Need help configuring this data model

rubyonrails-talk
1

Consider 2 tables: Player-> column player_id and Hit-> columns player_id, hit_player_id

I want one model for Player and one model for a Hit. Any player has many hits against another player. So from a Player I want to be able to get all the Hits, and from the Hit get the hit Player. On the other hand, from a Player I want to retrieve all Hits against that player (were player_id = hits.hit_player_id) and the player_id from that hit.

So far I have:

class Player < ActiveRecord::Base     has_many :hits end

and

class Hit < ActiveRecord::Base     belongs_to :player end

But I can't figure out how to map the 'hit' player.

Thanks for the help!

2

A quick note first - Player most likely shouldn't have a player_id column - the Rails convention is to simply call it id.

What you're looking for are some of the options to has_many:

class Player < ActiveRecord::Base   has_many :outgoing_hits, :class_name => 'Hit', :foreign_key => 'hitter_id'   has_many :incoming_hits, :class_name => 'Hit', :foreign_key => 'hittee_id'

  has_many :hittees, :through => :outgoing_hits   has_many :hitters, :through => :incoming_hits end

class Hit < ActiveRecord::Base   belongs_to :hitter, :class_name => 'Player'   belongs_to :hittee, :class_name => 'Player' end

Given a Player object, this is what you can do:

player.outgoing_hits # => list of hits by the player player.incoming_hits # => list of hits to the player player.hittees # => list of all players hit by this player player.hitters # => list of all players hitting this player

You can switch the names around, but that's the idea.

--Matt Jones

3

Thanks very much, I will give that a try. Yes I did have the column for player_id as "id", I mis-typed that, but its a good reminder, appreciated.

-Brad

4

This approach doesn't seem to be working for me.

I've set up the models as described above. class Player < ActiveRecord::Base   has_many :outgoing_hits, :class_name => 'Hit', :foreign_key => 'player_id'   has_many :incoming_hits, :class_name => 'Hit', :foreign_key => 'hit_player_id'

  has_many :hittees, :through => :outgoing_hits   has_many :hitters, :through => :incoming_hits end

class Tag < ActiveRecord::Base   belongs_to :hitter, :class_name => 'Player'   belongs_to :hittee, :class_name => 'Player' end

For player foo, I'm trying to list all the name of all players hit. <ul> <% @player.outgoing_hits.each do |hit| %> <li><%=hit.hittee.screen_name%></li> <%end%> </ul>

But, "hittee" is null, although I can access other properties of the hit.

You have a nil object when you didn't expect it! The error occurred while evaluating nil.screen_name

Here's the key columns of the 2 tables involved: Player{ id:integer screen_name:varchar }

Hit{   id:integer   player_id:integer   hit_player_id:integer }

5

Your associations and table columns don't match. You have to tell Rails how to map hitter and hittee if you are not following convention. By default foreign key for a belongs_to association is the name of the association with an "_id" suffix.

So if you want to follow convention, you change Hit-table to be like this:

Hit {    id:integer    hitter_id:integer    hittee_id:integer }

and change Player-class to use those column names (like in Matt Jones' example).

6

Correcting the column names did the trick. Is there a similar mechanism to the foreign-key hnit that can be used? I thought there used to be an identified-by keyword?