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Relational Persistence for Java
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//$Id: Projections.java 6970 2005-05-31 20:24:41Z oneovthafew $
package org.hibernate.criterion;

import org.hibernate.type.Type;

/**
 * The criterion package may be used by applications as a framework for building
 * new kinds of Projection. However, it is intended that most applications will
 * simply use the built-in projection types via the static factory methods of this class.

 * 

 * The factory methods that take an alias allow the projected value to be referred to by 
 * criterion and order instances.
 *
 * @see org.hibernate.Criteria
 * @see Restrictions factory methods for Criterion instances
 * @author Gavin King
 */
public final class Projections {

	private Projections() {
		//cannot be instantiated
	}
	
	/**
	 * Create a distinct projection from a projection
	 */
	public static Projection distinct(Projection proj) {
		return new Distinct(proj);
	}
	
	/**
	 * Create a new projection list
	 */
	public static ProjectionList projectionList() {
		return new ProjectionList();
	}
		
	/**
	 * The query row count, ie. count(*)
	 */
	public static Projection rowCount() {
		return new RowCountProjection();
	}
	
	/**
	 * A property value count
	 */
	public static CountProjection count(String propertyName) {
		return new CountProjection(propertyName);
	}
	
	/**
	 * A distinct property value count
	 */
	public static CountProjection countDistinct(String propertyName) {
		return new CountProjection(propertyName).setDistinct();
	}
	
	/**
	 * A property maximum value
	 */
	public static AggregateProjection max(String propertyName) {
		return new AggregateProjection("max", propertyName);
	}
	
	/**
	 * A property minimum value
	 */
	public static AggregateProjection min(String propertyName) {
		return new AggregateProjection("min", propertyName);
	}
	
	/**
	 * A property average value
	 */
	public static AggregateProjection avg(String propertyName) {
		return new AvgProjection(propertyName);
	}
	
	/**
	 * A property value sum
	 */
	public static AggregateProjection sum(String propertyName) {
		return new AggregateProjection("sum", propertyName);
	}
	
	/**
	 * A SQL projection, a typed select clause fragment
	 */
	public static Projection sqlProjection(String sql, String[] columnAliases, Type[] types) {
		return new SQLProjection(sql, columnAliases, types);
	}
	
	/**
	 * A grouping SQL projection, specifying both select clause and group by clause fragments
	 */
	public static Projection sqlGroupProjection(String sql, String groupBy, String[] columnAliases, Type[] types) {
		return new SQLProjection(sql, groupBy, columnAliases, types);
	}

	/**
	 * A grouping property value
	 */
	public static PropertyProjection groupProperty(String propertyName) {
		return new PropertyProjection(propertyName, true);
	}
	
	/**
	 * A projected property value
	 */
	public static PropertyProjection property(String propertyName) {
		return new PropertyProjection(propertyName);
	}
	
	/**
	 * A projected identifier value
	 */
	public static IdentifierProjection id() {
		return new IdentifierProjection();
	}
	
	/**
	 * Assign an alias to a projection, by wrapping it
	 */
	public static Projection alias(Projection projection, String alias) {
		return new AliasedProjection(projection, alias);
	}
}