Question

如果我有一个Person模型，has_many Vehicles且每个Vehicle可以是car或motorcycle，那该怎么办？我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')

Answer 1

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

类似问题：

如何根据属于第一个模型的另一个模型的属性查询模型？

1 个答案: