javatools.db
Class DbTrueExpr

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

public class DbTrueExpr

extends DbCriterion

An expression that always evaluates to true. If not optimised away but DbAndExpr, this will probably result in "0 = 0" in the SQL.

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

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

This gets converted to...

  (0 = 0) AND ( NAME = ? ) AND ( AGE = ? )
  

and then DbAndExpr optimises this to...

  ( NAME = ? ) AND ( AGE = ? )
  

See Also:

DbAndExpr

Field Summary

Fields inherited from class javatools.db.DbCriterion

c1, c2, op

Fields inherited from class javatools.db.DbExpr

db

Constructor Summary

DbTrueExpr(DbDatabase db)

Methods inherited from class javatools.db.DbCriterion

getQueryString, setSqlValues, usesTables

Methods inherited from class javatools.db.DbExpr

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

Methods inherited from class java.lang.Object

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

Constructor Detail

DbTrueExpr

public DbTrueExpr(DbDatabase db)