Summary of all ways to extend server side logics in Frappe Framework

[kittiu]

Dear community,

I this thread I would like to summarize ways to extend server side logics in Frappe (python). This is based on my experiences thus far.

Till now, I only find 4 ways.

1. Use doc_event hooks
2. Class method extension
3. Whitelisted method override
4. Monkey patching

Note: #1 option is most recommended, #4 is least recommended.

1) Use doc_events hooks

This is the most used and recommended as it is easier to maintain than other methods.

https://frappeframework.com/docs/user/en/python-api/hooks#crud-events

Pros

• Works without overriding the original logic, it is an incremental work.
• Easy to use, recommended to use before other methods.

Cons

• Not as flexible as it should be,i.e., we can’t control the order of execution, nor prevent existing code from happening.
• Limited hook point such as validate, after_insert, on_update, etc…

2) Class method extension

This method is used to extend Class’s method only. It is flexible, the second best method.

https://frappeframework.com/docs/user/en/python-api/hooks#override-doctype-class

Pros

• Calling super() allows for better control over the order of code execution.
• Can be used with any method, not just CRUD like doc_events.
• This is the standard Python method.

Cons

• If there are 2 Downstream apps extending the same class, the latter will override the first.
• Can only be used with Class methods, can’t be used with floating functions

Note: If it’s a floating function, you have to use override type 3 or 4

3) Whitelisted method override

https://frappeframework.com/docs/user/en/python-api/hooks#override-whitelisted-methods

Pros

• Easy to use, it will directly override the whitelisted method

Cons

• It is an override, not an extension which I don’t really like it much.
• Can only be used with floating whitelisted methods (not Class’s whitelist methods)
• Can’t be used with non-whitelisted methods (which will need last resource, the monkey patch)

4) Monkey patch

This method must be said to be not the Framework’s approach, but in many cases it cannot be avoided (floating and non-whitelisted methods)

Pros

• It is the last ways

Disadvantages

• It is an override, not an extension
• Writing a patch in __ init __.py will work even if the app with this patch is not installed (if not installed, you have to delete it from the apps folder).

So, how you find this useful, and please correct me if there are better ways out there.

[brian_pond]

This is an excellent post; thank you for sharing!

I believe there is a 5) Server Script, which has similar capabilities to editing hooks.

Pros

• You make changes via a web browser, instead of hooks.py. This makes it a bit more accessible.

Disadvantages

• Your changes aren’t as visible/obvious. Another person who examines `hooks.py’ won’t see anything. They must remember to also go look in the Server Scripts. Comparing and contrasting what’s in there.

And I guess 6) would be Forking. I’ve had to do that sometimes, because what I needed to accomplish was too awkward or risky with Monkey Patching. Or because I just wanted an easy way to perform a diff between my code, versus official code.

[revant_one]

@brian_pond

And I guess 6) would be Forking

As soon as the official support for a version is stopped, it becomes easily forkable.

That means whoever is using less than v14 today can fork without any worry of diverging the code.

[kittiu]

For the monkey patch part, which has a flaw that it is loaded withtout installation.

I think here is the solution as I tested it

How can we override ERPNext core functions?

FYI, you can also use monkey patching with Python. I needed to override erpnext.controllers.taxes_and_totals.calculate_taxes_and_totals. Here is what I did: Create a new module called my_app.my_module and a file inside it called override_calculate_taxes_and_totals.py with a new class like this: from erpnext.controllers import taxes_and_totals class my_app_calculate_taxes_and_totals( taxes_and_totals.calculate_taxes_and_totals ): """Override for calculating taxes and totals in My…

[Peer]

There is also System Console which might be useful for one-off interventions with specialized code, or even stuff done from time to time only (made more useable and sustainable with documenting it with your own SOPs [Standard Operation Procedures]).

Also very useful for testing code-bits and getting things right.

Great for getting imports to work.

It has a log so you can re-check later if you forgot code that worked, etc.

[szufisher]

Yes, I used system console quite a lot to debug python script.

[kittiu]

How do you mean by this? Any simple example?

[Peer]

It’s not clear whom you mean by “you” and what you mean by “this”. Anyway,

if you want an example for system console, just type “system console” (or the appropriate translation according to your setup) in awesomebar and see what you get. Then run one of the simplest of python code, something like

print('Hello World')

then hit Execute button and see the output below on the page.
To the left of the Execute Button there is another one to open the Logs of what you run.

See the documentation for the Python Script API to get an idea of what you can run in this console, it has certain limitations which you will run into at some point if you know python.

The System Console resembles Server Script, but the latter are linked to certain actions which need to happen for server scripts to run, whereas in the System Console you run your code similarly to a REPL.