Thank you a lot.
I was on the right track, the updateRow method of the igDataSource did the job.
The only thing I had changed was the autoCommit:bool  set to false.
Now the stuff is in the transaction log 

Thank you a lot,
I have one question left.
Currently the GUI is working very well, in my grid one column has numeric editors, combo and checkox editors.
My problem is the connection of this editors and the grid. When i change the state of the checkbox, the checkbox change the value, but how will this change the value in the datasource of my grid?
I tried already to update the datasource with the event "valueChanged" of the Checkbox editor. But when I change the values of the datasource, the array of datasource.pendingTransactions() is still empty. I used the updateRow function of the datasource for the changing the value.
What is the best way to let the editors deal with the grid/datasource?

Hello Vasil Pavlov,thank you a lot for your post. It solves all my problems, very good example and hyperlinks