[] getSqlDropStrings(ForeignKey foreignKey, Metadata metadata) {
	if ( !dialect.hasAlterTable() ) {
		return NO_COMMANDS;
	}

	if ( !foreignKey.isCreationEnabled() ) {
		return NO_COMMANDS;
	}

	if ( !foreignKey.isPhysicalConstraint() ) {
		return NO_COMMANDS;
	}

	final JdbcEnvironment jdbcEnvironment = metadata.getDatabase().getJdbcEnvironment();
	final String sourceTableName = jdbcEnvironment.getQualifiedObjectNameFormatter().format(
			foreignKey.getTable().getQualifiedTableName(),
			dialect
	);
	return new String[] {
			getSqlDropStrings( sourceTableName, foreignKey, dialect )
	};
}
 

public void testForeignKeyCreation() {
	PersistentClass classMapping = getCfg().getClassMapping("org.hibernate.test.propertyref.basic.Account");
	
	Iterator foreignKeyIterator = classMapping.getTable().getForeignKeyIterator();
	boolean found = false;
	while ( foreignKeyIterator.hasNext() ) {
		ForeignKey element = (ForeignKey) foreignKeyIterator.next();
		if(element.getReferencedEntityName().equals(Person.class.getName() ) ) {
			
			if(!element.isReferenceToPrimaryKey() ) {
				List referencedColumns = element.getReferencedColumns();
				Column column = (Column) referencedColumns.get(0);
				if(column.getName().equals("person_userid") ) {
					found = true; // extend test to include the columns
				}				
			}
		}
	}
	
	assertTrue("Property ref foreign key not found",found);
}
 

@Override
public String[] getSqlDropStrings(ForeignKey foreignKey, Metadata metadata) {
  if (spannerDatabaseInfo == null) {
    throw new IllegalStateException(
        "Cannot determine which foreign keys to drop because spannerDatabaseInfo was null.");
  }

  if (foreignKeyExists(foreignKey)) {
    return super.getSqlDropStrings(foreignKey, metadata);
  } else {
    return new String[0];
  }
}
 

public ForeignKeyMetadata getForeignKeyMetadata(ForeignKey fk) {
	for ( ForeignKeyMetadata existingFk : foreignKeys.values() ) {
		if ( existingFk.matches( fk ) ) {
			return existingFk;
		}
	}
	return null;
}
 

private String getSqlDropStrings(String tableName, ForeignKey foreignKey, Dialect dialect) {
	final StringBuilder buf = new StringBuilder( dialect.getAlterTableString( tableName ) );
	buf.append( dialect.getDropForeignKeyString() );
	if ( dialect.supportsIfExistsBeforeConstraintName() ) {
		buf.append( "if exists " );
	}
	buf.append( dialect.quote( foreignKey.getName() ) );
	if ( dialect.supportsIfExistsAfterConstraintName() ) {
		buf.append( " if exists" );
	}
	return buf.toString();
}
 

protected void applyForeignKeys(
		Table table,
		TableInformation tableInformation,
		Dialect dialect,
		Metadata metadata,
		Formatter formatter,
		ExecutionOptions options,
		GenerationTarget... targets) {
	if ( dialect.hasAlterTable() ) {
		final Exporter<ForeignKey> exporter = dialect.getForeignKeyExporter();

		@SuppressWarnings("unchecked")
		final Iterator<ForeignKey> fkItr = table.getForeignKeyIterator();
		while ( fkItr.hasNext() ) {
			final ForeignKey foreignKey = fkItr.next();
			if ( foreignKey.isPhysicalConstraint() && foreignKey.isCreationEnabled() ) {
				boolean existingForeignKeyFound = false;
				if ( tableInformation != null ) {
					existingForeignKeyFound = checkForExistingForeignKey(
							foreignKey,
							tableInformation
					);
				}
				if ( !existingForeignKeyFound ) {
					// todo : shouldn't we just drop+recreate if FK exists?
					//		this follows the existing code from legacy SchemaUpdate which just skipped

					// in old SchemaUpdate code, this was the trigger to "create"
					applySqlStrings(
							false,
							exporter.getSqlCreateStrings( foreignKey, metadata ),
							formatter,
							options,
							targets
					);
				}
			}
		}
	}
}
 

/**
 * Check if the ForeignKey already exists. First check based on definition and if that is not matched check if a key
 * with the exact same name exists. Keys with the same name are presumed to be functional equal.
 * 
 * @param foreignKey - ForeignKey, new key to be created
 * @param tableInformation - TableInformation, information of existing keys
 * @return boolean, true if key already exists
 */
private boolean checkForExistingForeignKey(ForeignKey foreignKey, TableInformation tableInformation) {
	if ( foreignKey.getName() == null || tableInformation == null ) {
		return false;
	}

	final String referencingColumn = foreignKey.getColumn( 0 ).getName();
	final String referencedTable = foreignKey.getReferencedTable().getName();

	/*
	 * Find existing keys based on referencing column and referencedTable. "referencedColumnName" is not checked
	 * because that always is the primary key of the "referencedTable".
	 */
	Predicate<ColumnReferenceMapping> mappingPredicate = m -> {
		String existingReferencingColumn = m.getReferencingColumnMetadata().getColumnIdentifier().getText();
		String existingReferencedTable = m.getReferencedColumnMetadata().getContainingTableInformation().getName().getTableName().getCanonicalName();
		return referencingColumn.equals( existingReferencingColumn ) && referencedTable.equals( existingReferencedTable );
	};
	Stream<ForeignKeyInformation> keyStream = StreamSupport.stream( tableInformation.getForeignKeys().spliterator(), false );
	Stream<ColumnReferenceMapping> mappingStream = keyStream.flatMap( k -> StreamSupport.stream( k.getColumnReferenceMappings().spliterator(), false ) );
	boolean found = mappingStream.anyMatch( mappingPredicate );
	if ( found ) {
		return true;
	}

	// And at the end just compare the name of the key. If a key with the same name exists we assume the function is
	// also the same...
	return tableInformation.getForeignKey( Identifier.toIdentifier( foreignKey.getName() ) ) != null;
}
 

private void applyConstraintDropping(
		Namespace namespace,
		Metadata metadata,
		Formatter formatter,
		ExecutionOptions options,
		GenerationTarget... targets) {
	final Dialect dialect = metadata.getDatabase().getJdbcEnvironment().getDialect();

	if ( !dialect.dropConstraints() ) {
		return;
	}

	for ( Table table : namespace.getTables() ) {
		if ( !table.isPhysicalTable() ) {
			continue;
		}
		if ( !schemaFilter.includeTable( table ) ) {
			continue;
		}

		final Iterator fks = table.getForeignKeyIterator();
		while ( fks.hasNext() ) {
			final ForeignKey foreignKey = (ForeignKey) fks.next();
			applySqlStrings(
					dialect.getForeignKeyExporter().getSqlDropStrings( foreignKey, metadata ),
					formatter,
					options,
					targets
			);
		}
	}
}
 

private void secondPassCompileForeignKeys(MetadataBuildingContext buildingContext) {
	int uniqueInteger = 0;
	Set<ForeignKey> done = new HashSet<>();
	for ( Table table : collectTableMappings() ) {
		table.setUniqueInteger( uniqueInteger++ );
		secondPassCompileForeignKeys( table, done, buildingContext );
	}
}
 

protected void secondPassCompileForeignKeys(Table table, Set done) throws MappingException {

		table.createForeignKeys();

		Iterator iter = table.getForeignKeyIterator();
		while ( iter.hasNext() ) {

			ForeignKey fk = (ForeignKey) iter.next();
			if ( !done.contains( fk ) ) {
				done.add( fk );
				final String referencedEntityName = fk.getReferencedEntityName();
				if ( referencedEntityName == null ) {
					throw new MappingException(
							"An association from the table " +
							fk.getTable().getName() +
							" does not specify the referenced entity"
						);
				}
				if ( log.isDebugEnabled() ) {
					log.debug( "resolving reference to class: " + referencedEntityName );
				}
				PersistentClass referencedClass = (PersistentClass) classes.get( referencedEntityName );
				if ( referencedClass == null ) {
					throw new MappingException(
							"An association from the table " +
							fk.getTable().getName() +
							" refers to an unmapped class: " +
							referencedEntityName
						);
				}
				if ( referencedClass.isJoinedSubclass() ) {
					secondPassCompileForeignKeys( referencedClass.getSuperclass().getTable(), done );
				}
				fk.setReferencedTable( referencedClass.getTable() );
				fk.alignColumns();
			}
		}
	}
 

@Override
public Exporter<ForeignKey> getForeignKeyExporter() {
  return this.spannerForeignKeyExporter;
}
 

private boolean foreignKeyExists(ForeignKey foreignKey) {
  String table = foreignKey.getTable().getName();
  return spannerDatabaseInfo.getAllTables().contains(table)
      && spannerDatabaseInfo.getImportedForeignKeys(table).contains(foreignKey.getName());
}
 

@Override
public String[] getSqlCreateStrings(ForeignKey foreignKey, Metadata metadata) {
	if ( !dialect.hasAlterTable() ) {
		return NO_COMMANDS;
	}

	if ( !foreignKey.isCreationEnabled() ) {
		return NO_COMMANDS;
	}

	if ( !foreignKey.isPhysicalConstraint() ) {
		return NO_COMMANDS;
	}

	final int numberOfColumns = foreignKey.getColumnSpan();
	final String[] columnNames = new String[numberOfColumns];
	final String[] targetColumnNames = new String[numberOfColumns];

	final Iterator targetItr;
	if ( foreignKey.isReferenceToPrimaryKey() ) {
		if ( numberOfColumns != foreignKey.getReferencedTable().getPrimaryKey().getColumnSpan() ) {
			throw new AssertionFailure(
					String.format(
							Locale.ENGLISH,
							COLUMN_MISMATCH_MSG,
							numberOfColumns,
							foreignKey.getReferencedTable().getPrimaryKey().getColumnSpan(),
							foreignKey.getName(),
							foreignKey.getTable().getName(),
							foreignKey.getReferencedTable().getName()
					)
			);
		}
		targetItr = foreignKey.getReferencedTable().getPrimaryKey().getColumnIterator();
	}
	else {
		if ( numberOfColumns != foreignKey.getReferencedColumns().size() ) {
			throw new AssertionFailure(
					String.format(
							Locale.ENGLISH,
							COLUMN_MISMATCH_MSG,
							numberOfColumns,
							foreignKey.getReferencedColumns().size(),
							foreignKey.getName(),
							foreignKey.getTable().getName(),
							foreignKey.getReferencedTable().getName()
					)
			);
		}
		targetItr = foreignKey.getReferencedColumns().iterator();
	}

	int i = 0;
	final Iterator itr = foreignKey.getColumnIterator();
	while ( itr.hasNext() ) {
		columnNames[i] = ( (Column) itr.next() ).getQuotedName( dialect );
		targetColumnNames[i] = ( (Column) targetItr.next() ).getQuotedName( dialect );
		i++;
	}

	final JdbcEnvironment jdbcEnvironment = metadata.getDatabase().getJdbcEnvironment();
	final String sourceTableName = jdbcEnvironment.getQualifiedObjectNameFormatter().format(
			foreignKey.getTable().getQualifiedTableName(),
			dialect
	);
	final String targetTableName = jdbcEnvironment.getQualifiedObjectNameFormatter().format(
			foreignKey.getReferencedTable().getQualifiedTableName(),
			dialect
	);

	final StringBuilder buffer = new StringBuilder( dialect.getAlterTableString( sourceTableName ) )
			.append(
					foreignKey.getKeyDefinition() != null ?
							dialect.getAddForeignKeyConstraintString(
									foreignKey.getName(),
									foreignKey.getKeyDefinition()
							) :
							dialect.getAddForeignKeyConstraintString(
									foreignKey.getName(),
									columnNames,
									targetTableName,
									targetColumnNames,
									foreignKey.isReferenceToPrimaryKey()
							)
			);

	if ( dialect.supportsCascadeDelete() ) {
		if ( foreignKey.isCascadeDeleteEnabled() ) {
			buffer.append( " on delete cascade" );
		}
	}

	return new String[] { buffer.toString() };
}
 

public Exporter<ForeignKey> getForeignKeyExporter() {
	return foreignKeyExporter;
}
 

protected void secondPassCompileForeignKeys(
		final Table table,
		Set<ForeignKey> done,
		final MetadataBuildingContext buildingContext) throws MappingException {
	table.createForeignKeys();

	Iterator itr = table.getForeignKeyIterator();
	while ( itr.hasNext() ) {
		final ForeignKey fk = (ForeignKey) itr.next();
		if ( !done.contains( fk ) ) {
			done.add( fk );
			final String referencedEntityName = fk.getReferencedEntityName();
			if ( referencedEntityName == null ) {
				throw new MappingException(
						"An association from the table " +
								fk.getTable().getName() +
								" does not specify the referenced entity"
				);
			}

			log.debugf( "Resolving reference to class: %s", referencedEntityName );
			final PersistentClass referencedClass = getEntityBinding( referencedEntityName );
			if ( referencedClass == null ) {
				throw new MappingException(
						"An association from the table " +
								fk.getTable().getName() +
								" refers to an unmapped class: " +
								referencedEntityName
				);
			}
			if ( referencedClass.isJoinedSubclass() ) {
				secondPassCompileForeignKeys( referencedClass.getSuperclass().getTable(), done, buildingContext );
			}

			fk.setReferencedTable( referencedClass.getTable() );

			Identifier nameIdentifier;

			ImplicitForeignKeyNameSource foreignKeyNameSource = new ImplicitForeignKeyNameSource() {
				final List<Identifier> columnNames = extractColumnNames( fk.getColumns() );
				List<Identifier> referencedColumnNames = null;

				@Override
				public Identifier getTableName() {
					return table.getNameIdentifier();
				}

				@Override
				public List<Identifier> getColumnNames() {
					return columnNames;
				}

				@Override
				public Identifier getReferencedTableName() {
					return fk.getReferencedTable().getNameIdentifier();
				}

				@Override
				public List<Identifier> getReferencedColumnNames() {
					if ( referencedColumnNames == null ) {
						referencedColumnNames = extractColumnNames( fk.getReferencedColumns() );
					}
					return referencedColumnNames;
				}

				@Override
				public Identifier getUserProvidedIdentifier() {
					return fk.getName() != null ? Identifier.toIdentifier( fk.getName() ) : null;
				}

				@Override
				public MetadataBuildingContext getBuildingContext() {
					return buildingContext;
				}
			};

			nameIdentifier = getMetadataBuildingOptions().getImplicitNamingStrategy().determineForeignKeyName(foreignKeyNameSource);

			fk.setName( nameIdentifier.render( getDatabase().getJdbcEnvironment().getDialect() ) );

			fk.alignColumns();
		}
	}
}
 

@Override
public Exporter<ForeignKey> getForeignKeyExporter() {
    return getInstance().getForeignKeyExporter();
}