在Form中展示的data source中的数据需要根据另一张table的field进行条件过滤的时候，可以考虑使用QueryBuildDataSource
在Form的data source的table中覆盖init()方法，在根据需求考虑在super()前还是super()后编写代码

QueryBuildLink          qbl;

QueryBuildDataSource    custTableQBDS, custTransQBDS;

custTableQBDS = query.addDataSource(tablenum(custTable));

custTransQBDS = custTableQBDS.addDataSource(tableNum(CustTrans));

qbl = custTransQBDS.addLink(fieldNum(CustTable, AccountNum), fieldNum(CustTrans, AccountNum));
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public void init()
{
    QueryBuildDataSource    qbds;

    super();

    qbds = this.query().dataSourceTable(tableNum(
                    Table1)).addDataSource(
                     tableNum(Table2));
    qbds.addLink(fieldNum(Table1,CompanyId), 
        fieldNum(Table2, CompanyID));

    qbds.joinMode(JoinMode::ExistsJoin);
}
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