MongoDB聚合组并删除重复的数组值？
为此使用MongoDB聚合，并在其中使用$组。让我们创建一个包含文档的集合-
> db.demo649.insertOne(
... { "_id" : 101, "Names" : [ "John", "Bob", "Bob", "Robert" ], "CountryName" : "US" }
... );
{ "acknowledged" : true, "insertedId" : 101 }
>
> db.demo649.insertOne({ "_id" :102, "Names" : [ "John", "Robert" ], "CountryName" : "UK"});
{ "acknowledged" : true, "insertedId" : 102 }在find()方法的帮助下显示集合中的所有文档-
> db.demo649.find();
这将产生以下输出-
{ "_id" : 101, "Names" : [ "John", "Bob", "Bob", "Robert" ], "CountryName" : "US" }
{ "_id" : 102, "Names" : [ "John", "Robert" ], "CountryName" : "UK" }以下是对聚合组的查询-
> db.demo649.aggregate(
... { $unwind : "$Names"},
... { $group : { _id : "$_id" , Names : { $addToSet : "$Names" } ,
... CountryName : { $first : "$CountryName" }}}
... )这将产生以下输出-
{ "_id" : 102, "Names" : [ "Robert", "John" ], "CountryName" : "UK" }
{ "_id" : 101, "Names" : [ "Robert", "Bob", "John" ], "CountryName" : "US" }