具有空值的MongoDB查询

本文介绍了具有空值的MongoDB查询的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我的收藏集(MongoDB v 2.0.2)具有以下记录:

My collection (MongoDB v 2.0.2) has following records:

dbanization.find({}) { "_id" : 1001, "path" : [ ], "parent" : null } { "_id" : 1002, "path" : [ 1001 ], "parent" : NumberLong(1001) }

organization具有索引:

dbanization.ensureIndex({"path":1}); dbanization.ensureIndex({"parent":1},{sparse:false});

(请注意，我输入了awarnes sparse : false-授予对null进行索引) 但是，执行:

(note I put awarnes sparse : false - to grant that null is indexed) But, executing:

dbanization.find({"parent":null})

返回空集.怎么了?预先谢谢你

Returns empty set. What is wrong? Thank you in advance

推荐答案

我遇到了同样的问题.阅读以下文档后

I had the same issue. After reading the following documents

• 查询和空值
• BSON规范

• querying and nulls
• BSON specification

我尝试查询不同的BSON元素类型，发现我的null表示为BSON元素类型6(未定义，不建议使用)，而不是预期的BSON元素类型10(空).

I tried to query for the different BSON element types and found that my null was represented as a BSON element type 6 (undefined, deprecated) instead of the expected BSON element type 10 (null).

db.collection.find({ field: { "$type" : 6} };