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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