What is the actual use of ActiveRecord::SpawnMethods#except ?

[Arup Rakshit]

I really don't understand the actual usecase of the *except* method
http://api.rubyonrails.org/classes/ActiveRecord/SpawnMethods.html#method-i-except

If I don't want a condition to apply in my _query_, then why should I add it?
After adding a condition, what is the point of removing it again. This how the
doco http://api.rubyonrails.org/classes/ActiveRecord/SpawnMethods.html#method-i-except is saying.

--
================
Regards,
Arup Rakshit
================
Debugging is twice as hard as writing the code in the first place. Therefore,
if you write the code as cleverly as possible, you are, by definition, not
smart enough to debug it.

--Brian Kernighan

[Matt Jones]

On Saturday, 5 July 2014 02:33:14 UTC-5, Arup Rakshit wrote:

I really don't understand the actual usecase of the *except* method
http://api.rubyonrails.org/classes/ActiveRecord/SpawnMethods.html#method-i-except

If I don't want a condition to apply in my _query_, then why should I add it?
After adding a condition, what is the point of removing it again. This how the
doco http://api.rubyonrails.org/classes/ActiveRecord/SpawnMethods.html#method-i-except is saying.

`except` is used when you want to use part of a relation but not necessarily the whole thing. It's not always useful in application code, but when dealing with generic relations it can be really useful:

https://github.com/rails/rails/blob/44b7d6c41610bb8ddd058b3815543985f65bf7ad/activerecord/lib/active_record/relation/finder_methods.rb#L296

Here, `except` is used to remove parts of the relation that `exists?` doesn't want to use.

--Matt Jones 

[Arup Rakshit]

> `except` is used when you want to use part of a relation but not
> necessarily the whole thing. It's not always useful in application code,
> but when dealing with generic relations it can be really useful:
>
> https://github.com/rails/rails/blob/44b7d6c41610bb8ddd058b3815543985f65bf7ad
> /activerecord/lib/active_record/relation/finder_methods.rb#L296
>
> Here, `except` is used to remove parts of the relation that `exists?`
> doesn't want to use.
>
> --Matt Jones

Very useful example. Does it mean, we can use it also *scope* or on *default
scope* ? Will it be a good choice although to use scope relation if it fits any
query, with some tailoring using *except* ?

[Matt Jones]

On Sunday, 6 July 2014 13:29:15 UTC-5, Arup Rakshit wrote:

> `except` is used when you want to use part of a relation but not
> necessarily the whole thing. It's not always useful in application code,
> but when dealing with generic relations it can be really useful:
>
> https://github.com/rails/rails/blob/44b7d6c41610bb8ddd058b3815543985f65bf7ad
> /activerecord/lib/active_record/relation/finder_methods.rb#L296
>
> Here, `except` is used to remove parts of the relation that `exists?`
> doesn't want to use.
>
> --Matt Jones

Very useful example. Does it mean, we can use it also *scope* or on *default
scope* ? Will it be a good choice although to use scope relation if it fits any
query, with some tailoring using *except* ?

Yep. There are also some related methods; `rewhere`, `reorder`, and `unscope`. They allow somewhat finer control than `except`.

--Matt Jones