MongoDB:执行存储的JavaScript函数时出错 [英] MongoDB: Error executing stored JavaScript function

问题描述

在存储的JavaScript函数下面运行时，出现错误:

When I run below stored JavaScript function I get errors:

> db.system.js.save({_id:"last_n_users", value: function(n){return db.users.find().sort({created_at:-1}).limit(n)}})
> db.eval("last_n_users(10)")

以下是错误:

{ "value" : "DBQuery: store.users -> undefined" }

为什么?请帮帮我吗?

推荐答案

find()函数返回一个游标，该游标无法从JavaScript返回. 建议的解决方法是使用toArray()获取数组返回值.

The find() function returns a cursor, which can't be returned from JavaScript. The suggested workaround is to use toArray() to get an array return value.

示例...之前:

> use admin
switched to db admin
> db.system.js.save( { _id : "foo", value: function(n){return db.system.indexes.find().limit(n)} } )         
> db.eval( "foo(3)" )                                                                               
{ "value" : "DBQuery: admin.system.indexes -> undefined" }

正如您所描述的.
之后:

just as you describe.
And after:

> db.system.js.save( { _id : "foo", value: function(n){return db.system.indexes.find().limit(n).toArray()} } )
> db.eval( "foo(3)" )                                                                                         
[
        {
                "name" : "_id_",
                "ns" : "admin.system.users",
                "key" : {
                        "_id" : 1
                }
        },
        {
                "name" : "user_1",
                "ns" : "admin.system.users",
                "key" : {
                        "user" : 1
                },
                "unique" : false
        },
        {
                "name" : "_id_",
                "ns" : "admin.whee",
                "key" : {
                        "_id" : 1
                },
                "v" : 0
        }
]

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