Saturday, May 27, 2017

Pivot charts in LibreOffice: Final part 3

It has been a while when I posted an update on pivot charts. In the mean time I finished what was planned and iterated through cycles of needed fixes and polish. In the mean time we branched off the code for LibreOffice 5.4 and the pivot chart implementation is part of that too. If you want to try it out, you can get the LibreOffice 5.4 pre-release on the download page.

Pivot chart field button actions

Last time I explained about the buttons, but I didn't explain what action is performed when we click on them. The buttons generally have a similar function as in pivot table - to show the pivot table layout and to apply filtering of data. The filtering in the pivot table opens a non-modal windows where you can choose the filtering. For pivot charts I wanted to reuse that, so when clicking on the field button, the request is send from the Chart component back to the Calc, where the same window is shown (shown in Figure 1).

Figure 1: Pivot chart field filter

Improvements to pivot chart buttons

In previous post, the pivot chart field buttons were still very basic. Now I improved them, so they show a down arrow, so they look more like they have a pop-up action attached to them. If there is some filtering applied, then the arrow turns blue (similar to the pivot table), so it is easier to see when a field has any filter applied. 
For page fields we also show what is filtered: when nothing is filtered "- all -" is shown, when some all filtered, then "- multiple -" is shown and when only one value is not filtered, then we show that value.

ODF support and compatibility

A pivot chart is useless if we can't save it to a file and later reopen. For this it was needed to extend the ODF format. Luckily, this was relatively easy to do, as the only thing needed is the name of the pivot table that a chart links to (I added "data-pilot-source" attribute to "chart:chart" element). Everything else is already present in the existing import/export code so no additional elements were needed to recreate the exact state that was present when the document was saved. 

A bit related is also copy and paste, which uses the ODF as an intermediate format (copy saves parts to the ODF format and paste loads the format) so things like copy/paste between documents works. A difference here is that we can copy the pivot chart and paste to a different (empty) document, which doesn't have the pivot table. In this case I had to make sure that a normal chart is pasted, which uses the table internal data and not the pivot table. The table internal data is always written with the chart object even if it is not used, just for situations like this (another one is also when we copy from Calc document and paste in Writer document).


It would be really hard for me to implement this properly without tests, as they cemented the behaviour and, if they failed, I knew that probably I made a mistake or I have took a wrong approach to solve the problem. First I added a import / export tests, which just used an existing document to get the data, pivot table and already existing pivot chart. The purpose of these are to test the ODF import and export code. 
Later, I added tests which programatically add data into a sheet and create a pivot table from scratch as a set-up, then create the pivot chart and test various pivot table layouts, and assert what we expect to see in a pivot chart. This approach is better as a document is not needed, and it demonstrates that a pivot chart can be made from scratch with the available API.

Final demo

Finally, I want to show the complete demo of the pivot chart feature:

You can find the video on YouTube at the following URL:


Many thanks to Nantes Métropole and Ville de Nantes for making this work possible.

Read more about Nantes deployment here.

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