# ManyToOneRelation.java

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

    import java.lang.reflect.Method;
    import java.util.Collection;
    import java.util.function.BooleanSupplier;
    import java.util.function.Supplier;

    import org.codefilarete.reflection.Accessor;
    import org.codefilarete.reflection.AccessorByMethod;
    import org.codefilarete.reflection.AccessorByMethodReference;
    import org.codefilarete.reflection.AccessorChain;
    import org.codefilarete.reflection.Accessors;
    import org.codefilarete.reflection.MethodReferenceCapturer;
    import org.codefilarete.reflection.MutatorByMethod;
    import org.codefilarete.reflection.MutatorByMethodReference;
    import org.codefilarete.reflection.PropertyAccessor;
    import org.codefilarete.reflection.ReversibleAccessor;
    import org.codefilarete.stalactite.dsl.PolymorphismPolicy;
    import org.codefilarete.stalactite.dsl.entity.EntityMappingConfiguration;
    import org.codefilarete.stalactite.dsl.entity.EntityMappingConfigurationProvider;
    import org.codefilarete.stalactite.dsl.property.CascadeOptions.RelationMode;
    import org.codefilarete.tool.Nullable;
    import org.danekja.java.util.function.serializable.SerializableBiConsumer;
    import org.danekja.java.util.function.serializable.SerializableFunction;

    import static org.codefilarete.tool.Nullable.nullable;

    /**
     * @author Guillaume Mary
     */
    public class ManyToOneRelation<SRC, TRGT, TRGTID, C extends Collection<SRC>> {

    	/** The method that gives the target entity from the source one */
    	private final ReversibleAccessor<SRC, TRGT> targetProvider;

    	/** Configuration used for target beans persistence */
    	private final EntityMappingConfigurationProvider<TRGT, TRGTID> targetMappingConfiguration;

    	private final BooleanSupplier sourceTablePerClassPolymorphic;

    	private boolean nullable = true;

    	/** Default relation mode is {@link RelationMode#ALL} */
    	private RelationMode relationMode = RelationMode.ALL;

    	private final MappedByConfiguration<SRC, TRGT, C> mappedByConfiguration = new MappedByConfiguration<>();

    	/**
    	 * Indicates that relation must be loaded in same main query (through join) or in some separate query
    	 */
    	private boolean fetchSeparately;

    	@javax.annotation.Nullable
    	private String columnName;

    	/**
    	 *
    	 * @param targetProvider provider of the property to be persisted
    	 * @param sourceTablePerClassPolymorphic indicates that source is table-per-class polymorphic
    	 * @param targetMappingConfiguration persistence configuration provider of entities stored in the target collection
    	 */
    	public ManyToOneRelation(ReversibleAccessor<SRC, TRGT> targetProvider,
    							 BooleanSupplier sourceTablePerClassPolymorphic,
    							 EntityMappingConfigurationProvider<? extends TRGT, TRGTID> targetMappingConfiguration) {
    		this.sourceTablePerClassPolymorphic = sourceTablePerClassPolymorphic;
    		this.targetMappingConfiguration = (EntityMappingConfigurationProvider<TRGT, TRGTID>) targetMappingConfiguration;
    		this.targetProvider = targetProvider;
    	}

    	/** Original method reference given for mapping */
    	public ReversibleAccessor<SRC, TRGT> getTargetProvider() {
    		return targetProvider;
    	}

    	public boolean isSourceTablePerClassPolymorphic() {
    		return sourceTablePerClassPolymorphic.getAsBoolean();
    	}

    	/** @return the configuration used for target beans persistence */
    	public EntityMappingConfiguration<TRGT, TRGTID> getTargetMappingConfiguration() {
    		return targetMappingConfiguration.getConfiguration();
    	}

    	public boolean isTargetTablePerClassPolymorphic() {
    		return getTargetMappingConfiguration().getPolymorphismPolicy() instanceof PolymorphismPolicy.TablePerClassPolymorphism;
    	}

    	/** Nullable option, mainly for column join and DDL schema generation */
    	public boolean isNullable() {
    		return nullable;
    	}

    	public void setNullable(boolean nullable) {
    		this.nullable = nullable;
    	}

    	public RelationMode getRelationMode() {
    		return relationMode;
    	}

    	public void setRelationMode(RelationMode relationMode) {
    		this.relationMode = relationMode;
    	}

    	public MappedByConfiguration<SRC, TRGT, C> getMappedByConfiguration() {
    		return mappedByConfiguration;
    	}

    	public boolean isFetchSeparately() {
    		return fetchSeparately;
    	}

    	public void setFetchSeparately(boolean fetchSeparately) {
    		this.fetchSeparately = fetchSeparately;
    	}

    	public void fetchSeparately() {
    		setFetchSeparately(true);
    	}

    	@javax.annotation.Nullable
    	public String getColumnName() {
    		return columnName;
    	}

    	public void setColumnName(@javax.annotation.Nullable String columnName) {
    		this.columnName = columnName;
    	}

    	/**
    	 * Build the accessor for the reverse property, made of configured getter and setter. If one of them is unavailable, it's deduced from the
    	 * present one. If both are absent, null is returned.
    	 *
    	 * @return null if no getter nor setter were defined
    	 */
    	@javax.annotation.Nullable
    	PropertyAccessor<TRGT, C> buildReversePropertyAccessor() {
    		Nullable<AccessorByMethodReference<TRGT, C>> getterReference = nullable(mappedByConfiguration.getAccessor()).map(Accessors::accessorByMethodReference);
    		Nullable<MutatorByMethodReference<TRGT, C>> setterReference = nullable(mappedByConfiguration.getMutator()).map(Accessors::mutatorByMethodReference);
    		if (getterReference.isAbsent() && setterReference.isAbsent()) {
    			return null;
    		} else if (getterReference.isPresent() && setterReference.isPresent()) {
    			// we keep close to user demand : we keep its method references
    			return new PropertyAccessor<>(getterReference.get(), setterReference.get());
    		} else if (getterReference.isPresent() && setterReference.isAbsent()) {
    			// we keep close to user demand : we keep its method reference ...
    			// ... but we can't do it for mutator, so we use the most equivalent manner : a mutator based on setter method (fallback to property if not present)
    			return new PropertyAccessor<>(getterReference.get(), new AccessorByMethod<TRGT, C>(captureMethod(mappedByConfiguration.getAccessor())).toMutator());
    		} else {
    			// we keep close to user demand : we keep its method reference ...
    			// ... but we can't do it for getter, so we use the most equivalent manner : a mutator based on setter method (fallback to property if not present)
    			return new PropertyAccessor<>(new MutatorByMethod<TRGT, C>(captureMethod(mappedByConfiguration.getMutator())).toAccessor(), setterReference.get());
    		}
    	}

    	private final MethodReferenceCapturer methodSpy = new MethodReferenceCapturer();

    	private Method captureMethod(SerializableFunction getter) {
    		return this.methodSpy.findMethod(getter);
    	}

    	private Method captureMethod(SerializableBiConsumer setter) {
    		return this.methodSpy.findMethod(setter);
    	}

    	/**
    	 * Clones this object to create a new one with the given accessor as prefix of current one.
    	 * Made to shift the current instance with an accessor prefix. Used for embeddable objects with relation to make the relation being accessible
    	 * from the "root" entity.
    	 *
    	 * @param accessor the prefix of the clone to be created
    	 * @return a clone of this instance prefixed with the given accessor
    	 * @param <E> the root entity type that owns the embeddable which has this relation
    	 */
    	public <E, CC extends Collection<E>> ManyToOneRelation<E, TRGT, TRGTID, CC> embedInto(Accessor<E, SRC> accessor) {
    		AccessorChain<E, TRGT> shiftedTargetProvider = new AccessorChain<>(accessor, targetProvider);
    		ManyToOneRelation<E, TRGT, TRGTID, CC> result = new ManyToOneRelation<>(shiftedTargetProvider, this::isSourceTablePerClassPolymorphic, this::getTargetMappingConfiguration);
    		result.setRelationMode(this.getRelationMode());
    		result.setNullable(this.isNullable());
    		result.setFetchSeparately(this.isFetchSeparately());
    		result.setColumnName(this.getColumnName());
    		return result;
    	}

    	public static class MappedByConfiguration<SRC, TRGT, C2 extends Collection<SRC>> {

    		/**
    		 * Combiner of target entity with source entity
    		 */
    		@javax.annotation.Nullable
    		private SerializableBiConsumer<TRGT, SRC> combiner;

    		/**
    		 * Source getter on target for bidirectionality (no consequence on database mapping).
    		 */
    		@javax.annotation.Nullable
    		private SerializableFunction<TRGT, C2> accessor;

    		/**
    		 * Source setter on target for bidirectionality (no consequence on database mapping).
    		 */
    		@javax.annotation.Nullable
    		private SerializableBiConsumer<TRGT, C2> mutator;

    		/** Optional provider of collection instance to be used if collection value is null */
    		@javax.annotation.Nullable
    		private Supplier<C2> factory;

    		@javax.annotation.Nullable
    		public SerializableBiConsumer<TRGT, SRC> getCombiner() {
    			return combiner;
    		}

    		public void setCombiner(@javax.annotation.Nullable SerializableBiConsumer<TRGT, SRC> combiner) {
    			this.combiner = combiner;
    		}

    		@javax.annotation.Nullable
    		public SerializableFunction<TRGT, C2> getAccessor() {
    			return accessor;
    		}

    		public void setAccessor(@javax.annotation.Nullable SerializableFunction<TRGT, C2> accessor) {
    			this.accessor = accessor;
    		}

    		@javax.annotation.Nullable
    		public SerializableBiConsumer<TRGT, C2> getMutator() {
    			return mutator;
    		}

    		public void setMutator(@javax.annotation.Nullable SerializableBiConsumer<TRGT, C2> mutator) {
    			this.mutator = mutator;
    		}

    		@javax.annotation.Nullable
    		public Supplier<C2> getFactory() {
    			return factory;
    		}

    		public void setFactory(@javax.annotation.Nullable Supplier<C2> factory) {
    			this.factory = factory;
    		}

    		public boolean isEmpty() {
    			return accessor == null && mutator == null && factory == null && combiner == null;
    		}
    	}
    }