@DenisChenu Feel free to leave feedback. Current discussion about how to increase testability of the code-base, in this case our models.

Why not , but i need to learn clean difference between services and dao … a sample is OK :)

E.g., if you have a method in a class with no "this" and no "self" (and it's static even), one should consider moving it to a service class. What's the difference between a helper function and a service class? A service class can be mocked in a test, meaning that if class A depend on service class B, we can create a dummy class B_dummy when testing A. This is not possible for helper functions (although a function is easier to test than a stateful class).

We have a lot of Service in current models ?

Just some definition ? No ?

Consider copyToCentral method: https://github.com/LimeSurvey/LimeSurvey/blob/master/application/controllers/admin/participantsaction.php#L2307

It is thin, which is good. Basically just dealing with the outside world (request) and delegating work to another class. BUT: That class is an active record model, which is bullshit. Active records should ONLY deal with database input/output. What we need is a layer between models and controllers which can more easily be tested than a controller action. So this method here should be moved to a CPDBCopyService class: https://github.com/LimeSurvey/LimeSurvey/blob/master/application/models/Participant.php#L1941

So instead of "thin controllers, fat models" pattern, it should be "thin controllers, thin models, thin services". :)

All our helper functions could be moved into services, too. But that's another topic.

Right for copyToCentral … (me never really work with CPDB …)
And better understand here :)

And Survey::replacePolicyLink where is the best place ?

New class SurveyPolicyService

Btw, "dao" folder should maybe be called "activerecords". Service can inherit from Yii CModel class (not sure what it does, honestly).

Service can inherit from Yii CModel class

Or maybe not, since a service doesn't hold so much data (state).

A third folder called "forms" or "formmodels" would also be good.

A third folder called "forms" or "formmodels" would also be good.

Yep :)

Then another possibility:

models/
    forms/
        InstallerForm...
    activerecords/
        User...
services/
    SurveyPolicyService

Putting services outside of model folder since they don't inherit from CModel.