Need help configuring this data model


#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 J.


#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.

    <% @player.outgoing_hits.each do |hit| %>
  • <%=hit.hittee.screen_name%>
  • <%end%>

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

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?


#6

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 J.’
example).