How to override Decidim core logic

[ahukkanen]

Many times we need to do some small changes to Decidim logic within the instances. E.g. removing the steps from proposal creation, adding new fields to admin forms, making some required field optional, etc.

Decidim core logic can be overridden in few different ways within an instance:

1. Copying and pasting the original controllers, commands, forms, etc. and changing them directly from your application
2. Creating concerns and applying them to these layers to override only the parts that you need to touch

Both are valid and fine ways but they have their own benefits and disadvantages.

For the first one, the advantage is that it's rather easy to do this and you can get it done quickly what you need to accomplish. The disadvantage is that after you upgrade Decidim, you need to keep all these files in sync with the core updates.

For the second one, the advantage is that it is easier to keep these changes in sync with core updates than in the first approach. The disadvantage is that you need to learn about monkey patching, concerns (and include blocks), initializers, initialization order, etc.

Our suggestion would be to document both of these methods and start with the first approach. Once accomplised what needs to be accomplished using the first approach, convert it to the "better" way, i.e. the second approach.

[ahukkanen]

As @sinaeftekhar is doing this right now, I think he can also write some docs about this after he finishes with the task.

[andreslucena]

We have a few lines here: https://docs.decidim.org/en/customize/code/ - but of course we should improve it much more! Specially now that we have lots of real world examples.

The disadvantage is that after you upgrade Decidim, you need to keep all these files in sync with the core updates.

Sometime ago I found this spec for tackling this same problem.

[microstudi]

Sometime ago I found this spec for tackling this same problem.

I use this kind of approach to keep track of changes. I'd recommend to document that as well as a recomendation if you want to override things. I'd gladly contribute to this piece of documentation once started i you want.

[ahukkanen]

This has been already implemented by @sinaeftekhar through decidim/decidim#9325.

The page is live at:
https://docs.decidim.org/en/customize/logic.html

This was what we needed for our own use, so I'll close this issue. If anyone wants to add to that or make some further guidance, feel free to contribute to that page!