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Ruby 发布时间：2022-04-03 发布网站：大佬教程 code.js-code.com

大佬教程收集整理的这篇文章主要介绍了ruby-on-rails – 如何根据属于第一个模型的另一个模型的属性查询模型？，大佬教程大佬觉得挺不错的，现在分享给大家，也给大家做个参考。

如果我有一个模型人员,其中有多辆车,每辆车可以是汽车或摩托车,我怎样才能查询所有拥有汽车的人和所有拥有摩托车的人？

我不认为这些是正确的：

Person.joins(:vehicles).where(vehicle_type: 'auto')
Person.joins(:vehicles).where(vehicle_type: 'motorcycle')

解决方法

您可以执行以下操作：

Person.includes(:vehicles).where(vehicles: { type: 'auto' })
Person.includes(:vehicles).where(vehicles: { type: 'motorcycle' })

小心.joins和.includes：

# consider these models
Post # table name is posts
  belongs_to :user
                #^^
User # table name is users
  has_many :posts
               #^

# the `includes/joins` methods use the relation name defined in the model:
User.includes(:posts).where(posts: { title: 'Bobby Table' })
                  #^            ^
# but the `where` uses the exact table name:
Post.includes(:user).where(users: { name: 'Bobby' })
                #^^^           ^

一个棘手的问题：

Post
  belongs_to :author,class_name: 'User'
User # table named users
  has_many :posts

Post.includes(:author).where(users: { name: 'John' })
# because table is named users

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