org.apache.empire.db.expr.column.DBCountExpr Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.empire.db.expr.column;
// Java
import org.apache.empire.data.DataType;
import org.apache.empire.db.DBColumn;
import org.apache.empire.db.DBColumnExpr;
import org.apache.empire.db.DBDatabase;
import org.apache.empire.db.DBRowSet;
import org.apache.empire.xml.XMLUtil;
import org.w3c.dom.Element;
import java.util.Set;
/**
* This class is used to add the "count" statement to the SQL-Command.
*
* There is no need to explicitly create instances of this class.
* Instead use {@link DBRowSet#count() or @link DBColumnExpr#count() }
*
*
*/
public class DBCountExpr extends DBColumnExpr
{
private final static long serialVersionUID = 1L;
private final DBRowSet rowset;
private final DBColumnExpr column;
private final boolean distinct;
/**
* Constructs a DBCountExpr.
*
* @param rowset the rowset
*/
public DBCountExpr(DBRowSet rowset)
{
this.rowset = rowset;
this.column = null;
this.distinct = false;
}
/**
* Constructs a DBCountExpr.
*
* @param expr the column
* @param distinct set true for distinct count
*/
public DBCountExpr(DBColumnExpr expr, boolean distinct)
{
this.rowset = null;
this.column = expr;
this.distinct = distinct;
}
/**
* Returns the current DBDatabase object.
*
* @return the current DBDatabase object
*/
@Override
public DBDatabase getDatabase()
{
if (column!=null)
return column.getDatabase();
else
return rowset.getDatabase();
}
/**
* Returns the data type: DT_INTEGER.
*
* @return the data type: DT_INTEGER
*/
@Override
public DataType getDataType()
{
return DataType.INTEGER;
}
/**
* Returns the String "count".
*
* @return the String "count"
*/
@Override
public String getName()
{
return "count";
}
/**
* Returns null.
*
* @return null
*/
@Override
public DBColumn getUpdateColumn()
{
return null;
}
/**
* Returns true since the count function is an aggregate function.
*
* @return always true
*/
@Override
public boolean isAggregate()
{
return true;
}
/**
* @see org.apache.empire.db.DBExpr#addReferencedColumns(Set)
*/
@Override
public void addReferencedColumns(Set list)
{
if (column!=null)
column.addReferencedColumns(list);
else
list.add(rowset.getColumn(0)); // select any column
}
/**
* Creates the SQL-Command adds the String "count(*)" to the SQL-Command.
*
* @param sql the SQL-Command
* @param context the current SQL-Command context
*/
@Override
public void addSQL(StringBuilder sql, long context)
{
sql.append("count(");
if (column!=null)
{ // count(distinct column)
if (distinct)
sql.append("distinct ");
column.addSQL(sql, (context & ~CTX_ALIAS));
}
else
{ // count(*)
sql.append("*");
}
sql.append(")");
}
/**
* this adds the column description to the parent element
*/
@Override
public Element addXml(Element parent, long flags)
{ // Add Expression
Element elem;
if (column!=null)
{ elem = column.addXml(parent, flags);
}
else
{ elem = XMLUtil.addElement(parent, "column");
elem.setAttribute("name", getName());
}
elem.setAttribute("function", "count");
// done
return elem;
}
}