Relationship.java

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package org.apache.cayenne.map;

import java.io.Serializable;

import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.util.CayenneMapEntry;
import org.apache.cayenne.util.ToStringBuilder;
import org.apache.cayenne.util.XMLSerializable;

/**
 * Defines a relationship between two entities. In a DataMap graph relationships represent
 * "arcs" connecting entity "nodes". Relationships are directional, i.e. they have a
 * notion of source and target entity. This makes DataMap a "digraph".
 */
public abstract class Relationship implements CayenneMapEntry, XMLSerializable,
        Serializable {

    protected String name;
    protected Entity sourceEntity;

    protected String targetEntityName;
    protected boolean toMany;

    /**
     * A flag that specifies whether a Relationship was mapped by the user or added
     * dynamically by Cayenne runtime.
     * 
     * @since 3.0
     */
    protected boolean runtime;

    /**
     * Creates an unnamed relationship.
     */
    public Relationship() {
    }

    /**
     * Creates a named relationship.
     */
    public Relationship(String name) {
        setName(name);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    /**
     * Returns relationship source entity.
     */
    public Entity getSourceEntity() {
        return sourceEntity;
    }

    /**
     * Sets relationship source entity.
     */
    public void setSourceEntity(Entity sourceEntity) {
        this.sourceEntity = sourceEntity;
    }

    /**
     * Returns a target entity of the relationship.
     */
    public abstract Entity getTargetEntity();

    /**
     * Sets relationship target entity. Internally calls <code>setTargetEntityName</code>.
     */
    public void setTargetEntityName(Entity targetEntity) {
        if (targetEntity != null) {
            setTargetEntityName(targetEntity.getName());
        } else {
            setTargetEntityName((String) null);
        }
    }

    /**
     * Returns the name of a target entity.
     */
    public String getTargetEntityName() {
        return targetEntityName;
    }

    /**
     * Sets the name of relationship target entity.
     */
    public void setTargetEntityName(String targetEntityName) {
        this.targetEntityName = targetEntityName;
    }

    /**
     * Returns a boolean value that determines relationship multiplicity. This defines
     * semantics of the connection between two nodes described by the source and target
     * entities. E.g. to-many relationship between two Persistent object classes means
     * that a source object would have a collection of target objects. This is a read-only
     * property.
     */
    public boolean isToMany() {
        return toMany;
    }

    public Object getParent() {
        return getSourceEntity();
    }

    public void setParent(Object parent) {
        if (parent != null && !(parent instanceof Entity)) {
            throw new IllegalArgumentException("Expected null or Entity, got: " + parent);
        }

        setSourceEntity((Entity) parent);
    }

    /**
     * Returns guaranteed non-null MappingNamespace of this relationship. If it happens to
     * be null, and exception is thrown. This method is intended for internal use by
     * Relationship class.
     */
    final MappingNamespace getNonNullNamespace() {
        Entity entity = getSourceEntity();

        if (entity == null) {
            throw new CayenneRuntimeException("Relationship '%s' has no parent Entity.", getName());
        }

        return entity.getNonNullNamespace();
    }

    /**
     * Overrides Object.toString() to return informative description.
     */
    @Override
    public String toString() {
        return new ToStringBuilder(this)
                .append("name", getName())
                .append("toMany", isToMany()).toString();
    }

    /**
     * @since 3.0
     */
    public boolean isRuntime() {
        return runtime;
    }

    /**
     * @since 3.0
     */
    public void setRuntime(boolean synthetic) {
        this.runtime = synthetic;
    }
    
    /**
     * Returns a "complimentary" relationship going in the opposite direction. Returns
     * null if no such relationship is found.
     * @since 3.1
     */
    public abstract Relationship getReverseRelationship();
    
    /**
     * Returns if relationship is mandatory
     * @since 3.1
     */
    public abstract boolean isMandatory();
}