Lets assume i have hundred thousand users
Simple Example,
user = User.where(id: 1..10000)
User Load (30.8ms) SELECT `users`.* FROM `users` WHERE (`users`.`id` BETWEEN 1 AND 10000)
in here, i want to slice more like this,
user.where(id: 100..1000)
User Load (2.9ms) SELECT `users`.* FROM `users` WHERE (`users`.`id` BETWEEN 1 AND 10000) AND (`users`.`id` BETWEEN 100 AND 1000)
Why is active record hitting db twice? it already has result that has bigger data. why does it have to hit db, not just reuse and slice ActiveRecord::Relation?
Is there any good solution for this?
答案 0 :(得分：2)
ActiveRecord keeps track of queries and is able to cache certain duplicate requests, but in this case it's not that immediate for a library to understand that the second one is a subset of the first.
Moreover, there are several reasons why a generic library such as ActiveRecord may not want to implement a caching logic like that one. Caching a large data set in a very large application may result into several Mb of memory, and processes may reach the memory limit of the machine fairly quickly because the garbage collector would not be able to recollect the memory.
Long story short, it's a very bad idea to implement such feature in a generic ORM library.
If you want to implement it in your own code, you are free to do it.
答案 1 :(得分：0)
ActiveRecord is hitting the db twice because you are running it in the console. This invokes the query on each line through .inspect. If this was run within a block of code, invocation would be delayed till you actually access user.
答案 2 :(得分：0)
而不是将两次迭代传递给单个：
User.where（“id介于？和？”之间，100,1000）
它会减少db命中，希望它能回答你的问题