# ElementRecordMapping.java

    package org.codefilarete.stalactite.engine.configurer.elementcollection;

    import java.util.Collections;
    import java.util.HashMap;
    import java.util.Map;
    import java.util.function.Function;

    import org.codefilarete.reflection.ReadWriteAccessPoint;
    import org.codefilarete.stalactite.mapping.ComposedIdMapping;
    import org.codefilarete.stalactite.mapping.DefaultEntityMapping;
    import org.codefilarete.stalactite.mapping.EmbeddedClassMapping;
    import org.codefilarete.stalactite.mapping.IdAccessor;
    import org.codefilarete.stalactite.mapping.IdMapping;
    import org.codefilarete.stalactite.mapping.id.assembly.ComposedIdentifierAssembler;
    import org.codefilarete.stalactite.mapping.id.assembly.IdentifierAssembler;
    import org.codefilarete.stalactite.mapping.id.manager.AlreadyAssignedIdentifierManager;
    import org.codefilarete.stalactite.query.api.Selectable;
    import org.codefilarete.stalactite.sql.ddl.structure.Column;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.stalactite.sql.result.ColumnedRow;
    import org.codefilarete.tool.VisibleForTesting;
    import org.codefilarete.tool.collection.Maps;

    /**
     * Class mapping dedicated to {@link ElementRecord}. Very close to {@link org.codefilarete.stalactite.engine.configurer.AssociationRecordMapping}
     * in its principle.
     */
    public class ElementRecordMapping<C, I, T extends Table<T>, ER extends ElementRecord<C, I>> extends DefaultEntityMapping<ER, ER, T> {

    	@VisibleForTesting
    	public <LEFTTABLE extends Table<LEFTTABLE>> ElementRecordMapping(T targetTable,
    	                                                                 Column<T, C> elementColumn,
    	                                                                 IdentifierAssembler<I, LEFTTABLE> sourceIdentifierAssembler,
    	                                                                 Map<Column<LEFTTABLE, ?>, Column<T, ?>> foreignKeyColumnMapping) {
    		super((Class) ElementRecord.class,
    				targetTable,
    				(Map) Maps.forHashMap(ReadWriteAccessPoint.class, Column.class)
    						.add(ElementRecord.ELEMENT_ACCESSOR, elementColumn),
    				new ElementRecordIdMapping<>(targetTable, elementColumn, sourceIdentifierAssembler, foreignKeyColumnMapping));
    	}

    	public <LEFTTABLE extends Table<LEFTTABLE>> ElementRecordMapping(T targetTable,
    	                                                                 EmbeddedClassMapping<ER, T> embeddableMapping,
    	                                                                 IdentifierAssembler<I, LEFTTABLE> sourceIdentifierAssembler,
    	                                                                 Map<Column<LEFTTABLE, ?>, Column<T, ?>> foreignKeyColumnMapping) {
    		super((Class) ElementRecord.class,
    				targetTable,
    				embeddableMapping.getPropertyToColumn(),
    				Collections.emptyMap(),
    				null,
    				new ElementRecordIdMapping<>(targetTable, embeddableMapping, sourceIdentifierAssembler, foreignKeyColumnMapping),
    				new Function<ColumnedRow, ER>() {
    					@Override
    					public ER apply(ColumnedRow columnedRow) {
    						I id = sourceIdentifierAssembler.assemble(columnedRow);
    						return (ER) new ElementRecord<>(id, null);
    					}
    				},
    				true);
    	}

    	/**
    	 * {@link IdMapping} for {@link ElementRecord} : a composed id made of :
    	 * - {@link ElementRecord#getId()}
    	 * - {@link ElementRecord#getElement()}
    	 */
    	public static class ElementRecordIdMapping<C, I, T extends Table<T>, ER extends ElementRecord<C, I>> extends ComposedIdMapping<ER, ER> {

    		public <LEFTTABLE extends Table<LEFTTABLE>> ElementRecordIdMapping(
    				T targetTable,
    				Column<T, C> elementColumn,
    				IdentifierAssembler<I, LEFTTABLE> sourceIdentifierAssembler,
    				Map<Column<LEFTTABLE, ?>, Column<T, ?>> foreignKeyColumnMapping) {
    			super(new ElementRecordIdMapping.ElementRecordIdAccessor<>(),
    					new AlreadyAssignedIdentifierManager<>((Class<ER>) (Class) ElementRecord.class,
    							ElementRecord::markAsPersisted,
    							ElementRecord::isPersisted),
    					new ElementRecordIdMapping.DefaultElementRecordIdentifierAssembler<>(targetTable, elementColumn, sourceIdentifierAssembler, foreignKeyColumnMapping));
    		}

    		public <LEFTTABLE extends Table<LEFTTABLE>> ElementRecordIdMapping(
    				T targetTable,
    				EmbeddedClassMapping<ER, T> elementMapping,
    				IdentifierAssembler<I, LEFTTABLE> sourceIdentifierAssembler,
    				Map<Column<LEFTTABLE, ?>, Column<T, ?>> primaryKeyForeignColumnMapping) {
    			super(new ElementRecordIdMapping.ElementRecordIdAccessor<>(),
    					new AlreadyAssignedIdentifierManager<>((Class<ER>) (Class) ElementRecord.class,
    							ElementRecord::markAsPersisted,
    							ElementRecord::isPersisted),
    					new ElementRecordIdentifierAssembler<>(targetTable, elementMapping, sourceIdentifierAssembler, primaryKeyForeignColumnMapping));
    		}

    		/**
    		 * Override because {@link ComposedIdMapping} is based on null identifier to determine newness, which is always false for {@link ElementRecord}
    		 * because they always have one. We delegate its computation to the entity.
    		 *
    		 * @param entity any non-null entity
    		 * @return true or false based on {@link ElementRecord#isNew()}
    		 */
    		@Override
    		public boolean isNew(ER entity) {
    			return entity.isNew();
    		}

    		private static class ElementRecordIdAccessor<C, I, ER extends ElementRecord<C, I>> implements IdAccessor<ER, ER> {

    			@Override
    			public ER getId(ER associationRecord) {
    				return associationRecord;
    			}

    			@Override
    			public void setId(ER associationRecord, ER identifier) {
    				associationRecord.setId(identifier.getId());
    				associationRecord.setElement(identifier.getElement());
    			}
    		}

    		/**
    		 * Identifier assembler when {@link ElementRecord} is persisted according to a default behavior :
    		 * - identifier is saved in table primary key
    		 * - element value is saved in elementColumn
    		 *
    		 * @param <TRGT> embedded bean type
    		 * @param <ID>   source identifier type
    		 */
    		public static class DefaultElementRecordIdentifierAssembler<TRGT, ID, T extends Table<T>, ER extends ElementRecord<TRGT, ID>> extends ComposedIdentifierAssembler<ER, T> {

    			private final Column<T, TRGT> elementColumn;
    			private final IdentifierAssembler<ID, ?> sourceIdentifierAssembler;
    			private final Map<Column<?, ?>, Column<T, ?>> foreignKeyColumnMapping;

    			private <LEFTTABLE extends Table<LEFTTABLE>> DefaultElementRecordIdentifierAssembler(T targetTable,
    			                                                                                     Column<T, TRGT> elementColumn,
    			                                                                                     IdentifierAssembler<ID, LEFTTABLE> sourceIdentifierAssembler,
    			                                                                                     Map<Column<LEFTTABLE, ?>, Column<T, ?>> foreignKeyColumnMapping) {
    				super(targetTable);
    				this.elementColumn = elementColumn;
    				this.sourceIdentifierAssembler = sourceIdentifierAssembler;
    				this.foreignKeyColumnMapping = (Map) foreignKeyColumnMapping;
    			}

    			public Column<T, TRGT> getElementColumn() {
    				return elementColumn;
    			}

    			public IdentifierAssembler<ID, ?> getSourceIdentifierAssembler() {
    				return sourceIdentifierAssembler;
    			}

    			@Override
    			public ER assemble(ColumnedRow columnValueProvider) {
    				ID leftValue = sourceIdentifierAssembler.assemble(new ColumnedRow() {
    					@Override
    					public <E> E get(Selectable<E> sourceColumn) {
    						Column<T, E> targetColumn = (Column<T, E>) foreignKeyColumnMapping.get(sourceColumn);
    						return columnValueProvider.get(targetColumn);
    					}
    				});
    				TRGT rightValue = columnValueProvider.get(elementColumn);
    				// we should not return an id if any (both expected in fact) value is null
    				if (leftValue == null || rightValue == null) {
    					return null;
    				} else {
    					return (ER) new ElementRecord<>(leftValue, rightValue);
    				}
    			}

    			@Override
    			public Map<Column<T, ?>, Object> getColumnValues(ER id) {
    				Map<Column<?, ?>, Object> sourceColumnValues = (Map) sourceIdentifierAssembler.getColumnValues(id.getId());
    				Map<Column<T, ?>, Object> idColumnValues = Maps.innerJoin(foreignKeyColumnMapping, sourceColumnValues);
    				Map<Column<T, ?>, Object> result = new HashMap<>();
    				result.put(elementColumn, id.getElement());
    				result.putAll(idColumnValues);
    				return result;
    			}
    		}

    		/**
    		 * Identifier assembler for cases where user gave a configuration to persist embedded beans (default way is not used)
    		 *
    		 * @param <TRGT> embedded bean type
    		 * @param <ID>   source identifier type
    		 */
    		public static class ElementRecordIdentifierAssembler<TRGT, ID, T extends Table<T>, ER extends ElementRecord<TRGT, ID>> extends ComposedIdentifierAssembler<ER, T> {

    			private final EmbeddedClassMapping<ER, T> elementMapping;
    			private final IdentifierAssembler<ID, ?> sourceIdentifierAssembler;
    			private final Map<Column<?, ?>, Column<T, ?>> foreignKeyColumnMapping;

    			private <LEFTTABLE extends Table<LEFTTABLE>> ElementRecordIdentifierAssembler(
    					T targetTable,
    					EmbeddedClassMapping<ER, T> elementMapping,
    					IdentifierAssembler<ID, LEFTTABLE> sourceIdentifierAssembler,
    					Map<Column<LEFTTABLE, ?>, Column<T, ?>> foreignKeyColumnMapping) {
    				super(targetTable);
    				this.elementMapping = elementMapping;
    				this.sourceIdentifierAssembler = sourceIdentifierAssembler;
    				this.foreignKeyColumnMapping = (Map) foreignKeyColumnMapping;
    			}

    			public EmbeddedClassMapping<ER, T> getElementMapping() {
    				return elementMapping;
    			}

    			@Override
    			public ER assemble(ColumnedRow row) {
    				return elementMapping.transform(row);
    			}

    			@Override
    			public Map<Column<T, ?>, Object> getColumnValues(ER id) {
    				Map<Column<?, ?>, Object> sourceColumnValues = (Map) sourceIdentifierAssembler.getColumnValues(id.getId());
    				Map<Column<T, ?>, Object> idColumnValues = Maps.innerJoin(foreignKeyColumnMapping, sourceColumnValues);
    				Map<Column<T, ?>, Object> result = new HashMap<>();
    				result.putAll(idColumnValues);
    				result.putAll(elementMapping.getInsertValues(id));
    				return result;
    			}
    		}
    	}
    }