检查MongoDB中的现有文档/嵌入式文档
要检查现有文档/嵌入式文档，请在MongoDB中使用$exists。让我们创建一个包含文档的集合-
> db.demo322.insertOne(
... {'id':1001,
... 'details':[{'Score':10000,Name:"Bob"},
... {'Score':98000,Name:"Sam"}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5113e2f8647eb59e56206c")
}
> db.demo322.insertOne(
... {'id':10002,
... 'details':[{'Score':9000},
... {'Score':91000}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5113faf8647eb59e56206d")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo322.find();
这将产生以下输出-
{
"_id" : ObjectId("5e5113e2f8647eb59e56206c"), "id" : 1001, "details" : [
{ "Score" : 10000, "Name" : "Bob" }, { "Score" : 98000, "Name" : "Sam" }
]
}
{
"_id" : ObjectId("5e5113faf8647eb59e56206d"), "id" : 10002, "details" : [
{ "Score" : 9000 }, { "Score" : 91000 }
]
}以下是检查现有文档/嵌入式文档的查询-
> db.demo322.find({"details.Name":{$exists:true}}).count() > 0;这将产生以下输出-
True