如何根据属于第一个模型的另一个模型的属性查询模型? [英] How to query a model based on attribute of another model which belongs to the first model?

问题描述

如果我有一个模型 Person，它的 has_many Vehicles 和每个 Vehicle 可以是 car 或 motorcycle，如何查询所有有车的人和所有有摩托车的人?

If I have a model Person, which has_many Vehicles and each Vehicle can be of type car or motorcycle, how can I query for all persons, who have cars and all persons, who have motorcycles?

我不认为这些是正确的:

I don't think these are correct:

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

推荐答案

您可以执行以下操作:

Person.includes(:vehicles).where(vehicles: { vehicle_type: 'auto' })
Person.includes(:vehicles).where(vehicles: { vehicle_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:

---

A tricky one:

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

---

或者，gem activerecord_where_assoc 可以实现这一点(以及更多):

---

Alternatively, the gem activerecord_where_assoc can achieve this (and much more):

Person.where_assoc_exists(:vehicles, vehicle_type: 'auto')

---

类似问题:

• 可能未找到已命名的关联Rails 关联中的拼写错误问题
• Rails 活动记录查询与存在"的关联
• Rails 3, has_one/has_many with拉姆达条件
• Rails 4 范围来查找父母没有孩子
• 加入多个具有活动记录的表
• Rails:查找所有用户其关系具有指定属性

这篇关于如何根据属于第一个模型的另一个模型的属性查询模型?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！