code: public ExtendedRelation addRelationship(String baseTableName,
  			String relatedTableName, String mappingTableName,
  			String relationName) {
  
  		UserMappingTable userMappingTable = UserMappingTable
  				.create(mappingTableName);
  
  		ExtendedRelation extendedRelation = addRelationship(baseTableName,
  				relatedTableName, userMappingTable, relationName);
  
  		return extendedRelation;
  	}
docs: Adds a relationship between the base and related table. Creates a default
  user mapping table if needed.
  
  @param baseTableName
  base table name
  @param relatedTableName
  related table name
  @param mappingTableName
  mapping table name
  @param relationName
  relation name
  @return The relationship that was added