Rails 3:延迟加载与紧急加载

我不确定,但看起来你 belongs_to :serivce Appointment 类和 has_many :appointments Service 上课。对的?

在这种情况下,你的两个例子没有任何区别。在这两种情况下,Rails将执行两个查询:

Appointment Load (0.0ms)  SELECT "appointments".* FROM "appointments" WHERE ("appointments"."id" = 1) LIMIT 1
Service Load (0.0ms)  SELECT "services".* FROM "services" WHERE ("services"."id" = 1) LIMIT 1

s = Service.find(123)

然后做如下事情:

s.appointments.find(1)
s.appointments.find(2)

等等,在代码中的许多地方,对数据库的查询将与这些调用的数量一样多(Rails 3在这里非常聪明,所以如果您执行 s.appointments.each

那样的话最好打电话给:

s = Service.include(:appointments).find(123)

因为那时Rails只执行两个查询:一个用于获取 还有一个去接所有的约会:

Service Load ( 0.0ms )  SELECT "services".* FROM "services" WHERE ("services"."i
d" = 123) LIMIT 1
Appointment Load ( 0.0ms )  SELECT "appointments".* FROM "appointments" WHERE ("
appointments".service_id = 123)