如何在MongoDB中实现where条件过滤

其实，我们这些习惯传统关系型数据库开发的人，在过滤数据的时候可能首先想到的是where子句，所以MongoDB中也提供了“$where”。

示例：使用where进行数据查询
> db.emp.find({"$where":"this.age>40"}).pretty();
{
“_id” : ObjectId("599108423268c8e84253be2c"),
“姓名” : “郑琪”,
“性别” : “女”,
“年龄” : 50 ,
“sal” : 4700,
“loc” : “成都”

或者:
> db.emp.find("this.age>40" ).pretty();
{
"_id" : ObjectId("599108423268c8e84253be2c"),
"name" : "郑琪",
"sex" : "女" ,
"age" : 50,
"sal" : 4700,
"loc" : "成都"
}

"$where" 可以可以简化，但这种类型的操作贝尔ongs对每一行的信息进行判断。事实上，它不适合大量数据。使用不方便。其实上面的代码严格来说是一个写操作的函数。

> db.emp.find(function(){return this.age>40;}).pretty();< br/>{
"_id" : ObjectId("599108423268c8e84253be2c"),
"name" : "郑琪",
"sex" : "女",
"年龄" : 50,
"sal" : 4700,
"loc" : "成都"
}

> db.emp.find({"$where" :function(){return this.age>40;}}).pretty();
{
“_id” : ObjectId("599108423268c8e84253be2c"),
“name” : “郑Qi”,
“性别”:“女”,
“年龄”:50,
“sal”:4700,
“loc”:“成都”
}

上面只是一个查询，如果想实现多个条件的判断，那么就需要使用and连接。

> db.emp.find({"$and":[{"$where":"this.age>20"},{"$where":"this.age<25" }]}).pretty();
{
"_id" : ObjectId("599108423268c8e84253be27"),
"name" :"钱二",
"性别" : "女",
"年龄" : 22,
"sal" : 5000,
"loc" : "上海"
}
{
"_id" : ObjectId("599148bd0184ff511bf02b91"),
"姓名" : "林A",
"性别" : "男",
                                                                                                                                                                                                                                            ​ot, " : [
                                                                                                                                                                                                                                                                                 "姓名": "林A的父亲",
                       uot; : 50,
"工作" : "农民"
    },
                                                                     br/> "年龄": 49 ,
            "工作" : "工人"
                                  br/>   ]
}