MongoDb-查询数组

问题描述

基于MongoDB文档 https://docs.mongodb.com/manual /tutorial/query-arrays/

Based on the MongoDB documentation https://docs.mongodb.com/manual/tutorial/query-arrays/

我有这个收藏集:

db.inventory.insertMany([
   { item: "journal", qty: 25, tags: ["blank", "red"], dim_cm: [ 14, 21 ] },
   { item: "notebook", qty: 50, tags: ["red", "blank"], dim_cm: [ 14, 21 ] },
   { item: "paper", qty: 100, tags: ["red", "blank", "plain"], dim_cm: [ 14, 21 ] },
   { item: "planner", qty: 75, tags: ["blank", "red"], dim_cm: [ 22.85, 30 ] },
   { item: "postcard", qty: 45, tags: ["blue"], dim_cm: [ 10, 15.25 ] }
]);

这些查询是否等效?

db.inventory.find( { tags: { $all: ["red"] } } )

和

db.inventory.find( { tags: "red" } )

如果它们有不同的用途，什么时候代替另一个使用?

If they have different purposes , when to use one instead of the other?

推荐答案

是的，这两个查询是等效的.您仅在使用 $all 要查询包含多个tags值的文档:

Yes, those two queries are equivalent. You would only use $all when you want to query for the docs containing multiple tags values:

db.inventory.find( { tags: { $all: ["red", "blank"] } } )

此查询将匹配示例集合中除最后一个文档以外的所有文档.

This query would match all but the last document in your example collection.

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