# Confusion about has\_many / belongs\_to **URL:** \ **Category:** Rails\ **Created:** [April 7, 2006, 4:55pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724 "2006-04-07T16:55:05Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![aginghipster](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e9c0ed/32.png) [@aginghipster](https://www.ruby-forum.com/u/aginghipster)\ **Post date:** [April 7, 2006, 4:55pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724/1 "2006-04-07T16:55:05Z")
I have a table called players and its model Player, and I have a table called games and its model Game. In the games table I have: player1\_id int(11) player2\_id int(11) I want the tables to be associated so that I can access the player objects using table.player1 and table.player2 rather than having to lookup the objects based on the ids. I am not sure how to go about this but I suspect I need to use either has\_many or belongs\_to or one of the mixed versions in my Game/Player models. I would be very grateful if someone could shed light on what I need to do here. Thank you Andy ---
**Author:** ![aginghipster](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e9c0ed/32.png) [@aginghipster](https://www.ruby-forum.com/u/aginghipster)\ **Post date:** [April 7, 2006, 5:47pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724/2 "2006-04-07T17:47:05Z")
Well, if a game has more than one player, and your players can take part in more than one game (that’s an assumption, so it could be wrong;), then what you really have is a has\_and\_belongs\_to\_many relationship. That would give you a games\_players join table. In fact, if you wanted to maintain separate player meta data, for each game they participated in, as well as game-specific meta data, you could actually structure this relationship as a has\_many :through. This would probably change the games\_players table into a participants table (or something similar). And you would put: has\_many :games, :through =\> :participants # in the Player model has\_many :players, :through =\> :participants # in the Game model and in the Participant model belongs\_to :game belongs\_to :player -Brian ---
**Author:** ![aginghipster](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e9c0ed/32.png) [@aginghipster](https://www.ruby-forum.com/u/aginghipster)\ **Post date:** [April 7, 2006, 6:07pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724/3 "2006-04-07T18:07:18Z")
A player can only participate in a single game, which should make the situation easy but I can’t quite figure it out… Does the Game model has\_many :player ? Does the Player model belongs\_to :game? and once thats sorted out would I be able to access those associated objects with game.player1 and game.player2 ? That is, does rails know that because games has player1\_id and player2\_id that games.player1 and games.player2 are objects from the players table? You can see I am confused! 😉 -Andy Brian V. Hughes wrote: > Well, if a game has more than one player, and your players can take part > in > more than one game (that’s an assumption, so it could be wrong;), then > what > you really have is a has\_and\_belongs\_to\_many relationship. That would > give you > a games\_players join table. > > In fact, if you wanted to maintain separate player meta data, for each > game > they participated in, as well as game-specific meta data, you could > actually > structure this relationship as a has\_many :through. This would probably > change > the games\_players table into a participants table (or something > similar). And > you would put: > > has\_many :games, :through =\> :participants # in the Player model > has\_many :players, :through =\> :participants # in the Game model > > and in the Participant model > > belongs\_to :game > belongs\_to :player > > -Brian ---
**Author:** ![aginghipster](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e9c0ed/32.png) [@aginghipster](https://www.ruby-forum.com/u/aginghipster)\ **Post date:** [April 7, 2006, 8:07pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724/4 "2006-04-07T20:07:57Z")
On Apr 7, 2006, at 9:07 AM, Andrew C. wrote: > That is, does rails know that because games has player1\_id and > player2\_id that games.player1 and games.player2 are objects from the > players table? > > You can see I am confused! 😉 > > -Andy I believe what you actually need is a has\_one relationship. Although the game does have many players, the way the table is set up, it only has one player1 and one player2. Try this: class Game \< ActiveRecord::Base has\_one :player1, :class\_name =\> ‘Player’ has\_one :player2, :class\_name =\> ‘Player’ end You need to specify the class name because otherwise it will look for a class called Player1 which of course doesn’t exist. You should then be able to use game.player1 or game.player2 to access the players. However, you may find this database design will cause problems later. If, for example, you want to support more than two players, you will need to add more columns for player3, player4, etc. Then what if you want to support, say 16 players. That is a lot of columns and could get messy! If this is at all a possibility, you should go with a true one-to-many relationship. You would do this by putting a game\_id column in the players table and removing the player1 and player2 columns from the games table. You could then use the “has\_many :players” relationship method in your Game model. You can then grab the players with game.players[0] or game.players[1], etc. This also allows you to iterate through all players instead of having to refer to each one individually. Ryan ---
**Author:** ![aginghipster](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e9c0ed/32.png) [@aginghipster](https://www.ruby-forum.com/u/aginghipster)\ **Post date:** [April 7, 2006, 11:29pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724/5 "2006-04-07T23:29:23Z")
On Apr 7, 2006, at 12:40 PM, Andrew C. wrote: > I setup the model as suggested, identically and still have player1\_id > and player2\_id defined the players table, but now it seems > game.player1 > and game.player2 always refer to the same object, sort of like player2 > is an alias of player1. I suspect has\_one is causing this > relationship… Sorry about that, I should have used “belongs\_to” instead of “has\_one” in my last e-mail. I tried this and it works: class Game \< ActiveRecord::Base belongs\_to :player1, :class\_name =\> ‘Player’, :foreign\_key =\> ‘player1\_id’ belongs\_to :player2, :class\_name =\> ‘Player’, :foreign\_key =\> ‘player2\_id’ end The problem was “has\_one” uses the game\_id column in the players table to do the matching. The players.game\_id column is actually unnecessary if you are doing it this way since it will use the player1\_id and player2\_id columns to do the matching. Ryan ---
**Author:** ![aginghipster](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e9c0ed/32.png) [@aginghipster](https://www.ruby-forum.com/u/aginghipster)\ **Post date:** [April 7, 2006, 9:40pm UTC](https://www.ruby-forum.com/t/confusion-about-has-many-belongs-to/93724/6 "2006-04-07T21:40:48Z")
Ryan, I was really hoping your first suggestion would work as it sounded like a great way to implement this being that I have no plans to expand for more players down the road ( its intended for head-to-head only ). I setup the model as suggested, identically and still have player1\_id and player2\_id defined the players table, but now it seems game.player1 and game.player2 always refer to the same object, sort of like player2 is an alias of player1. I suspect has\_one is causing this relationship… However, it appears I already did setup game to have a has\_many relationship with the players table and indeed I can access them via game.players[0] and game.players[1] – I had no idea I could so this is a definite improvement and should prove useful. Thank you very much, its all getting a little clearer to me now. -Andy Ryan B. wrote: > On Apr 7, 2006, at 9:07 AM, Andrew C. wrote: > > > That is, does rails know that because games has player1\_id and > > player2\_id that games.player1 and games.player2 are objects from the > > players table? > > > > You can see I am confused! 😉 > > > > -Andy > > I believe what you actually need is a has\_one relationship. Although > the game does have many players, the way the table is set up, it only > has one player1 and one player2. Try this: > > class Game \< ActiveRecord::Base > has\_one :player1, :class\_name =\> ‘Player’ > has\_one :player2, :class\_name =\> ‘Player’ > end > > You need to specify the class name because otherwise it will look for > a class called Player1 which of course doesn’t exist. You should then > be able to use game.player1 or game.player2 to access the players. > > However, you may find this database design will cause problems later. > If, for example, you want to support more than two players, you will > need to add more columns for player3, player4, etc. Then what if you > want to support, say 16 players. That is a lot of columns and could > get messy! If this is at all a possibility, you should go with a true > one-to-many relationship. > > You would do this by putting a game\_id column in the players table > and removing the player1 and player2 columns from the games table. > You could then use the “has\_many :players” relationship method in > your Game model. You can then grab the players with game.players[0] > or game.players[1], etc. This also allows you to iterate through all > players instead of having to refer to each one individually. > > Ryan