# SingleTablePolymorphismEntityFinder.java

    package org.codefilarete.stalactite.engine.runtime.singletable;

    import java.sql.ResultSet;
    import java.util.Collection;
    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Map;
    import java.util.Set;
    import java.util.stream.Collectors;

    import org.codefilarete.stalactite.dsl.PolymorphismPolicy.SingleTablePolymorphism;
    import org.codefilarete.stalactite.engine.configurer.builder.PersisterBuilderContext;
    import org.codefilarete.stalactite.engine.configurer.builder.BuildLifeCycleListener;
    import org.codefilarete.stalactite.engine.runtime.AbstractPolymorphicEntityFinder;
    import org.codefilarete.stalactite.engine.runtime.ConfiguredRelationalPersister;
    import org.codefilarete.stalactite.engine.runtime.load.EntityJoinTree;
    import org.codefilarete.stalactite.engine.runtime.load.EntityTreeQueryBuilder;
    import org.codefilarete.stalactite.engine.runtime.load.EntityTreeQueryBuilder.EntityTreeQuery;
    import org.codefilarete.stalactite.engine.runtime.load.JoinTableRootJoinNode;
    import org.codefilarete.stalactite.engine.runtime.load.SingleTableRootJoinNode;
    import org.codefilarete.stalactite.engine.runtime.query.EntityCriteriaSupport;
    import org.codefilarete.stalactite.engine.runtime.query.EntityQueryCriteriaSupport;
    import org.codefilarete.stalactite.mapping.id.assembly.IdentifierAssembler;
    import org.codefilarete.stalactite.query.ConfiguredEntityCriteria;
    import org.codefilarete.stalactite.query.builder.QuerySQLBuilderFactory.QuerySQLBuilder;
    import org.codefilarete.stalactite.query.model.GroupBy;
    import org.codefilarete.stalactite.query.model.Having;
    import org.codefilarete.stalactite.query.model.Limit;
    import org.codefilarete.stalactite.query.model.OrderBy;
    import org.codefilarete.stalactite.query.model.Query;
    import org.codefilarete.stalactite.query.model.Select;
    import org.codefilarete.stalactite.query.model.Selectable;
    import org.codefilarete.stalactite.query.model.Where;
    import org.codefilarete.stalactite.sql.ConnectionProvider;
    import org.codefilarete.stalactite.sql.Dialect;
    import org.codefilarete.stalactite.sql.ddl.structure.Column;
    import org.codefilarete.stalactite.sql.ddl.structure.PrimaryKey;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.stalactite.sql.result.ColumnedRowIterator;
    import org.codefilarete.stalactite.sql.statement.PreparedSQL;
    import org.codefilarete.stalactite.sql.statement.ReadOperation;
    import org.codefilarete.stalactite.sql.statement.SQLExecutionException;
    import org.codefilarete.stalactite.sql.statement.binder.ResultSetReader;
    import org.codefilarete.tool.VisibleForTesting;
    import org.codefilarete.tool.collection.KeepOrderMap;
    import org.codefilarete.tool.collection.KeepOrderSet;

    import static org.codefilarete.stalactite.engine.runtime.load.EntityJoinTree.ROOT_JOIN_NAME;

    /**
     * @author Guillaume Mary
     */
    public class SingleTablePolymorphismEntityFinder<C, I, T extends Table<T>, DTYPE> extends AbstractPolymorphicEntityFinder<C, I, T> {

    	@VisibleForTesting
    	static final String DISCRIMINATOR_ALIAS = "DISCRIMINATOR";

    	private final IdentifierAssembler<I, T> identifierAssembler;
    	private final Column<T, DTYPE> discriminatorColumn;
    	private final SingleTablePolymorphism<C, DTYPE> polymorphismPolicy;
    	private final EntityJoinTree<C, I> singleLoadEntityJoinTree;
    	private final EntityCriteriaSupport<C> criteriaSupport;
    	private Query query;
    	private EntityTreeQuery<C> entityTreeQuery;

    	public SingleTablePolymorphismEntityFinder(ConfiguredRelationalPersister<C, I> mainPersister,
    											   Map<? extends Class<C>, ? extends ConfiguredRelationalPersister<C, I>> persisterPerSubclass,
    											   Column<T, DTYPE> discriminatorColumn,
    											   SingleTablePolymorphism<C, DTYPE> polymorphismPolicy,
    											   ConnectionProvider connectionProvider,
    											   Dialect dialect) {
    		super(mainPersister, persisterPerSubclass, connectionProvider, dialect);
    		this.identifierAssembler = mainPersister.getMapping().getIdMapping().getIdentifierAssembler();
    		this.discriminatorColumn = discriminatorColumn;
    		this.polymorphismPolicy = polymorphismPolicy;
    		this.singleLoadEntityJoinTree = buildSingleLoadEntityJoinTree(mainPersister, persisterPerSubclass);
    		this.criteriaSupport = new EntityCriteriaSupport<>(singleLoadEntityJoinTree);

    		// made for optimization (to avoid creating multiple times the query) but also to avoid adding several times the polymorphic JoinNode consumers
    		// to itself by calling several time the "toConsumer(..)" method that usually calls some "add" method, which declares duplicates of consumers,
    		// which, at the very end, implies an exception during the aggregate inflation phase : "Can't find consumer node"
    		PersisterBuilderContext.CURRENT.get().addBuildLifeCycleListener(new BuildLifeCycleListener() {
    			@Override
    			public void afterBuild() {
    			}

    			@Override
    			public void afterAllBuild() {
    				buildQuery();
    			}
    		});
    	}

    	private void buildQuery() {
    		entityTreeQuery = new EntityTreeQueryBuilder<>(singleLoadEntityJoinTree, dialect.getColumnBinderRegistry()).buildSelectQuery();
    		query = entityTreeQuery.getQuery();
    	}

    	@Override
    	protected EntityTreeQuery<C> getAggregateQueryTemplate() {
    		return entityTreeQuery;
    	}

    	@Override
    	public EntityJoinTree<C, I> getEntityJoinTree() {
    		return singleLoadEntityJoinTree;
    	}

    	@Override
    	public EntityQueryCriteriaSupport<C, I> newCriteriaSupport() {
    		return new EntityQueryCriteriaSupport<>(this, criteriaSupport.copy());
    	}

    	private SingleLoadEntityJoinTree<C, I, DTYPE> buildSingleLoadEntityJoinTree(ConfiguredRelationalPersister<C, I> mainPersister, Map<? extends Class<C>, ? extends ConfiguredRelationalPersister<C, I>> persisterPerSubclass) {
    		SingleLoadEntityJoinTree<C, I, DTYPE> result = new SingleLoadEntityJoinTree<>(
    				mainPersister,
    				new HashSet<>(persisterPerSubclass.values()),
    				discriminatorColumn,
    				polymorphismPolicy
    		);
    		// we project main persister tree to keep its relations
    		mainPersister.getEntityJoinTree().projectTo(result, ROOT_JOIN_NAME);
    		// we add the joins of the sub-persister to the whole graph to make it load its relations
    		persisterPerSubclass.values().forEach(subPersister -> {
    			subPersister.getEntityJoinTree().projectTo(result, ROOT_JOIN_NAME);
    		});
    		return result;
    	}

    	@Override
    	public Set<C> selectWithSingleQuery(ConfiguredEntityCriteria where, Map<String, Object> values, OrderBy orderBy, Limit limit) {
    		LOGGER.debug("Finding entities in a single query with criteria {}", where);
    		if (hasSubPolymorphicPersister) {
    			LOGGER.debug("Single query was asked but due to sub-polymorphism the query is made in 2 phases");
    			return selectIn2Phases(where, values, orderBy, limit);
    		} else {
    			Where add = new Where<>();
    			add.add(query.getWhereDelegate().getConditions());
    			add.add(where.getCriteria());
    			Query queryClone = new Query(query.getSelectDelegate(), query.getFromDelegate(), add, new GroupBy(), new Having(), orderBy, limit);
    			return super.selectWithSingleQuery(queryClone, values, entityTreeQuery, dialect, connectionProvider);
    		}
    	}

    	@Override
    	public Set<C> selectIn2Phases(ConfiguredEntityCriteria where, Map<String, Object> values, OrderBy orderBy, Limit limit) {
    		LOGGER.debug("Finding entities in 2-phases query with criteria {}", where);

    		// we clone the query to avoid polluting the instance one, else, from select(..) to select(..), we append the criteria at the end of it,
    		// which makes the query usually returning no data (because of the condition mix)
    		Query queryClone = new Query(new Select(), query.getFromDelegate(), new Where<>(where.getCriteria()), new GroupBy(), new Having(), orderBy, limit);

    		QuerySQLBuilder sqlQueryBuilder = dialect.getQuerySQLBuilderFactory().queryBuilder(queryClone);

    		// First phase : selecting ids (made by clearing selected elements for performance issue)
    		PrimaryKey<T, I> pk = ((T) mainEntityJoinTree.getRoot().getTable()).getPrimaryKey();
    		pk.getColumns().forEach(column -> queryClone.select(column, column.getAlias()));
    		queryClone.select(discriminatorColumn, DISCRIMINATOR_ALIAS);

    		// selecting ids and their entity type
    		Map<Selectable<?>, ResultSetReader<?>> columnReaders = new HashMap<>();
    		queryClone.getColumns().forEach(selectable -> columnReaders.put(selectable, dialect.getColumnBinderRegistry().getBinder((Column) selectable)));

    		Map<Class, Set<I>> idsPerSubtype = readIds(sqlQueryBuilder.toPreparableSQL().toPreparedSQL(values), columnReaders, queryClone.getAliases());

    		// Second phase : selecting entities by delegating it to each subclass loader
    		// It will generate 1 query per found subclass, made as this :
    		// - to avoid superfluous join and complex query in case of relation
    		// - make it simpler to implement
    		Set<I> ids = idsPerSubtype.values().stream().flatMap(Collection::stream).collect(Collectors.toSet());

    		if (hasSubPolymorphicPersister) {
    			LOGGER.debug("Asking sub-polymorphic persisters to load the entities");
    			Set<C> result = new HashSet<>();
    			idsPerSubtype.forEach((k, v) -> result.addAll(persisterPerSubclass.get(k).select(v)));
    			return result;
    		} else {
    			return selectWithSingleQueryWhereIdIn(ids);
    		}
    	}

    	private Map<Class, Set<I>> readIds(PreparedSQL preparedSQL, Map<Selectable<?>, ResultSetReader<?>> columnReaders, Map<Selectable<?>, String> aliases) {
    		try (ReadOperation<Integer> closeableOperation = dialect.getReadOperationFactory().createInstance(preparedSQL, connectionProvider)) {
    			ResultSet resultSet = closeableOperation.execute();
    			ColumnedRowIterator rowIterator = new ColumnedRowIterator(resultSet, columnReaders, aliases);
    			// Below we keep the order of given entities mainly to get steady unit tests. Meanwhile, this may have performance
    			// impacts but it's very difficult to measure
    			Map<Class, Set<I>> result = new KeepOrderMap<>();
    			rowIterator.forEachRemaining(row -> {
    				DTYPE dtype = (DTYPE) row.get(discriminatorColumn);
    				I id = identifierAssembler.assemble(row);
    				result.computeIfAbsent(polymorphismPolicy.getClass(dtype), k -> new KeepOrderSet<>()).add(id);
    			});
    			return result;
    		} catch (RuntimeException e) {
    			throw new SQLExecutionException(preparedSQL.getSQL(), e);
    		}
    	}

    	/**
    	 * Appropriate {@link EntityJoinTree} to instantiate {@link JoinTableRootJoinNode} as root in order to handle join-node polymorphism of root entity.
    	 * @param <C>
    	 * @param <I>
    	 * @author Guillaume Mary
    	 */
    	private static class SingleLoadEntityJoinTree<C, I, DTYPE> extends EntityJoinTree<C, I> {

    		public <T extends Table<T>> SingleLoadEntityJoinTree(ConfiguredRelationalPersister<C, I> mainPersister,
    															 Set<? extends ConfiguredRelationalPersister<C, I>> subPersisters,
    															 Column<T, DTYPE> discriminatorColumn,
    															 SingleTablePolymorphism<C, DTYPE> polymorphismPolicy) {
    			super(self -> new SingleTableRootJoinNode<>(
    					self,
    					mainPersister,
    					subPersisters,
    					discriminatorColumn,
    					polymorphismPolicy)
    			);
    		}
    	}
    }