[Link]

    Query                   q;   
    QueryBuildDataSource    qB;
    QueryBuildDataSource    qB2; 
    QueryBuildDataSource    qB3;
    ;
    qB  = q.addDataSource(tablenum(AssetBookTable));
    qB.addRange(Fieldnum(AssetBookTable,CurrentOperationsTax)).value(enum2value(currentOperationsTax));
    qB2 = qB.addDataSource(tablenum(AssetBook));
    qB2.addLink(FieldNum(AssetBookTable,BookId),fieldNum(AssetBook,BookId));
    qB2.addRange(Fieldnum(AssetBook,AssetId)).value(assetId);
    qB2.joinMode(JoinMode::OuterJoin); 
//(а так же NoExistsJoin, InnerJoin, EXISTSJOIN);
    qB3 = qB2.addDataSource(tablenum(AssetBookTable));
    qB3.addLink(FieldNum(AssetBook,BookId),fieldNum(AssetBookTable,BookId));