Rails ActiveRecord Association問題

Question

我有2個模型：

Performance和PerformanceType以及2個相應的表格：performance和performance_types。

表演中有一個外鍵列「performance_type_id」。

如何使用ActiveRecord關聯從另一個表中獲取performance_type_id的名稱？

class Performance < ActiveRecord::Base 
has_one :users 
has_one :rates 
has_one :performace_types 
end 

class PerformanceType < ActiveRecord::Base 
    belongs_to :performances 
end 

有了上面的代碼我嘗試做的到控制檯：

myvar = Performance.first 
myvar.performance_types 
NoMethodError: undefined method `performance_types' for #<Performance:0x007f9694b3e700> 

我知道這個問題是我的活動記錄協會的不好解釋，誰能幫助我？

關於。

從創建到外鍵添加遷移...

class CreatePerformances < ActiveRecord::Migration 
    def change 
    create_table :performances do |t| 

     t.timestamps null: false 
    end 
    end 
end 

class CreatePerformanceTypes < ActiveRecord::Migration 
    def change 
    create_table :performance_types do |t| 

     t.timestamps null: false 
    end 
    end 
end 

class AddPerformanceTypeIdToPerformance < ActiveRecord::Migration 
    def change 
    add_column :performances, :performance_type_id, :integer 
    end 
end 

class AddAppointmentInfoToPerformance < ActiveRecord::Migration 
    def change 
    add_column :performances, :user_id, :integer 
    add_column :performances, :start_at, :datetime 
    add_column :performances, :end_at, :datetime 
    end 
end 

class AddUserToPerformances < ActiveRecord::Migration 
    def change 
    add_foreign_key :performances, :users 
    end 
end 

class AddTypeToPerformances < ActiveRecord::Migration 
    def change 
    add_foreign_key :performances, :performance_types 
    end 
end 

class AddAdditionalFieldsToPerformanceType < ActiveRecord::Migration 
    def change 
    add_column :performance_types, :name, :string 
    add_column :performance_types, :description, :string 
    end 
end 

class AddPerformanceTypeToRate < ActiveRecord::Migration 
    def change 
    add_foreign_key :rates, :performance_types 
    end 
end 

class AddRateToPerformances < ActiveRecord::Migration 
    def change 
    add_column :performances, :rate_id, :integer 
    add_foreign_key :performances, :rates 
    end 
end 

Answer 1

我認爲這是你想要的。外鍵performance_type_id保持在演奏中。您有許多演出類型相同的演出，但每種演出只有一種演出類型。

class Performance < ActiveRecord::Base 
    # note performance type is singular 
    belongs_to :performance_type 
end 

class PerformanceType < ActiveRecord::Base 
    has_many :performances 
end 

p = Performance.first 
# this should work 
p.performance_type 

Answer 2

has_one和belongs_to指單個對象，所以你應該使用的單一化的形式

class Performance < ActiveRecord::Base 
    has_one :users 
    has_one :rates 
    has_one :performance_type 
end 

class PerformanceType < ActiveRecord::Base 
    belongs_to :performance 
end 

Answer 3

你應該改變你的表演類上市與單數模型（不是複數）的「has_one」關係：

class Performance < ActiveRecord::Base 
    has_one :user 
    has_one :rate 
    has_one :performance_type 
end 

class PerformanceType < ActiveRecord::Base 
    belongs_to :performance 
end 

同樣重要的是，你的遷移文件的配置是否正確，太：

class CreatePerformances < ActiveRecord::Migration 
    def change 
    create_table :performances do |t| 
    end 

    create_table :performance_types do |t| 
     t.belongs_to :performance, index: true 
     t.belongs_to :rate 
     t.belongs_to :user 
    end 
    end 
end