[英]Rails Has Many Through Relationship - Difference Between New-Save and Create
我检查了有关has_many through关系的Rails指南,但是对于has_many through在视图中的控制器中的效果,它们的文档很差。
型号:
class Project < ActiveRecord::Base
has_many :twitter_memberships
has_many :twitter_accounts, through: :twitter_memberships
end
class TwitterAccount < ActiveRecord::Base
has_many :twitter_memberships
has_many :projects, through: :twitter_memberships
end
class TwitterMembership < ActiveRecord::Base
belongs_to :project
belongs_to :twitter_account
end
路线:
resources :projects do
resources :twitter_accounts
end
问题是,当我使用create方法时 ,会自动创建一个TwitterMembership对象,但是当我使用new方法然后再使用save方法时 ,不会创建TwitterMembership。 Stackoverflow中的许多帖子都说create = new&save,但似乎它们并不相同。
例如:
Project.first.twitter_accounts.create(name: "bar")
正在创建TwitterAccount和TwitterMembership:
SQL (0.5ms) INSERT INTO "twitter_accounts" ("created_at", "name", "updated_at") VALUES (?, ?, ?) [["created_at", Thu, 20 Nov 2014 22:01:06 UTC +00:00], ["name", "test_record"], ["updated_at", Thu, 20 Nov 2014 22:01:06 UTC +00:00]]
SQL (0.3ms) INSERT INTO "twitter_memberships" ("created_at", "project_id", "twitter_account_id", "updated_at") VALUES (?, ?, ?, ?) [["created_at", Thu, 20 Nov 2014 22:01:06 UTC +00:00], ["project_id", 1], ["twitter_account_id", 8], ["updated_at", Thu, 20 Nov 2014 22:01:06 UTC +00:00]]
但是,当我使用new&create在controllers / twitter_accounts_controller中执行相同的操作时,它不是在创建TwitterMembership:
def new
@twitter_account = @project.twitter_accounts.new
end
def create
@twitter_account = @project.twitter_accounts.new(twitter_account_params)
@twitter_account.save
end
您能解释一下新保存和创建之间的区别吗? 这样直接在控制器中使用create方法可以吗?
def create
@twitter_account = @project.twitter_accounts.create(twitter_account_params)
end
提前致谢。
编辑。 这是完整的控制器=>
class TwitterAccountsController < ApplicationController
before_action :set_project
before_action :set_twitter_account, only: [:show, :edit, :update, :destroy]
def new
@twitter_account = @project.twitter_accounts.new
end
def create
@twitter_account = @project.twitter_accounts.new(twitter_account_params)
@twitter_account.save
end
private
def set_project
@project = Project.friendly.find(params[:project_id])
end
def set_twitter_account
@twitter_account = TwitterAccount.friendly.find(params[:id])
end
def twitter_account_params
params.require(:twitter_account).permit(:name, :account_id)
end
end
您需要在模型上设置逆向关系,以确保build
和new
的关联将一致地建立关系,外键和中间关联:
class Project < ActiveRecord::Base
has_many :twitter_memberships, inverse_of: :project
has_many :twitter_accounts, through: :twitter_memberships
end
class TwitterMembership < ActiveRecord::Base
belongs_to :project, inverse_of: :twitter_memberships
belongs_to :twitter_account, inverse_of: :twitter_memberships
end
class TwitterAccount < ActiveRecord::Base
has_many :twitter_memberships, inverse_of: :twitter_account
has_many :projects, through: :twitter_memberships
end
那应该使这项工作
@twitter_account = Project.first.twitter_accounts.new(name: 'baz')
@twitter_account.save
瞧:
SQL (0.3ms) INSERT INTO "twitter_accounts" ("created_at", "name", "updated_at") VALUES (?, ?, ?) [["created_at", "2014-11-21 19:19:06.323072"], ["name", "baz"], ["updated_at", "2014-11-21 19:19:06.323072"]]
SQL (0.1ms) INSERT INTO "twitter_memberships" ("created_at", "project_id", "twitter_account_id", "updated_at") VALUES (?, ?, ?, ?) [["created_at", "2014-11-21 19:19:06.324779"], ["project_id", 1], ["twitter_account_id", 7], ["updated_at", "2014-11-21 19:19:06.324779"]]
此外,假设您已经处理了所有发生故障的极端情况,那么使用create
是完全可以接受的。 例如:如果失败,您是否向最终用户显示错误? 如果不应该失败,则应引发异常(请参阅create!
),以生成某种通知以通知您失败。
简而言之,如果没有在has_many
, has_one
和belongs_to
上的inverse_of
设置,Rails不会完全理解将事物粘合在一起的中间模型链。 在某些情况下(例如create
),Rails会做出“最佳猜测”,并可能使事情变得正确。 Rails指南并不清楚,但是有关inverse_of的文档对此进行了说明。
在所有has_many
, has_one
和belongs_to
关系上设置inverse_of
已成为Rails惯用语,应确保不要使用Rails进行猜测。
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