lookup with joining two tables in AX 2012

This code in the lookup() method.

The same code can be written in three places to achieve the lookup.
1) Under AOT->Table->Method and cal this method from the form design where you want to display the lookup.
2) Form->Datasource->Table->Field->method
3) Form->Design->Field->Method.

public void lookup()
{
Query query = new Query();
QueryBuildDataSource qbds;
QueryBuildDataSource QbdsJoin;

// Instantiate sysTableLookup object using table which will provide the visible fields
SysTableLookup sysTableLookup = sysTableLookup::newParameters(tableNum(TableName), this);
;

// Create the query.
qbds= query.addDataSource(tableNum(TableName));
qbds.addRange(fieldNum(TableName, FieldName)).value('Value');

//Join Table
QbdsJoin= qbds.addDataSource(tableNum(TableName2));
QbdsJoin.relations(true);
QbdsJoin.joinMode(JoinMode::ExistsJoin);
QbdsJoin.addRange(fieldNum(TableName2, Fieldname)).value('Value');

// Set the query to be used by the lookup form
sysTableLookup.parmQuery(query);

// Specify the fields to show in the form.
sysTableLookup.addLookupfield(fieldNum(TableName, FiledName));
sysTableLookup.addLookupfield(fieldId2Ext(fieldNum(TableName, Dimension), 1));

// Perform the lookup
sysTableLookup.performFormLookup();
}