Rails 模型同时具有“has_one"和“has_many"，但有一些限制 [英] Rails model that has both 'has_one' and 'has_many' but with some constraints

问题描述

我正在映射 2 个模型:

I am mapping 2 models:

User
Account

class Account 
  has_many :users


class User
  has_one :account

user 表作为其中的 account_id.

The user table as the account_id in it.

现在在帐户模型上，我想创建一个主要用户"，一个帐户只有 1 个折扣.用户表有一个布尔标志:is_primary，我如何在帐户端为具有 is_primary 和 account_id 映射的用户创建一个 has_one.

Now on the Account model I want to create a 'primary user' which an account only has 1 off. The user table has a boolean flag :is_primary, how can I create a has_one on the account side for a user who has the is_primary and account_id mapped.

所以 SQL 看起来像:

So the SQL would look like:

SELECT * FROM users where account_id=123 and is_primary = 1

所以我想要:

用户有一个帐户.一个帐户有很多用户，也有一个主用户.

A user has an account. An account has many users, and has a single primary user also.

推荐答案

方法 1 - 添加新关联

添加一个 has_one 关联与一个 where lambda.这允许您在当前模式中工作.

Add an has_one association with a where lambda. This allows you to work within your current schema.

class Account 
  has_many :users
  has_one  :primary_user, -> { where(is_primary: true) }, :class_name=> "User"
end

现在:

account.users #returns all users associated with the account
account.primary_user #returns the primary user associated with the account
# creates a user with is_primary set to true
account.build_primary_user(name: 'foo bar', email: '[e-mail]')

方法 2 - 添加关联方法

class Account 
  has_many :users do
    def primary
      where(:is_primary => true).first
    end
  end
end

现在:

account.users.primary # returns the primary account

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