问题
I have a has_many :through association. Players have many Teams and Teams have many Players. The join model, Affiliation, belongs to Players and Teams, and also has a year attribute to keep track of a player's team affiliation (or employment) from year to year.
I can't seem to figure out the right way to build an association based on the following rules:
- Create a new player.
- Associate a team that may be new or existing. So find it or create it, but only create it if the player is saved.
- The association may or may not include a year, but the association should only be created if the player and team are saved.
The Player model looks like:
class Player < ActiveRecord::Base
attr_accessible :name
has_many :affiliations, :dependent => :destroy
has_many :teams, :through => :affiliations
end
The Team model looks like:
class Team < ActiveRecord::Base
attr_accessible :city
has_many :affiliations, :dependent => :destroy
has_many :players, :through => :affiliations
end
The Affiliation model looks like:
class Affiliation < ActiveRecord::Base
attr_accessible :player_id, :team_id, :year
belongs_to :player
belongs_to :team
end
I have been successful at creating the association records without the join model attribute using a create action in the PlayersController that looks like:
class PlayersController < ApplicationController
def create
@player = Player.new(params[:player].except(:teams))
unless params[:player][:teams].blank?
params[:player][:teams].each do |team|
team_to_associate = Team.find_or_initialize_by_id(team[:id], team.except(:year)
@player.teams << team_to_associate
end
end
@player.save
respond_with @player
end
end
After creating a new player with two teams using params like:
{"player"=>{"name"=>"George Baker", "teams"=>[{"city"=>"Buffalo"}, {"city"=>"Detroit"}]}}
the database looks like:
players
id: 1, name: George Baker
teams
id: 1, city: Buffalo
id: 2, city: Seattle
affiliations
id: 1, player_id: 1, team_id: 1, year: null
id: 2, player_id: 1, team_id: 2, year: null
When I try to introduce the year, things fall apart. My most recent attempt at the create action in the PlayersController looks like:
class PlayersController < ApplicationController
def create
@player = Player.new(params[:player].except(:teams))
unless params[:player][:teams].blank?
params[:player][:teams].each do |team|
team_to_associate = Team.find_or_initialize_by_id(team[:id], team.except(:year)
// only additional line...
team_to_associate.affiliations.build({:year => team[:year]})
@player.teams << team_to_associate
end
end
@player.save
respond_with @player
end
end
Now, when creating a new player with two teams using params like:
{"player"=>{"name"=>"Bill Johnson", "teams"=>[{"id"=>"1"}, {"city"=>"Detroit", "year"=>"1999"}]}}
the database looks like:
players
id: 1, name: George Baker
id: 2, name: Bill Johnson
teams
id: 1, city: Buffalo
id: 2, city: Seattle
id: 3, city: Detroit
affiliations
id: 1, player_id: 1, team_id: 1, year: null
id: 2, player_id: 1, team_id: 2, year: null
id: 3, player_id: 2, team_id: 1, year: null
id: 4, player_id: null, team_id: 3, year: 1999
id: 5, player_id: 2, team_id: 3, year: null
So three records were created when only two should have been. The affiliation record id: 3 is correct. For id: 4, the player_id is missing. And for id: 5, the year is missing.
Obviously this is incorrect. Where am I going wrong?
Thanks
回答1:
Edit
Ok, i think i have a better solution. AFAIK, you can't use nested attributes on two levels of depth (though you could test it, maybe it works), but nothing prevents us to simulate this behavior :
class Player < ActiveRecord::Base
has_many :affiliations
has_many :teams, through: :affiliations
accespts_nested_attributes_for :affiliations, allow_destroy: true
end
class Affiliation < ActiveRecord::Base
belongs_to :player
belongs_to :team
validates :player, presence: true
validates :team, presence: true
attr_accessor :team_attributes
before_validation :link_team_for_nested_assignment
def link_team_for_nested_assignment
return true unless team.blank?
self.team = Team.find_or_create_by_id( team_attributes )
end
Now, doing this :
@player = Player.new(
name: 'Bill Johnson',
affiliations_attributes: [
{year: 1999, team_attributes: {id: 1, city: 'Detroit}},
{team_attributes: {city: 'Somewhere else'}}
]
)
@player.save
should create all the required records, and still rollback everything in case of problems (because the save itself is already wrapped in a transaction). As a bonus, all the errors will be associated to @player !
How about this ?
class PlayersController < ApplicationController
def create
ActiveRecord::Base.transaction do
@player = Player.new(params[:player].except(:teams))
raise ActiveRecord::Rollback unless @player.save # first check
unless params[:player][:teams].blank?
@teams = []
params[:player][:teams].each do |team|
team_to_associate = Team.find_or_initialize_by_id(team[:id], team.except(:year))
raise ActiveRecord::Rollback unless team_to_associate.save # second check
if team[:year]
affiliation = team_to_associate.affiliations.build(player: @player, year: team[:year])
raise ActiveRecord::Rollback unless affiliation.save # third check
end
@teams << team_to_associate # keep the object so we have access to errors
end
end
end
flash[:notice] = "ok"
rescue ActiveRecord::Rollback => e
flash[:alert] = "nope"
ensure
respond_with @group
end
end
回答2:
This solution ended up working for me. If anyone uses this code for their own project, however, please know that I haven't tested any other actions besides create. I'm certain some of this will change once I deal with read, update and delete.
class Player < ActiveRecord::Base
attr_accessible :name
has_many :affiliations, :dependent => :destroy
has_many :teams, :through => :affiliations
accepts_nested_attributes_for :affiliations, :allow_destroy => true
attr_accessible :affiliations_attributes
end
class Team < ActiveRecord::Base
attr_accessible :city
has_many :affiliations, :dependent => :destroy
has_many :players, :through => :affiliations
end
class Affiliation < ActiveRecord::Base
attr_accessible :player_id, :team_id, :team_attributes, :year
belongs_to :player
belongs_to :team
accepts_nested_attributes_for :team
def team_attributes=(team_attributes)
self.team = Team.find_by_id(team_attributes[:id])
self.team = Team.new(team_attributes.except(:id)) if self.team.blank?
end
end
class PlayersController < ApplicationController
def create
player_params = params[:player].except(:teams)
affiliation_params = []
unless params[:player][:teams].blank?
params[:player][:teams].each do |team|
affiliation = {}
affiliation[:year] = team[:year] unless team[:year].blank?
affiliation[:team_attributes] = team.except(:year)
affiliation_params << affiliation
end
end
player_params[:affiliation_attributes] = affiliation_params unless affiliation_params.blank?
@player = Player.new(player_params)
@player.save
respond_with @player
end
end
来源：https://stackoverflow.com/questions/13621053/incorrect-database-records-created-for-rails-3-has-many-through-association