Question

这是一个多问题

从猫鼬的结果中，我可以通过result.length获得结果中的几项。

我如何获得特定物品，例如

Person.find({'exployment.office':'Greenway'})
        .exec(function(err, result){
            //from the result, how can i get those items with
            result.length would give me the number of items in the result
            but how can i get a specific item without having to use loop to get 
            the specific item within the result
            //There are like fifty people in the result,
            //how can i get the number of items in result
        });

在SQL中，我有这样的查询

select * 
from table1, table2 
where table2.field2 = value1 
  and table2.field2 = table1.field2
  and table1.value1 = value3

例如

select * 
from city, state 
where state.name = 'xxy' 
  and state.id = city.state_id
  and city.name != 'yyy'

如何将其转换为猫鼬？

在SQL中，如果我想选择名字例如为史密斯，女王，我可以使用类似的东西

select * 
from table 
where first_name in (Smith, Queen)

这将为我的名字与SMith和Queen相匹配的人提供结果

如何用猫鼬做到这一点？

Answer 1

select * 
from Person 
where first_name in (Smith, Queen)

使用$in可以简单地做到这一点：

Person.find({'first_name': { $in: ['Smith', 'Queen']}}) ...

下一个：

select * 
from city, state 
where state.name = 'xxy' 
  and state.id = city.state_id
  and city.name != 'yyy'

使用猫鼬，您将需要使用populate并创建具有ref关系的架构。

City.find({ "name": { $ne: "yyy"} }).populate({
    "path": "state",
    "match": { "state.name": "xxy" }
}) ...

下一个：

Person.find({'exployment.office':'Greenway'})
        .exec(function(err, result){
            //from the result, how can i get those items with
            result.length would give me the number of items in the result
            but how can i get a specific item without having to use loop to get 
            the specific item within the result
            //There are like fifty people in the result,
            //how can i get the number of items in result
        });

在exec查询之前，您将尽可能多地进行过滤以获取所需的记录，而不是在获得所有结果之后进行过滤。 result.length肯定会给您计数，尽管您可以通过类似方法获得计数；

 Person.count({first_name: "Smith"}).exec() ...

猫鼬和SQL比较

1 个答案: