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 *  or more contributor license agreements.  See the NOTICE file
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 *  to you under the Apache License, Version 2.0 (the
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package org.apache.cayenne.util;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.cayenne.PersistenceState;
import org.apache.cayenne.Persistent;
import org.apache.cayenne.map.EntityResolver;
import org.apache.cayenne.map.ObjEntity;
import org.apache.cayenne.map.ObjRelationship;
import org.apache.cayenne.property.Property;
import org.apache.cayenne.query.RelationshipQuery;

/**
 * An abstract superlcass of lazily faulted to-one and to-many relationships.
 * 
 * @since 1.2
 * @author Andrus Adamchik
 */
public abstract class RelationshipFault {

    protected Persistent relationshipOwner;
    protected String relationshipName;

    protected RelationshipFault() {

    }

    public RelationshipFault(Persistent relationshipOwner, String relationshipName) {
        if (relationshipOwner == null) {
            throw new NullPointerException("'relationshipOwner' can't be null.");
        }

        if (relationshipName == null) {
            throw new NullPointerException("'relationshipName' can't be null.");
        }

        this.relationshipOwner = relationshipOwner;
        this.relationshipName = relationshipName;
    }

    public String getRelationshipName() {
        return relationshipName;
    }

    public Persistent getRelationshipOwner() {
        return relationshipOwner;
    }

    protected boolean isTransientParent() {
        int state = relationshipOwner.getPersistenceState();
        return state == PersistenceState.NEW || state == PersistenceState.TRANSIENT;
    }

    protected boolean isUncommittedParent() {
        int state = relationshipOwner.getPersistenceState();
        return state == PersistenceState.MODIFIED || state == PersistenceState.DELETED;
    }

    /**
     * Executes a query that returns related objects. Subclasses would invoke this method
     * whenever they need to resolve a fault.
     */
    protected List resolveFromDB() {
        // non-persistent objects shouldn't trigger a fetch
        if (isTransientParent()) {
            return new ArrayList();
        }

        List resolved = relationshipOwner.getObjectContext().performQuery(
                new RelationshipQuery(
                        relationshipOwner.getObjectId(),
                        relationshipName,
                        false));

        if (resolved.isEmpty()) {
            return resolved;
        }

        // see if reverse relationship is to-one and we can connect source to results....

        EntityResolver resolver = relationshipOwner
                .getObjectContext()
                .getEntityResolver();
        ObjEntity sourceEntity = resolver.lookupObjEntity(relationshipOwner
                .getObjectId()
                .getEntityName());

        ObjRelationship relationship = (ObjRelationship) sourceEntity
                .getRelationship(relationshipName);
        ObjRelationship reverse = relationship.getReverseRelationship();

        if (reverse != null && !reverse.isToMany()) {
            Property property = resolver
                    .getClassDescriptor(reverse.getSourceEntity().getName())
                    .getProperty(reverse.getName());

            Iterator it = resolved.iterator();
            while (it.hasNext()) {
                property.writePropertyDirectly(it.next(), null, relationshipOwner);
            }
        }

        return resolved;
    }
}