I am going to share through post that sometimes we need to retrieve the number of records in a particular datasource. Let's say we have two datasources in a form named Student and StudentCourseEnrollment.

I simply need to fetch the number of records in Student Datasource in the init event of the the form. I would require following peace of code for that.

public void init()
    QueryRun queryRun;


    queryRun = new QueryRun(Student_ds.query());

    info(strfmt("Total Records in Student Datasource %1",SysQuery::countTotal(queryRun)));


Further you can refer this post to retrieve the rows from the temporary data source as well.