Rails - Mar 2013 - has_many association: building a new association object adds it to the collection ?

Recently I discovered one thing I didn''t even think about, or I
believed it
to work absolutely differently.
So, to explain it, given the following models:

class Project < AR
  has_many :participants
end

class Participant < AR
  belongs_to :project
end

Here is what is going in the console:

irb(main):003:0> p=Project.create(:name=>''java'')
  ←[1m←[36m (0.0ms)←[0m  ←[1mSAVEPOINT active_record_1←[0m
  ←[1m←[35mSQL (43.0ms)←[0m  INSERT INTO "projects"
("created_at", "name",
"updated_at") VALUES (?, ?, ?)  [["
created_at", Thu, 28 Mar 2013 19:27:06 UTC +00:00], ["name",
"java"],
["updated_at", Thu, 28 Mar 2013 19:27:06
 UTC +00:00]]
  ←[1m←[36m (0.0ms)←[0m  ←[1mRELEASE SAVEPOINT active_record_1←[0m
=> #<Project id: 1, name: "java", created_at: "2013-03-28
19:27:06",
updated_at: "2013-03-28 19:27:06">
irb(main):004:0> p.participants
  ←[1m←[35mParticipant Load (0.0ms)←[0m  SELECT "participants".* FROM 
"participants" WHERE "participants"."pro
ject_id" = 1
=> []
irb(main):005:0> part = p.participants.new(username:''toto'')
=> #<Participant id: nil, username: "toto", project_id: 1,
created_at: nil,
updated_at: nil>
irb(main):006:0> p.participants
=> [#<Participant id: nil, username: "toto", project_id: 1,
created_at:
nil, updated_at: nil>]

I always believed that the collection of participants should keep the same 
size (zero in the above case) until I call save on the Project object. As 
you see the collection has been changed by 1, despite the record has not 
been yet save to the database; Is it a normal behaviour ?

Thanks in advance for your help.

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On 28 March 2013 19:35, Serguei Cambour
<s.cambour-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Recently I discovered one thing I didn''t even think about, or I
believed it
> to work absolutely differently.
> So, to explain it, given the following models:
>
> class Project < AR
>   has_many :participants
> end
>
> class Participant < AR
>   belongs_to :project
> end
>
> Here is what is going in the console:
>
> irb(main):003:0> p=Project.create(:name=>''java'')
>   ←[1m←[36m (0.0ms)←[0m  ←[1mSAVEPOINT active_record_1←[0m
>   ←[1m←[35mSQL (43.0ms)←[0m  INSERT INTO "projects"
("created_at", "name",
> "updated_at") VALUES (?, ?, ?)  [["
> created_at", Thu, 28 Mar 2013 19:27:06 UTC +00:00], ["name",
"java"],
> ["updated_at", Thu, 28 Mar 2013 19:27:06
>  UTC +00:00]]
>   ←[1m←[36m (0.0ms)←[0m  ←[1mRELEASE SAVEPOINT active_record_1←[0m
> => #<Project id: 1, name: "java", created_at:
"2013-03-28 19:27:06",
> updated_at: "2013-03-28 19:27:06">
> irb(main):004:0> p.participants
>   ←[1m←[35mParticipant Load (0.0ms)←[0m  SELECT "participants".*
FROM
> "participants" WHERE "participants"."pro
> ject_id" = 1
> => []
> irb(main):005:0> part =
p.participants.new(username:''toto'')
> => #<Participant id: nil, username: "toto", project_id: 1,
created_at: nil,
> updated_at: nil>
> irb(main):006:0> p.participants
> => [#<Participant id: nil, username: "toto", project_id: 1,
created_at: nil,
> updated_at: nil>]
>
> I always believed that the collection of participants should keep the same
> size (zero in the above case) until I call save on the Project object. As
> you see the collection has been changed by 1, despite the record has not
> been yet save to the database; Is it a normal behaviour ?
You have added one to the collection so it appears in the collection
in memory.  Note that there is no need to save the project object in
order to add to its collection as nothing in the project object
changes.  It is the participant that must be saved at some point,
otherwise it will be lost.

Colin

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On 28 Mar 2013, at 21:24, Colin Law
<clanlaw-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote:
> On 28 March 2013 19:35, Serguei Cambour
<s.cambour-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> Recently I discovered one thing I didn''t even think about, or
I believed it
>> to work absolutely differently.
>> So, to explain it, given the following models:
>> 
>> class Project < AR
>>  has_many :participants
>> end
>> 
>> class Participant < AR
>>  belongs_to :project
>> end
>> 
>> Here is what is going in the console:
>> 
>> irb(main):003:0>
p=Project.create(:name=>''java'')
>>  ←[1m←[36m (0.0ms)←[0m  ←[1mSAVEPOINT active_record_1←[0m
>>  ←[1m←[35mSQL (43.0ms)←[0m  INSERT INTO "projects"
("created_at", "name",
>> "updated_at") VALUES (?, ?, ?)  [["
>> created_at", Thu, 28 Mar 2013 19:27:06 UTC +00:00],
["name", "java"],
>> ["updated_at", Thu, 28 Mar 2013 19:27:06
>> UTC +00:00]]
>>  ←[1m←[36m (0.0ms)←[0m  ←[1mRELEASE SAVEPOINT active_record_1←[0m
>> => #<Project id: 1, name: "java", created_at:
"2013-03-28 19:27:06",
>> updated_at: "2013-03-28 19:27:06">
>> irb(main):004:0> p.participants
>>  ←[1m←[35mParticipant Load (0.0ms)←[0m  SELECT
"participants".* FROM
>> "participants" WHERE "participants"."pro
>> ject_id" = 1
>> => []
>> irb(main):005:0> part =
p.participants.new(username:''toto'')
>> => #<Participant id: nil, username: "toto", project_id:
1, created_at: nil,
>> updated_at: nil>
>> irb(main):006:0> p.participants
>> => [#<Participant id: nil, username: "toto",
project_id: 1, created_at: nil,
>> updated_at: nil>]
>> 
>> I always believed that the collection of participants should keep the
same
>> size (zero in the above case) until I call save on the Project object.
As
>> you see the collection has been changed by 1, despite the record has
not
>> been yet save to the database; Is it a normal behaviour ?
> 
> You have added one to the collection so it appears in the collection
> in memory.  Note that there is no need to save the project object in
> order to add to its collection as nothing in the project object
> changes.  It is the participant that must be saved at some point,
> otherwise it will be lost.
Thank you, Colin, for the answer, I believed that every time you call a
collection method, for example:

project.participants

a DB query will be made to get it, but it is not the case.

Regards,


Serguei
> 
> Colin
> 
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