直接在連接模型上保存時validates_uniqueness_of失敗

Question

我有三個模型，Team，Player和TeamMembership。 TeamMembership定義了Team和Player之間的多對多關係。創建新的團隊時，用戶可以獲得11個下拉菜單，每個菜單都包含所有可用的球員。但是，玩家只能擁有一個團隊的成員資格，這正是我想要驗證的。

class Player < ActiveRecord::Base 
    has_many :team_memberships 
    has_many :teams, :through => :team_memberships 
end 

class Team < ActiveRecord::Base 
    has_many :team_memberships 
    has_many :players, :through => :team_memberships 
    accepts_nested_attributes_for :players, :team_memberships 
    validates_associated :team_memberships 
end 

class TeamMembership < ActiveRecord::Base 
    belongs_to :team 
    belongs_to :player 
    validates_uniqueness_of :player_id, scope: :team_id 
end 

# GET /teams/new 
def new 
    @team = Team.new 
    11.times { @team.team_memberships.build } 
end 

<%= f.fields_for :team_memberships do |team_memberships_form| %> 
    <%= team_memberships_form.label :player_id %> 
    <%= team_memberships_form.select(:player_id, options_from_collection_for_select(@Player.available, :id, :name)) %> 
    <br /> 
<% end %> 

當試圖創建一個新的團隊時，以下出現在開發日誌中。 （編輯下降到只有3名球員爲簡潔起見）

Started POST "/teams" for 127.0.0.1 at 2014-02-06 10:48:40 +0100 
Processing by FantasyTeamsController#create as HTML 
    Parameters: {"utf8"=>"✓", "authenticity_token"=>"OwP+nfksvaD0WTQdGjqF5p/shzkiaAodigbFTC6PDD0=", "team"=>{"name"=>"asd", "tournament_id"=>"1", "team_memberships_attributes"=>{"0"=>{"player_id"=>"12"}, "1"=>{"player_id"=>"12"}, "2"=>{"player_id"=>"12"}, "3"=>{"player_id"=>"12"}}}, "commit"=>"Create Fantasy team"} 
    User Load (0.6ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 ORDER BY "users"."id" ASC LIMIT 1 
    Role Exists (0.3ms) SELECT 1 AS one FROM "roles" INNER JOIN "users_roles" ON "roles"."id" = "users_roles"."role_id" WHERE "users_roles"."user_id" = $1 AND "roles"."name" = 'admin' LIMIT 1 [["user_id", 1]](0.3ms) BEGIN 
    FantasyTeamMembership Exists (0.5ms) SELECT 1 AS one FROM "team_memberships" WHERE ("team_memberships"."player_id" = 12 AND "team_memberships"."team_id" IS NULL) LIMIT 1 
    CACHE (0.0ms) SELECT 1 AS one FROM "team_memberships" WHERE ("team_memberships"."player_id" = 12 AND "team_memberships"."team_id" IS NULL) LIMIT 1 
    CACHE (0.0ms) SELECT 1 AS one FROM "team_memberships" WHERE ("team_memberships"."player_id" = 12 AND "team_memberships"."team_id" IS NULL) LIMIT 1 
    CACHE (0.0ms) SELECT 1 AS one FROM "team_memberships" WHERE ("team_memberships"."player_id" = 12 AND "team_memberships"."team_id" IS NULL) LIMIT 1 
    SQL (0.5ms) INSERT INTO "teams" ("created_at", "name", "tournament_id", "updated_at", "user_id") VALUES ($1, $2, $3, $4, $5) RETURNING "id" [["created_at", Thu, 06 Feb 2014 09:48:40 UTC +00:00], ["name", "asd"], ["tournament_id", 1], ["updated_at", Thu, 06 Feb 2014 09:48:40 UTC +00:00], ["user_id", 1]] 
    SQL (0.4ms) INSERT INTO "team_memberships" ("team_id", "player_id") VALUES ($1, $2) RETURNING "id" [["team_id", 8], ["player_id", 12]] 
    SQL (0.3ms) INSERT INTO "team_memberships" ("team_id", "player_id") VALUES ($1, $2) RETURNING "id" [["team_id", 8], ["player_id", 12]] 
    SQL (0.3ms) INSERT INTO "team_memberships" ("team_id", "player_id") VALUES ($1, $2) RETURNING "id" [["team_id", 8], ["player_id", 12]] 
    (14.7ms) COMMIT 
Redirected to http://lolhost:3000/teams/8 
Completed 302 Found in 111ms (ActiveRecord: 34.3ms) 

可以看出，因爲這樣我通過accepts_nested_attributes_for保存的記錄，驗證並不能反映實際的SQL這將運行。

如何獲得我想要的行爲？

Answer 1

通過向Team模型添加自定義驗證方法來解決此問題。

validate :unique_players 

def unique_players 
    player_ids = team_memberships.map { |ft| ft.player_id } 
    if player_ids != player_ids.uniq 
    errors.add(:team_memberships, "must have unique players.") 
    end 
end