MongoDB将JSON数组字段聚合为其他集合的匹配字段？
为此，创建两个集合并添加一些文档。之后，使用$lookup进行匹配。让我们创建一个包含文档的集合-
> db.demo101.insertOne(
... { "_id" : "1", "Details" : [ { "PId" : "200" }, { "PId" : "201" }, { "PId" : "201" } ] }
... )
{ "acknowledged" : true, "insertedId" : "1" }在find()方法的帮助下显示集合中的所有文档-
> db.demo101.find();
这将产生以下输出-
{ "_id" : "1", "Details" : [ { "PId" : "200" }, { "PId" : "201" }, { "PId" : "201" } ] }以下是使用一些文档创建第二个集合的查询-
> db.demo102.insertOne(
... { "_id" : "201", "CustEmailId" : "Carol@gmail.com" }
... );
{ "acknowledged" : true, "insertedId" : "201" }在find()方法的帮助下显示集合中的所有文档-
> db.demo102.find();
这将产生以下输出-
{ "_id" : "200", "CustEmailId" : "John@gmail.com" }
{ "_id" : "201", "CustEmailId" : "Carol@gmail.com" }以下是为其他集合的匹配字段聚合JSON数组字段的查询-
> db.demo101.aggregate(
... [
... {$unwind:"$Details"},
... {$lookup : {from : "demo102", "localField":"Details.PId", "foreignField":"_id", as :"out"}},
... {$project : {"_id":1, "Details.PId":{$arrayElemAt:["$out.CustEmailId",0]}}},
... {$group:{_id:"$_id", Details : {$push : "$Details"}}}
... ]
... ).pretty()这将产生以下输出-
{
"_id" : "1",
"Details" : [
{
"PId" : "John@gmail.com"
},
{
"PId" : "Carol@gmail.com"
},
{
"PId" : "Carol@gmail.com"
}
]
}