在MongoDB中查找键何时未知？
要查找键何时未知，请使用$addField和$objectToArray。首先让我们创建一个包含文档的集合-
> db.demo375.insertOne(
... {
... "details":{
... "Name":"John",
... "Age":23
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5a0ae42ae06a1609a00b06")
}
> db.demo375.insertOne(
... {
... "details":{
... "Name":"David",
... "Age":21
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5a0ae42ae06a1609a00b07")
}
> db.demo375.insertOne(
... {
... "details":{
... "Name":"David",
... "Age":22
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5a0ae42ae06a1609a00b08")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo375.find();
这将产生以下输出-
{ "_id" : ObjectId("5e5a0ae42ae06a1609a00b06"), "details" : { "Name" : "John", "Age" : 23 } }
{ "_id" : ObjectId("5e5a0ae42ae06a1609a00b07"), "details" : { "Name" : "David", "Age" : 21 } }
{ "_id" : ObjectId("5e5a0ae42ae06a1609a00b08"), "details" : { "Name" : "David", "Age" : 22 } }以下是查找键未知的查询-
> db.demo375.aggregate([
... { "$addFields": {
... "UnknownKeys": { "$objectToArray": "$$ROOT" }
... }},
... { "$match": { "UnknownKeys.v.Name": "David" }},
... { "$project": { "UnknownKeys": 0 }}
... ])这将产生以下输出-
{ "_id" : ObjectId("5e5a0ae42ae06a1609a00b07"), "details" : { "Name" : "David", "Age" : 21 } }
{ "_id" : ObjectId("5e5a0ae42ae06a1609a00b08"), "details" : { "Name" : "David", "Age" : 22 } }