set a progressive number.

rubyonrails-talk
1

I want to assign a progressive number to an attribute. I think that I can do this in the model

class Model < ActiveRecord::Base before_validation(:on => :create) do   attribute = Model.count + 1

But there is no method count for Model. I think I'm doing wrong.

2

I want to assign a progressive number to an attribute. I think that I can do this in the model

class Model < ActiveRecord::Base before_validation(:on => :create) do attribute = Model.count + 1

But there is no method count for Model.

Is Model just an example, or did you use that as your model name? There is definitely the count method on this page:

http://ar.rubyonrails.org/classes/ActiveRecord/Calculations/ClassMethods.html#M000292

Walter

3

The real code is:

class FirePrevention < ActiveRecord::Base   default_scope :order => 'practice_number ASC'   before_validation(:on => :create) do     practice_number = self.count + 1   end

It says undefined method count...........

4

I want to assign a progressive number to an attribute. I think that I can do this in the model

class Model < ActiveRecord::Base before_validation(:on => :create) do attribute = Model.count + 1

But there is no method count for Model.

Is Model just an example, or did you use that as your model name?

The real code is:

class FirePrevention < ActiveRecord::Base default_scope :order => 'practice_number ASC' before_validation(:on => :create) do    practice_number = self.count + 1 end

It says undefined method count...........

You may be getting a funny self there, then. Try this instead:

    practice_number = FirePrevention.count + 1

Walter

5

It's the same, same error.

6

But why I must call FirePrevention while I am inside FirePrevention, that's why I use self.

7

I want to assign a progressive number to an attribute. I think that I can do this in the model

class Model < ActiveRecord::Base before_validation(:on => :create) do attribute = Model.count + 1

But there is no method count for Model.

Is Model just an example, or did you use that as your model name?

The real code is:

class FirePrevention < ActiveRecord::Base default_scope :order => 'practice_number ASC' before_validation(:on => :create) do   practice_number = self.count + 1 end

It says undefined method count...........

You may be getting a funny self there, then. Try this instead:

  practice_number = FirePrevention.count + 1

It's the same, same error.

Have you tried this in rails console? In a new blank project, maybe?

Walter

8

I want to assign a progressive number to an attribute. I think that I can do this in the model

class Model < ActiveRecord::Base before_validation(:on => :create) do attribute = Model.count + 1

But there is no method count for Model.

Is Model just an example, or did you use that as your model name?

The real code is:

class FirePrevention < ActiveRecord::Base default_scope :order => 'practice_number ASC' before_validation(:on => :create) do   practice_number = self.count + 1 end

It says undefined method count...........

You may be getting a funny self there, then. Try this instead:

  practice_number = FirePrevention.count + 1

It's the same, same error.

But why I must call FirePrevention while I am inside FirePrevention, that's why I use self.

Well, just to see if self was borked at that point somehow. I recall reading very recently that self could act funny in before filters.

Walter

9

That work if I call FirePrevention.count from a controller.

10

I want to assign a progressive number to an attribute. I think that I can do this in the model

class Model < ActiveRecord::Base before_validation(:on => :create) do attribute = Model.count + 1

But there is no method count for Model.

Is Model just an example, or did you use that as your model name?

The real code is:

class FirePrevention < ActiveRecord::Base default_scope :order => 'practice_number ASC' before_validation(:on => :create) do practice_number = self.count + 1 end

It says undefined method count...........

You may be getting a funny self there, then. Try this instead:

practice_number = FirePrevention.count + 1

It's the same, same error.

Have you tried this in rails console? In a new blank project, maybe?

That work if I call FirePrevention.count from a controller.

That actually makes a ton of sense, since the Model has no notion of the collection of sibling objects, only the Empyrean ideal of the Model that spawned them. But count is a property of a collection of unique objects.

Walter

11

So the undefined method count rised by the model is correct? How about a method to assign a progressive number to FirePrevention.practice_number?

12

Does everyone here realize that the 'id' is typically tied to a database column that is set to auto-increment (in whatever fashion the underlying database supports) for the primary key?

Also, if you ever delete a record, the .count will decrease and you'll get a duplicate for the next created record.

Perhaps you want FirePrevention.max(&:id)+1 if you can't just rely on the id directly.

-Rob

13

Yes, it's apparently mixed into the controller, so you would have to do that there. I could see you adding this to the create method directly, or you could put it in a before_save there, it should work fine. Probably exactly the same code as your initial example.

Walter

14

And even with the above you've got race conditions...

15

You want to use self.class.count.

Self is a reference to the object it's self (in your case, an instance of FirePrevention), self.class is reference to the class.

16

I had not thought about this.

17

I have a multi-tenant system (by subdomain) and each subdomain needs their own perspective on an incrementing check number. This does the job:

  before_validation(:on => :create) do     Check.transaction do       self.number = (Check.maximum(:number) || 0) + 1     end   end

18

But if I use self.maximum(:id) it works, there is no need to use self.class.maximun(:id). Why?