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Star Burger

2007-Mar-06 16:18 UTC

has_many :through

I have the following (simple) scenario in a community project:

There is a simple messaging system where users can send messages to one
or many other users (comparable to email). So a message has one user as
sender and many users as recipients. I''ve modeled it like this:

CREATE TABLE users (
  id INT NOT NULL AUTO_INCREMENT,
  login VARCHAR(80) NOT NULL,
  ...
  primary key (id),
  INDEX (id)
) engine = InnoDB;

create table messages (
    id INT NOT NULL AUTO_INCREMENT,
    user_id int not null,
    subject varchar(255),
    body text,
    primary key(id)
) engine = InnoDB, character set utf8;

create table message_users (
    id INT NOT NULL AUTO_INCREMENT,
    message_id int not null,
    user_id int not null,
    primary key(id)
) engine = InnoDB, character set utf8;

and in Rails:

class Message < ActiveRecord::Base
    belongs_to :user  # sender
    has_many :message_users
    has_many :users, :through => :message_user #recipients
end

class MessageRecipient < ActiveRecord::Base
  belongs_to :message
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :message_users
  has_many :messages, :through => :message_users
end


What I don''t like here is that a message has message.user as sender and
message.users as recipients. I would like to be able to call something
like this:

  message.sender
  message.recipients
  user.messages
  message.recipients << u

Another problem might be that user.messages is not clearly defined in my
code as it could be all messages the user has sent or all messages that
a user has received.

How can I achieve a better solution? Maybe you can help me out...

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Jon Garvin

2007-Mar-06 19:00 UTC

head link

Re: has_many :through

I think this is a strong case for habtm, rather than has_many :through. 
I''m normally a big fan of :through and use it often, but I''ve
come to
realize that sometimes, habtm really is much more appropriate.

First, I''d rename your message_users table to messages_recipients
(note:
both message and recipient are plural), and change the user_id column in
that table to recipient_id.  Then....
(disclaimer: this code is untested, so there may be some typos and other
goofs)

class Message < ActiveRecord::Base
  belongs_to :sender, :class_name => ''User''
  has_and_belongs_to_many :recipients, :class_name =>
''User''
end


class User < ActiveRecord::Base
  has_many :sent_messages, :class_name => ''Message''
  has_and_belongs_to_many :received_messages, :class_name =>
''Message''
end


now...
@user.sent_messages
@user.received_messages
@message.sender
@message.recipients

voila!

get rid of your MessageRecipient class.  You don''t need it.

Star Burger wrote:> I have the following (simple) scenario in a community project:
>
> There is a simple messaging system where users can send messages to one
> or many other users (comparable to email). So a message has one user as
> sender and many users as recipients. I''ve modeled it like this:
>
> CREATE TABLE users (
>   id INT NOT NULL AUTO_INCREMENT,
>   login VARCHAR(80) NOT NULL,
>   ...
>   primary key (id),
>   INDEX (id)
> ) engine = InnoDB;
>
> create table messages (
>     id INT NOT NULL AUTO_INCREMENT,
>     user_id int not null,
>     subject varchar(255),
>     body text,
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> create table message_users (
>     id INT NOT NULL AUTO_INCREMENT,
>     message_id int not null,
>     user_id int not null,
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> and in Rails:
>
> class Message < ActiveRecord::Base
>     belongs_to :user  # sender
>     has_many :message_users
>     has_many :users, :through => :message_user #recipients
> end
>
> class MessageRecipient < ActiveRecord::Base
>   belongs_to :message
>   belongs_to :user
> end
>
> class User < ActiveRecord::Base
>   has_many :message_users
>   has_many :messages, :through => :message_users
> end
>
>
> What I don''t like here is that a message has message.user as
sender and
> message.users as recipients. I would like to be able to call something
> like this:
>
>   message.sender
>   message.recipients
>   user.messages
>   message.recipients << u
>
> Another problem might be that user.messages is not clearly defined in my
> code as it could be all messages the user has sent or all messages that
> a user has received.
>
> How can I achieve a better solution? Maybe you can help me out...
>
>   

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Jon Garvin

2007-Mar-06 19:05 UTC

head link

Re: has_many :through

Whoops, I knew I''d forget something... change this line in the User
class to add the foreign_key.

has_and_belongs_to_many :received_messages, :class_name =>
''Message'',
:foreign_key => :recipient_id

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Michael Kovacs

2007-Mar-06 23:54 UTC

head link

Re: has_many :through

I''m wondering why the has_many :through? Your join model has no extra  
attributes at all. Why not just

Message
   belongs_to :sender
   has_and_belongs_to_many :recipients

User
   has_many :sent_messages, :class_name => ''Message''
   has_and_belongs_to_many :received_messages, :class_name =>
''Message''

This gives you all the scenarios you desired and appears to be much  
simpler than the path you are currently going down. I''d love to hear  
other options using has_many :through with more attributes on the  
join model.

-Michael
http://javathehutt.blogspot.com

On Mar 6, 2007, at 8:18 AM, Star Burger wrote:
>
> I have the following (simple) scenario in a community project:
>
> There is a simple messaging system where users can send messages to  
> one
> or many other users (comparable to email). So a message has one  
> user as
> sender and many users as recipients. I''ve modeled it like this:
>
> CREATE TABLE users (
>   id INT NOT NULL AUTO_INCREMENT,
>   login VARCHAR(80) NOT NULL,
>   ...
>   primary key (id),
>   INDEX (id)
> ) engine = InnoDB;
>
> create table messages (
>     id INT NOT NULL AUTO_INCREMENT,
>     user_id int not null,
>     subject varchar(255),
>     body text,
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> create table message_users (
>     id INT NOT NULL AUTO_INCREMENT,
>     message_id int not null,
>     user_id int not null,
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> and in Rails:
>
> class Message < ActiveRecord::Base
>     belongs_to :user  # sender
>     has_many :message_users
>     has_many :users, :through => :message_user #recipients
> end
>
> class MessageRecipient < ActiveRecord::Base
>   belongs_to :message
>   belongs_to :user
> end
>
> class User < ActiveRecord::Base
>   has_many :message_users
>   has_many :messages, :through => :message_users
> end
>
>
> What I don''t like here is that a message has message.user as
sender
> and
> message.users as recipients. I would like to be able to call something
> like this:
>
>   message.sender
>   message.recipients
>   user.messages
>   message.recipients << u
>
> Another problem might be that user.messages is not clearly defined  
> in my
> code as it could be all messages the user has sent or all messages  
> that
> a user has received.
>
> How can I achieve a better solution? Maybe you can help me out...
>
> -- 
> Posted via http://www.ruby-forum.com/.
>
> >

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Star Burger

2007-Mar-07 12:16 UTC

head link

Re: has_many :through

Jon Garvin wrote:> Whoops, I knew I''d forget something... change this line in the
User
> class to add the foreign_key.
> 
> has_and_belongs_to_many :received_messages, :class_name =>
''Message'',
> :foreign_key => :recipient_id
Hmmm. That didn''t work for me. user.received_messages caused a look for
table messages_users which is not there.

Star

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Thorsten

2007-Mar-07 12:26 UTC

head link

Re: has_many :through

has_and_belongs_to_many automatically assumes that the join table for
the association is named like this.

tablename1_tablename2

where tablename1 is the table that comes first alphabetically. So for
a has_anf_belong_to_many association, you have to rename your
message_users table to messages_users, OR:

has_and_belongs_to_many received_messages, :class_name =>
''Message'', :foreign_key => :recipient_id, :join_table =>
"message_users"


On 7 Mrz., 13:16, Star Burger
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> Jon Garvin wrote:
> > Whoops, I knew I''d forget something... change this line in
the User
> > class to add the foreign_key.
>
> > has_and_belongs_to_many :received_messages, :class_name =>
''Message'',
> > :foreign_key => :recipient_id
>
> Hmmm. That didn''t work for me. user.received_messages caused a
look for
> table messages_users which is not there.
>
> Star
>
> --
> Posted viahttp://www.ruby-forum.com/.

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Star Burger

2007-Mar-07 12:58 UTC

head link

Re: has_many :through

Star Burger wrote:> Jon Garvin wrote:
>> Whoops, I knew I''d forget something... change this line in the
User
>> class to add the foreign_key.
>> 
>> has_and_belongs_to_many :received_messages, :class_name =>
''Message'',
>> :foreign_key => :recipient_id
> 
> Hmmm. That didn''t work for me. user.received_messages caused a
look for
> table messages_users which is not there.
> 
> Star
The following ist working via habtm:

create table messages_users (
    message_id int not null,
    user_id int not null,

    primary key(message_id, user_id)
) engine = InnoDB, character set utf8;

class Message < ActiveRecord::Base
  belongs_to :sender, :class_name => ''User''
  has_and_belongs_to_many :recipients, :class_name =>
''User'',
:foreign_key => ''message_id''
end

class User < ActiveRecord::Base
  has_many :sent_messages, :class_name => ''Message''
  has_and_belongs_to_many :received_messages, :class_name =>
''Message'',
:foreign_key => :user_id
end

Puuuh. Thanks for your advice.

-- 
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Conrad Taylor

2007-Mar-07 16:08 UTC

head link

Re: has_many :through

Hi Star, you should be able to do things that you need to do.  The
:through allows you to have alot more flexibility in my opinion in the
event that you need to add additional field(s) to the join model.
Thus, you should be able to do the following with your current models:

message.user
message.message_users
message.users
message.users << user1
user.message_users
user.messages
user.messages << message1

Please revisit the AWDwRv2 for complete list of dynamically generated
methods using :through.

Good luck,

-Conrad

On 3/6/07, Star Burger
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> I have the following (simple) scenario in a community project:
>
> There is a simple messaging system where users can send messages to one
> or many other users (comparable to email). So a message has one user as
> sender and many users as recipients. I''ve modeled it like this:
>
> CREATE TABLE users (
>   id INT NOT NULL AUTO_INCREMENT,
>   login VARCHAR(80) NOT NULL,
>   ...
>   primary key (id),
>   INDEX (id)
> ) engine = InnoDB;
>
> create table messages (
>     id INT NOT NULL AUTO_INCREMENT,
>     user_id int not null,
>     subject varchar(255),
>     body text,
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> create table message_users (
>     id INT NOT NULL AUTO_INCREMENT,
>     message_id int not null,
>     user_id int not null,
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> and in Rails:
>
> class Message < ActiveRecord::Base
>     belongs_to :user  # sender
>     has_many :message_users
>     has_many :users, :through => :message_user #recipients
> end
>
> class MessageRecipient < ActiveRecord::Base
>   belongs_to :message
>   belongs_to :user
> end
>
> class User < ActiveRecord::Base
>   has_many :message_users
>   has_many :messages, :through => :message_users
> end
>
>
> What I don''t like here is that a message has message.user as
sender and
> message.users as recipients. I would like to be able to call something
> like this:
>
>   message.sender
>   message.recipients
>   user.messages
>   message.recipients << u
>
> Another problem might be that user.messages is not clearly defined in my
> code as it could be all messages the user has sent or all messages that
> a user has received.
>
> How can I achieve a better solution? Maybe you can help me out...
>
> --
> Posted via http://www.ruby-forum.com/.
>
> >
>
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Michael Kovacs

2007-Mar-08 02:07 UTC

head link

Re: has_many :through

Hey Conrad, list...

So while it''s true that using has_many :through does give you that  
flexibility the fact that you now need to find a model for that join  
table adds extra complexity to your domain model that you wouldn''t  
otherwise have with a standard habtm relationship. But your point is  
well taken. If you think it''s quite possible for your join table to  
have additional attributes in the future making it a  
has_many :through from the start saves you the pain of a data  
migration later. But doing so as a manner of standard practice seems  
to be overkill IMHO.

Best,

-Michael
http://javathehutt.blogspot.com

On Mar 7, 2007, at 8:08 AM, Conrad Taylor wrote:
>
> Hi Star, you should be able to do things that you need to do.  The
> :through allows you to have alot more flexibility in my opinion in the
> event that you need to add additional field(s) to the join model.
> Thus, you should be able to do the following with your current models:
>
> message.user
> message.message_users
> message.users
> message.users << user1
> user.message_users
> user.messages
> user.messages << message1
>
> Please revisit the AWDwRv2 for complete list of dynamically generated
> methods using :through.
>
> Good luck,
>
> -Conrad
>
> On 3/6/07, Star Burger
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>>
>> I have the following (simple) scenario in a community project:
>>
>> There is a simple messaging system where users can send messages  
>> to one
>> or many other users (comparable to email). So a message has one  
>> user as
>> sender and many users as recipients. I''ve modeled it like
this:
>>
>> CREATE TABLE users (
>>   id INT NOT NULL AUTO_INCREMENT,
>>   login VARCHAR(80) NOT NULL,
>>   ...
>>   primary key (id),
>>   INDEX (id)
>> ) engine = InnoDB;
>>
>> create table messages (
>>     id INT NOT NULL AUTO_INCREMENT,
>>     user_id int not null,
>>     subject varchar(255),
>>     body text,
>>     primary key(id)
>> ) engine = InnoDB, character set utf8;
>>
>> create table message_users (
>>     id INT NOT NULL AUTO_INCREMENT,
>>     message_id int not null,
>>     user_id int not null,
>>     primary key(id)
>> ) engine = InnoDB, character set utf8;
>>
>> and in Rails:
>>
>> class Message < ActiveRecord::Base
>>     belongs_to :user  # sender
>>     has_many :message_users
>>     has_many :users, :through => :message_user #recipients
>> end
>>
>> class MessageRecipient < ActiveRecord::Base
>>   belongs_to :message
>>   belongs_to :user
>> end
>>
>> class User < ActiveRecord::Base
>>   has_many :message_users
>>   has_many :messages, :through => :message_users
>> end
>>
>>
>> What I don''t like here is that a message has message.user as  
>> sender and
>> message.users as recipients. I would like to be able to call  
>> something
>> like this:
>>
>>   message.sender
>>   message.recipients
>>   user.messages
>>   message.recipients << u
>>
>> Another problem might be that user.messages is not clearly defined  
>> in my
>> code as it could be all messages the user has sent or all messages  
>> that
>> a user has received.
>>
>> How can I achieve a better solution? Maybe you can help me out...
>>
>> --
>> Posted via http://www.ruby-forum.com/.
>>
>>>
>>
>
> >

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Star Burger

2007-Mar-08 13:26 UTC

head link

Re: has_many :through

I''ve implemented

class Message < ActiveRecord::Base
  belongs_to :sender, :class_name => ''User''
  has_and_belongs_to_many :recipients, :class_name =>
''User''
end

class User < ActiveRecord::Base
  has_many :sent_messages, :class_name => ''Message''
  has_and_belongs_to_many :received_messages, :class_name =>
''Message''
end

with

CREATE TABLE users (
  id INT NOT NULL AUTO_INCREMENT,
  login VARCHAR(80) NOT NULL,
  ...
  primary key (id),
  INDEX (id)
) engine = InnoDB;

create table messages (
    id INT NOT NULL AUTO_INCREMENT,
    user_id int not null,
    subject varchar(255),
    body text,
    created_at DATETIME default NULL,
    modified_at DATETIME default NULL,

    primary key(id)
) engine = InnoDB, character set utf8;

create table messages_users (
    message_id int not null,
    user_id int not null,

    primary key(message_id, user_id)
) engine = InnoDB, character set utf8;

First everything seemed fine. But user.received_messages delivers 
message objects that are DEFINITELY NOT in the database (wrong sender 
ID)!! I had only one singel message in the DB, but

user.received_messages.first yields another object than Message.find 
:first

Strange, strange!!! A bug maybe?

-- 
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Michael Kovacs

2007-Mar-08 17:42 UTC

head link

Re: has_many :through

Your tables and classes look correct to me. Assuming that you are  
creating your messages properly by adding the correct sender and  
recipients your data should be returned correctly when you access  
those relations. Write a unit test and see what is in the DB after  
you send a single message so you can be sure things are behaving as  
you suspect.

-Michael
http://javathehutt.blogspot.com

On Mar 8, 2007, at 5:26 AM, Star Burger wrote:
>
> I''ve implemented
>
> class Message < ActiveRecord::Base
>   belongs_to :sender, :class_name => ''User''
>   has_and_belongs_to_many :recipients, :class_name =>
''User''
> end
>
> class User < ActiveRecord::Base
>   has_many :sent_messages, :class_name => ''Message''
>   has_and_belongs_to_many :received_messages, :class_name =>
''Message''
> end
>
> with
>
> CREATE TABLE users (
>   id INT NOT NULL AUTO_INCREMENT,
>   login VARCHAR(80) NOT NULL,
>   ...
>   primary key (id),
>   INDEX (id)
> ) engine = InnoDB;
>
> create table messages (
>     id INT NOT NULL AUTO_INCREMENT,
>     user_id int not null,
>     subject varchar(255),
>     body text,
>     created_at DATETIME default NULL,
>     modified_at DATETIME default NULL,
>
>     primary key(id)
> ) engine = InnoDB, character set utf8;
>
> create table messages_users (
>     message_id int not null,
>     user_id int not null,
>
>     primary key(message_id, user_id)
> ) engine = InnoDB, character set utf8;
>
> First everything seemed fine. But user.received_messages delivers
> message objects that are DEFINITELY NOT in the database (wrong sender
> ID)!! I had only one singel message in the DB, but
>
> user.received_messages.first yields another object than Message.find
> :first
>
> Strange, strange!!! A bug maybe?
>
> -- 
> Posted via http://www.ruby-forum.com/.
>
> >

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Rails - Mar 2007 - has_many :through

has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through

Re: has_many :through