Filter records in form by code

Courtesy: http://dynamics-ax-live.blogspot.com/2010/03/how-to-filter-records-in-form-by-code.html
Step 1: Declare a class variable
In the ClassDeclaration method of the form, define a range.

QueryBuildRange CurrencyQBR;

Step 2: Instantiate the new range.
In the init method on the datasource of the form, you assign the range to a specific field (after the super call).

public void init()
{
super();

CurrencyQBR = this.query().dataSourceName('CustTable').addRange(fieldnum(CustTable,Currency));
}

Step 3: In the last step, you assign a value to the range.
This is done in the executeQuery method on the same datasource of the form. Before the super call. Like this:

public void executeQuery()
{ ;

CurrencyQBR.value(queryvalue('USD'));

super();
}