Hello, i've done many researches but i can't find anything on how to use this domain filter.

I would like to show, in my tree view, the records that only has a field 'fieldO2M' not empty.

For now, I find this incredibly hard to understand how domain works. I tried several things, the only one that went close to my goal was :

This one works but doesn't do what i want, it make the value of the field on which it is applied disappear. I want the all line to not be shown just like if i had used filter --> "fieldO2M" is defined.

After this I tried a lot of things that looks like this :

But nothing that works or actually do something on my view.
Can someone explains me how the domain attribute works and how can I achieve my goal ?

I know that the domain definition is [('field','operation',value)] but i don't understand how to apply it to a field.

Thank you in advance ! :)