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How does ActiveRecord::Relation get added to Rails' models and why does each model have individual Relation class?

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1

Suppose I have a Rails model: class Project < ActiveRecord::Base

In the Rails console:

> Project.all
=> #<ActiveRecord::Relation []>

That seems reasonable. However,

> Project.all.class
=> Project::ActiveRecord_Relation

What is Project::ActiveRecord_Relation? Specifically,

• How did it get "added" (namespaced into) to my model class?


• How does it respond to is_a? correctly? Project.all.is_a?(ActiveRecord::Relation) returns true (which is expected), but is Project::ActiveRecord_Relation actually an instance of ActiveRecord::Relation, or is it something else?


• Why do this? Why doesn't Project.all return an ActiveRecord::Relation, rather than Project::ActiveRecord_Relation?

(This is in the context of Rails 5.1, in case it's changed in older or newer versions.)

(I'm open to title edits if someone else can come up with a better title for this question)

ruby-on-rails ruby activerecord

share|improve this question

edited Mar 22 at 21:18

chumakoff

4,31911233

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

add a comment | 

1

Suppose I have a Rails model: class Project < ActiveRecord::Base

In the Rails console:

> Project.all
=> #<ActiveRecord::Relation []>

That seems reasonable. However,

> Project.all.class
=> Project::ActiveRecord_Relation

What is Project::ActiveRecord_Relation? Specifically,

• How did it get "added" (namespaced into) to my model class?


• How does it respond to is_a? correctly? Project.all.is_a?(ActiveRecord::Relation) returns true (which is expected), but is Project::ActiveRecord_Relation actually an instance of ActiveRecord::Relation, or is it something else?


• Why do this? Why doesn't Project.all return an ActiveRecord::Relation, rather than Project::ActiveRecord_Relation?

(This is in the context of Rails 5.1, in case it's changed in older or newer versions.)

(I'm open to title edits if someone else can come up with a better title for this question)

ruby-on-rails ruby activerecord

share|improve this question

edited Mar 22 at 21:18

chumakoff

4,31911233

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

add a comment | 

Suppose I have a Rails model: class Project < ActiveRecord::Base

In the Rails console:

> Project.all
=> #<ActiveRecord::Relation []>

That seems reasonable. However,

> Project.all.class
=> Project::ActiveRecord_Relation

What is Project::ActiveRecord_Relation? Specifically,

• How did it get "added" (namespaced into) to my model class?


• How does it respond to is_a? correctly? Project.all.is_a?(ActiveRecord::Relation) returns true (which is expected), but is Project::ActiveRecord_Relation actually an instance of ActiveRecord::Relation, or is it something else?


• Why do this? Why doesn't Project.all return an ActiveRecord::Relation, rather than Project::ActiveRecord_Relation?

(This is in the context of Rails 5.1, in case it's changed in older or newer versions.)

(I'm open to title edits if someone else can come up with a better title for this question)

ruby-on-rails ruby activerecord

share|improve this question

edited Mar 22 at 21:18

chumakoff

4,31911233

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

> Project.all
=> #<ActiveRecord::Relation []>

> Project.all.class
=> Project::ActiveRecord_Relation

share|improve this question

edited Mar 22 at 21:18

chumakoff

4,31911233

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

share|improve this question

edited Mar 22 at 21:18

chumakoff

4,31911233

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

edited Mar 22 at 21:18

chumakoff

4,31911233

edited Mar 22 at 21:18

chumakoff

4,31911233

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

asked Mar 22 at 19:07

FeifanZFeifanZ

14.8k63875

2 Answers
2

active

oldest

votes

2

There are actually two questions you are asking:

1. How does it work?


2. Why is it like that? (What for?)

@arieljuod has already given you some explanations and a link.

However the second question is still unanswered.

There is another similar question exists which I hope will help you find all the answers:

How can an ActiveRecord::Relation object call class methods

It looks like the two questions (by the link and yours one) answer each other )

Take a look at @nikita-shilnikov's answer. Good luck in your investigation!

share|improve this answer

edited Apr 9 at 10:42

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Very helpful, thank you! I didn't realize it was possible to use class methods as scopes, so didn't think to go down that line of exploration. It seems like being able to support that is the primary motivation behind this pattern.
  
  – FeifanZ
  Mar 23 at 3:05
  

  
  
  
  

add a comment | 

2

Check this line of code from ActiveRecord.

https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/relation/delegation.rb#L23

mangled_name = klass.name.gsub("::", "_")

So, for your questions:

• it get's added on activerecord's base when it extendes the delegation module https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/base.rb#L290




• it's actually the same class, just something like an alias (not actually an alias, it's a constant with the class as value)




• the class is actually an ActiveRecord::Relation, it's just that the name was changed

share|improve this answer

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And all the class methods from Project get mixed into Project::ActiveRecord_Relation, that's how you can say Project.where(...).some_scope and also why you can implement scopes as explicit class methods.
  
  – mu is too short
  Mar 22 at 21:29
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks! I didn't realize class methods were available as scopes; seems like that's the key insight I missed here. I upvoted this answer, but I'm going to give @chumakoff the ✅ because he better addressed the "what for"
  
  – FeifanZ
  Mar 23 at 3:06
  
  

  
  
  
  

add a comment | 

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2

There are actually two questions you are asking:

1. How does it work?


2. Why is it like that? (What for?)

@arieljuod has already given you some explanations and a link.

However the second question is still unanswered.

There is another similar question exists which I hope will help you find all the answers:

How can an ActiveRecord::Relation object call class methods

It looks like the two questions (by the link and yours one) answer each other )

Take a look at @nikita-shilnikov's answer. Good luck in your investigation!

share|improve this answer

edited Apr 9 at 10:42

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Very helpful, thank you! I didn't realize it was possible to use class methods as scopes, so didn't think to go down that line of exploration. It seems like being able to support that is the primary motivation behind this pattern.
  
  – FeifanZ
  Mar 23 at 3:05
  

  
  
  
  

add a comment | 

2

There are actually two questions you are asking:

1. How does it work?


2. Why is it like that? (What for?)

@arieljuod has already given you some explanations and a link.

However the second question is still unanswered.

There is another similar question exists which I hope will help you find all the answers:

How can an ActiveRecord::Relation object call class methods

It looks like the two questions (by the link and yours one) answer each other )

Take a look at @nikita-shilnikov's answer. Good luck in your investigation!

share|improve this answer

edited Apr 9 at 10:42

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Very helpful, thank you! I didn't realize it was possible to use class methods as scopes, so didn't think to go down that line of exploration. It seems like being able to support that is the primary motivation behind this pattern.
  
  – FeifanZ
  Mar 23 at 3:05
  

  
  
  
  

add a comment | 

There are actually two questions you are asking:

1. How does it work?


2. Why is it like that? (What for?)

@arieljuod has already given you some explanations and a link.

However the second question is still unanswered.

There is another similar question exists which I hope will help you find all the answers:

How can an ActiveRecord::Relation object call class methods

It looks like the two questions (by the link and yours one) answer each other )

Take a look at @nikita-shilnikov's answer. Good luck in your investigation!

share|improve this answer

edited Apr 9 at 10:42

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

share|improve this answer

edited Apr 9 at 10:42

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

answered Mar 22 at 21:12

chumakoffchumakoff

4,31911233

2

Check this line of code from ActiveRecord.

https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/relation/delegation.rb#L23

mangled_name = klass.name.gsub("::", "_")

So, for your questions:

• it get's added on activerecord's base when it extendes the delegation module https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/base.rb#L290




• it's actually the same class, just something like an alias (not actually an alias, it's a constant with the class as value)




• the class is actually an ActiveRecord::Relation, it's just that the name was changed

share|improve this answer

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And all the class methods from Project get mixed into Project::ActiveRecord_Relation, that's how you can say Project.where(...).some_scope and also why you can implement scopes as explicit class methods.
  
  – mu is too short
  Mar 22 at 21:29
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks! I didn't realize class methods were available as scopes; seems like that's the key insight I missed here. I upvoted this answer, but I'm going to give @chumakoff the ✅ because he better addressed the "what for"
  
  – FeifanZ
  Mar 23 at 3:06
  
  

  
  
  
  

add a comment | 

2

Check this line of code from ActiveRecord.

https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/relation/delegation.rb#L23

mangled_name = klass.name.gsub("::", "_")

So, for your questions:

• it get's added on activerecord's base when it extendes the delegation module https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/base.rb#L290




• it's actually the same class, just something like an alias (not actually an alias, it's a constant with the class as value)




• the class is actually an ActiveRecord::Relation, it's just that the name was changed

share|improve this answer

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And all the class methods from Project get mixed into Project::ActiveRecord_Relation, that's how you can say Project.where(...).some_scope and also why you can implement scopes as explicit class methods.
  
  – mu is too short
  Mar 22 at 21:29
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks! I didn't realize class methods were available as scopes; seems like that's the key insight I missed here. I upvoted this answer, but I'm going to give @chumakoff the ✅ because he better addressed the "what for"
  
  – FeifanZ
  Mar 23 at 3:06
  
  

  
  
  
  

add a comment | 

Check this line of code from ActiveRecord.

https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/relation/delegation.rb#L23

mangled_name = klass.name.gsub("::", "_")

So, for your questions:

• it get's added on activerecord's base when it extendes the delegation module https://github.com/rails/rails/blob/f40860800c231ecd1daef6cf6b5a8a8eda76478d/activerecord/lib/active_record/base.rb#L290




• it's actually the same class, just something like an alias (not actually an alias, it's a constant with the class as value)




• the class is actually an ActiveRecord::Relation, it's just that the name was changed

share|improve this answer

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222

mangled_name = klass.name.gsub("::", "_")

share|improve this answer

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222

answered Mar 22 at 19:42

arieljuodarieljuod

8,13211222