我检查了关于has_many通过关系的 Rails 指南,但他们在视图中的控制器中has_many through 效果的文档很差。
模型:
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,当我使用创建方法时,会自动创建一个 TwitterMembership 对象,但是当我使用新方法然后使用保存方法时,不会创建 TwitterMember。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TwitterMember:
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]]
但是当我在控制器/twitter_accounts_controller中使用new&create做同样的事情时 - 它不是创建TwitterMember:
def new
@twitter_account = @project.twitter_accounts.new
end
def create
@twitter_account = @project.twitter_accounts.new(twitter_account_params)
@twitter_account.save
end
你能解释一下新保存和创建之间的区别吗?如果我像这样直接在我的控制器中使用创建方法可以吗?
def create
@twitter_account = @project.twitter_accounts.create(twitter_account_params)
end
提前谢谢。
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反向关系,以确保关联的build
和new
将一致地设置关系、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
然后应该使这项工作
@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,假设您在发生故障时已经处理了所有边缘情况,则使用 create
是完全可以接受的。例如:如果失败,是否向最终用户显示错误?如果它不应该失败,您应该引发异常(请参阅create!
)以生成某种通知以通知您失败。
为什么
简而言之,如果没有has_many
、has_one
和belongs_to
inverse_of
设置,Rails就不能完全理解将事物粘合在一起的中间模型链。在某些情况下(如create
)Rails会采取"最佳猜测",并且可能会把事情做好。Rails Guide 没有明确说明这一点,但inverse_of的文档对此进行了详细说明。
has_many
、has_one
和belongs_to
关系上设置inverse_of
已经成为Rails的习语,并且应该这样做以确保不需要Rails猜测。