活动记录多个选择

什么的ActiveRecord做我写来实现这一目标：活动记录多个选择

SELECT COUNT(*), SUM(`users`.`sign_in_count`), MAX(`users`.`sign_in_count`) FROM `users` WHERE (`users`.`some_field` = 'some_condition')

我怀疑语法是隐约像：

User.where(some_field: some_condition).count.and.sum(:sign_in_count).and.maximum(:sign_in_count)

目前有这样的：

:001:0> User.where(some_field: some_condition).count 
    (1ms) SELECT COUNT(*) FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> 10 
:002:0> User.where(some_field: some_condition).sum(:sign_in_count) 
    (1ms) SELECT SUM(`users`.`sign_in_count`) FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> 100 
:003:0> User.where(some_field: some_condition).maximum(:sign_in_count) 
    (1ms) SELECT MAX(`users`.`sign_in_count`) FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> 50

ActiveRecord是否能够在一个查询中进行多个选择？我的真实世界用例有点重，并且有多个条件，所以过滤后值得抓取所有结果。我想我能做：

:004:0> all_things = User.select(:sign_in_count).where(some_field: some_condition)

但仍然会做一个呼叫每次当它被称为时间：

:005:0> all_things.count 
    (1ms) SELECT COUNT(*) FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> 10 
:006:0> all_things.sum(:sign_in_count) 
    (1ms) SELECT SUM(`users`.`sign_in_count`) FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> 100 
:007:0> all_things.maximum(:sign_in_count) 
    (1ms) SELECT MAX(`users`.`sign_in_count`) FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> 50

所以我可以做.to_a并被迫使用更少的优雅方法

:008:0> all_things = User.select(:sign_in_count).where(some_field: some_condition).to_a 
    User Load (0.9ms) SELECT `users`.`sign_in_count` FROM `users` WHERE (`users`.`some_field` = 'some_condition') 
=> [#<User id: nil, sign_in_count: 0>, ... many elements 
:009:0> all_things.count 
=> 10 
:010:0> all_things.inject(0){|r,e| r+e.sign_in_count} 
=> 100 
:011:0> all_things.inject(0){|r,e| [r,e.sign_in_count].max} 
=> 50

必须有一个漂亮的方式......这不会迫使我填补毫厘行纳秒到内存中，而不是几个结果，或做到这一点：

:012:0> count, sum, max = ActiveRecord::Base.connection.execute("SELECT COUNT(*), SUM(`users`.`sign_in_count`), MAX(`users`.`sign_in_count`) FROM `users` WHERE (`users`.`some_field` = 'some_condition')").to_a.first

来源

2017-06-16 xxjjnn

使用select：

stats = User.select("count(*) as num_users", "sum(sign_in_count) as total_sign_ins", "max(sign_in_count) as max_sign_ins") 
      .where(age: 18).first

然后你就可以访问这些像这样：

stats.num_users 
stats.total_sign_ins 
stats.max_sign_ins

来源

2017-06-16 13:14:41 jimworm

活动记录多个选择

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