让 ActiveRecord 查询与左外连接一起工作

Question

我不确定我在语法上做错了什么，希望得到帮助。一个 InventoryItem 有很多 MaintenanceOrders。每个 MaintenanceOrder 都有一个布尔字段 still_usable。从逻辑上讲，我想运行查询仍然可用的所有 InventoryItems，这意味着它们要么根本没有任何 MaintenanceOrders，要么 none MaintenanceOrders 有 still_usable: false 的标志。

快Rspec

describe "test query" do
 before do
   InventoryItem.create(random_id:"a")
   InventoryItem.create(random_id:"b")
   InventoryItem.create(random_id:"c")

   InventoryItem.where(random_id:"a").last.maintenance_orders.create(still_usable:false)
   InventoryItem.where(random_id:"b").last.maintenance_orders.create(still_usable:nil)
   InventoryItem.where(random_id:"b").last.maintenance_orders.create(still_usable:true)


   @query = InventoryItem.left_outer_joins(:maintenance_orders).where.not(maintenance_orders:{still_rentable:false}).distinct
 end
 it "should return b & c" do
   expect(@query.map(&:random_id)).to match_array(["b","c"])
   # a has a maintenance order with flag still_usable:false so is excluded
   # b has maintenance orders, but none have flag still_usable:false, so is included
   # c has no maintenance orders, so is included
 end
end

Answer 1

您可以使用 SQL NOT EXISTS

来实现

InventoryItem.where("NOT EXISTS (
   SELECT * FROM maintenance_orders 
   WHERE (maintenance_orders.inventory_item_id = inventory_items.id) 
   AND maintenance_orders.still_rentable = false)")

让 ActiveRecord 查询与左外连接一起工作

Getting ActiveRecord Query to work with a left outer join

sql

activerecord

ruby-on-rails

rails-activerecord