/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
 */
package org.hibernate.criterion;

import java.io.Serializable;

import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.type.Type;

An object-oriented representation of a query result set projection in a Criteria query. Built-in projection types are provided by the Projections factory class. This interface might be implemented by application classes that define custom projections. 
Author:
Gavin King, Steve Ebersole
See Also:
Projections
Criteria/**
 * An object-oriented representation of a query result set projection  in a {@link Criteria} query.
 * Built-in projection types are provided  by the {@link Projections} factory class.  This interface might be
 * implemented by application classes that define custom projections.
 *
 * @author Gavin King
 * @author Steve Ebersole
 *
 * @see Projections
 * @see Criteria
 */
public interface Projection extends Serializable {

	
Render the SQL fragment to be used in the SELECT clause.
Params:
criteria – The local criteria to which this project is attached (for resolution).
position – The number of columns rendered in the SELECT clause before this projection.  Generally
speaking this is useful to ensure uniqueness of the individual columns aliases.
criteriaQuery – The overall criteria query instance.
Throws:
HibernateException – Indicates a problem performing the rendering
Returns:
The SQL fragment to plug into the SELECT/**
	 * Render the SQL fragment to be used in the <tt>SELECT</tt> clause.
	 *
	 * @param criteria The local criteria to which this project is attached (for resolution).
	 * @param position The number of columns rendered in the <tt>SELECT</tt> clause before this projection.  Generally
	 * speaking this is useful to ensure uniqueness of the individual columns aliases.
	 * @param criteriaQuery The overall criteria query instance.
	 * @return The SQL fragment to plug into the <tt>SELECT</tt>
	 * @throws HibernateException Indicates a problem performing the rendering
	 */
	public String toSqlString(Criteria criteria, int position, CriteriaQuery criteriaQuery)
			throws HibernateException;

	
Render the SQL fragment to be used in the GROUP BY clause
Params:
criteria – The local criteria to which this project is attached (for resolution).
criteriaQuery – The overall criteria query instance.
Throws:
HibernateException – Indicates a problem performing the rendering
Returns:
The SQL fragment to plug into the GROUP BY/**
	 * Render the SQL fragment to be used in the <tt>GROUP BY</tt> clause
	 *
	 * @param criteria The local criteria to which this project is attached (for resolution).
	 * @param criteriaQuery The overall criteria query instance.
	 * @return The SQL fragment to plug into the <tt>GROUP BY</tt>
	 * @throws HibernateException Indicates a problem performing the rendering
	 */
	public String toGroupSqlString(Criteria criteria, CriteriaQuery criteriaQuery)
			throws HibernateException;

	
Types returned by the rendered SQL fragment. In other words what are the types that would represent the values this projection asked to be pulled into the result set? 
Params:
criteria – The local criteria to which this project is attached (for resolution).
criteriaQuery – The overall criteria query instance.
Throws:
HibernateException – Indicates a problem resolving the types
Returns:
The return types./**
	 * Types returned by the rendered SQL {@link #toSqlString fragment}.  In other words what are the types
	 * that would represent the values this projection asked to be pulled into the result set?
	 *
	 * @param criteria The local criteria to which this project is attached (for resolution).
	 * @param criteriaQuery The overall criteria query instance.
	 * @return The return types.
	 * @throws HibernateException Indicates a problem resolving the types
	 */
	public Type[] getTypes(Criteria criteria, CriteriaQuery criteriaQuery)
			throws HibernateException;

	
Get the return types for a particular user-visible alias.
 Differs from getTypes(Criteria, CriteriaQuery) in that here we are only interested in the types related to the given criteria-level alias. 
Params:
alias – The criteria-level alias for which to find types.
criteria – The local criteria to which this project is attached (for resolution).
criteriaQuery – The overall criteria query instance.
Throws:
HibernateException – Indicates a problem resolving the types
Returns:
The return types; expected to return null if this projection does not understand this alias./**
	 * Get the return types for a particular user-visible alias.
	 * <p/>
	 * Differs from {@link #getTypes(org.hibernate.Criteria, CriteriaQuery)} in that here we are only interested in
	 * the types related to the given criteria-level alias.
	 *
	 * @param alias The criteria-level alias for which to find types.
	 * @param criteria The local criteria to which this project is attached (for resolution).
	 * @param criteriaQuery The overall criteria query instance.
	 * @return The return types; expected to return null if this projection does not understand this alias.
	 * @throws HibernateException Indicates a problem resolving the types
	 */
	public Type[] getTypes(String alias, Criteria criteria, CriteriaQuery criteriaQuery)
			throws HibernateException;


	
Get the SQL column aliases used by this projection for the columns it writes for inclusion into the
SELECT clause (toSqlString. Hibernate always uses column aliases to extract data from the JDBC ResultSet, so it is important that these be implemented correctly in order for Hibernate to be able to extract these val;ues correctly. 
Params:
position – Just as in toSqlString, represents the number of columns rendered
prior to this projection.
Returns:
The columns aliases./**
	 * Get the SQL column aliases used by this projection for the columns it writes for inclusion into the
	 * <tt>SELECT</tt> clause ({@link #toSqlString}.  Hibernate always uses column aliases to extract data from the
	 * JDBC {@link java.sql.ResultSet}, so it is important that these be implemented correctly in order for
	 * Hibernate to be able to extract these val;ues correctly.
	 *
	 * @param position Just as in {@link #toSqlString}, represents the number of <b>columns</b> rendered
	 * prior to this projection.
	 * @return The columns aliases.
	 */
	public String[] getColumnAliases(int position);

	
Get the SQL column aliases used by this projection for the columns it writes for inclusion into the
SELECT clause (toSqlString for a particular criteria-level alias.
Params:
alias – The criteria-level alias
position – Just as in toSqlString, represents the number of columns rendered
prior to this projection.
Returns:
The columns aliases pertaining to a particular criteria-level alias; expected to return null if
this projection does not understand this alias./**
	 * Get the SQL column aliases used by this projection for the columns it writes for inclusion into the
	 * <tt>SELECT</tt> clause ({@link #toSqlString} <i>for a particular criteria-level alias</i>.
	 *
	 * @param alias The criteria-level alias
	 * @param position Just as in {@link #toSqlString}, represents the number of <b>columns</b> rendered
	 * prior to this projection.
	 * @return The columns aliases pertaining to a particular criteria-level alias; expected to return null if
	 * this projection does not understand this alias.
	 */
	public String[] getColumnAliases(String alias, int position);

	
Get the criteria-level aliases for this projection (ie. the ones that will be passed to the ResultTransformer) 
Returns:
The aliases/**
	 * Get the criteria-level aliases for this projection (ie. the ones that will be passed to the
	 * {@link org.hibernate.transform.ResultTransformer})
	 *
	 * @return The aliases
	 */
	public String[] getAliases();

	
Is this projection fragment (SELECT clause) also part of the GROUP BY
Returns:
True if the projection is also part of the GROUP BY; false otherwise./**
	 * Is this projection fragment (<tt>SELECT</tt> clause) also part of the <tt>GROUP BY</tt>
	 *
	 * @return True if the projection is also part of the <tt>GROUP BY</tt>; false otherwise.
	 */
	public boolean isGrouped();

}