Class ForeignKeyField

src/src/com/orm/androrm/field/ForeignKeyField.java:42–180

The foreign key field can be used to build a relation between two models. One model can create a link to another model by using a foreign key. The type parameter is used to determine the linked model type. @author Philipp Giese @param Type of the linked model.

 * @param <T>	Type of the linked model. 
 */
public class ForeignKeyField<T extends Model> extends DataField<T> implements Relation<T> {

	private Class<T> mTarget;
	private int mReference;
	private boolean mOnDeleteCascade;
	
	/**
	 * Initializes a new foreign key field. The target
	 * parameter is used to determine the class of the 
	 * linked model in order to create the correct 
	 * constraints. 
	 * 
	 * @param target	Class of the linked model. 
	 */
	public ForeignKeyField(Class<T> target) {
		mTarget = target;
		mOnDeleteCascade = true;
	}
	
	/**
	 * By default foreign key fields have the option
	 * ON DELETE CASCADE set. This means if the model 
	 * this field is pointing to will be deleted, also 
	 * the referencing model will be deleted. 
	 * <br /><br />
	 * 
	 * By calling doNotCascade on the field you can 
	 * prevent this behavior. 
	 */
	public void doNotCascade() {
		mOnDeleteCascade = false;
	}
	
	/**
	 * As foreign keys may require database access in order to 
	 * get their value, you have to use this function. The
	 * regular {@link DataField#get()} won't work at all times. 
	 * 
	 * @param context	{@link Context} of the application.
	 * 
	 * @return	An instance of the references model or <code>null</code>
	 * 			if nothing could be found. 
	 */
	public T get(Context context) {
		if(mValue == null) {
			return Model.objects(context, mTarget).get(mReference);
		}
		
		return mValue;
	}

	/**
	 * Creates the foreign key constraint for the database. 
	 * 
	 * @param fieldName name of the field, that references the
	 * 					other table.
	 * 
	 * @return The constraint.