Question

I have this Birt report that I inherited from another developer, consisting of a child table inside a master table. For each row in the master table, the child table lists items belonging to the current master row item.

The two tables are fed from different data sets, the child table dataset taking a parameter indicating the master item whose child items to fetch.

Now, what I need to do is add a SUM aggregate to the bottom of the master table, showing the total (for all master items) of a certain field in the child table.

Consider, for example, the following data:

MasterItem1
            ChildItem1 SomeValue
            ChildItem2 SomeValue
            ChildItem3 SomeValue
MasterItem2
            ChildItem1 SomeValue
            ChildItem2 SomeValue
            ChildItem3 SomeValue
--------------------------------
                       Total

(Why wasn’t this done with grouping instead? Short answer: There are in fact two child tables to each master row, containing different numers and types of fields, so the previous developer probably didn’t figure out a way to accomplish this with grouping.)

At first I thought I could simply add another child table inside the Total field, with an aggregate summing up the values from the child dataset. That didn’t work, however, since the child dataset requires a parameter indicating the master item whose children to fetch, so there is no way to get ALL values from the child dataset at once.

I’m thinking there might be a way to create an expression that references the SomeValue fields in the child table directly, instead of going through the child data set.

Any suggestions are greatly appreciated.

Answer 1

Thanks Mark and Mystik, both your answers led me on the right path!

My final solution is as follows:

1) Declare the sum-variable in the initialize method for the report:

var total = 0;

2) Add each row’s value to the sum-variable in the onReder method of the data field containing the values:

total += parseInt(this.getValue());

3) Use the sum-variable as expression in the total-field.

Works like a charm.

---

Update:
Found a bug in my solution: the last line was left out of the sum. I think the value of the total-cell in the table footer is being defined before the last line has been rendered.

Fix:

1. Moved summing code from onRender method to onCreate

2. Added the following code to the total-cell’s onRender method:

   this.setDisplayValue(total);