MongoDB根据内嵌文档的某个键删除数组元素的两种方法介绍

> use test
switched to db test
插入测试数据:
> db.country.insert({"name":"China","province":[{"name":"Henan","code":"1001"},{"name":"Hebei","code":"1002"},{"name":"Jiangsu","code":"1003"}]});
WriteResult({ "nInserted" : 1 })


方法一:
想删除名为"Hebei"的省份信息，分两步:
(1).查找到对应的数组元素，并将其替换为"null"


> db.country.update({"name":"China","province.name":"Hebei"},{"$set":{"province.$":"null"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
此时数组数据如下:
> db.country.find()
{ "_id" : ObjectId("59f97d03a4fe2442400cbd2c"), "name" : "China", "province" : [ { "name" : "Henan", "code" : "1001" }, "null", { "name" : "Jiangsu", "code" : "1003" } ] }


(2).然后再清空数组中的"null"
> db.country.update({"name":"China"},{"$pull":{"province":"null"}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
删除后的最终数据如下:
> db.country.find()
{ "_id" : ObjectId("59f97d03a4fe2442400cbd2c"), "name" : "China", "province" : [ { "name" : "Henan", "code" : "1001" }, { "name" : "Jiangsu", "code" : "1003" } ] }
> 


方法二:
根据某个键直接删除数组元素：
> db.country.update({"name":"China"},{"$pull":{"province":{"name":"Hebei"}}});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> 
> db.country.find()
{ "_id" : ObjectId("59f97e58a4fe2442400cbd2d"), "name" : "China", "province" : [ { "name" : "Henan", "code" : "1001" }, { "name" : "Jiangsu", "code" : "1003" } ] }
> 

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