javatools.db
Class DbFalseExpr

java.lang.Object
  |
  +--javatools.db.DbExpr
        |
        +--javatools.db.DbCriterion
              |
              +--javatools.db.DbFalseExpr

All Implemented Interfaces:

DbTableUser

public class DbFalseExpr

extends DbCriterion

An expression that always evaluates to false. If not optimised away by DbTrueExpr, it will probably result in "0 = 1" in the SQL.

The use of false expressions makes it very convenient for dynamically generated queries...

 DbExpr e = db.falseExpr();
 if (name != null) {
  e = e.or(table.getColumn("NAME")).equals(name));
 }
 if (age != null) {
  e = e.or(table.getColumn("AGE")).equals(age));
 }
 

This gets converted to...

 (0 = 1) OR ( NAME = ? ) OR ( AGE = ? )
 

and then DbOrExpr optimises this to...

 ( NAME = ? ) OR ( AGE = ? )
 

See Also:

DbOrExpr

Constructor Summary

DbFalseExpr(DbDatabase db)
Builds a new false expression.

Methods inherited from class javatools.db.DbCriterion

getQueryString, setSqlValues, usesTables

Methods inherited from class javatools.db.DbExpr

and, containsAllStrings, containsAllStrings, count, dateTrunc, equal, greaterThan, greaterThanOrEqual, in, in, isNotNull, isNull, lessThan, lessThanOrEqual, like, lower, max, min, notEqual, notIn, notIn, or, upper, usesTables

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DbFalseExpr

public DbFalseExpr(DbDatabase db)

Builds a new false expression.

Parameters:

db - The database that will be used.