Kiểm tra document đã tồn tại trong MongoDB?

Sử dụng findOne() với cú pháp:

db.yourCollectionName.findOne({yourFieldName: 'yourValue'});

Tạo collection:

> db.checkExistingDemo.insertOne({"StudentName":"John"});
{ "acknowledged" : true, "insertedId" : ObjectId("5cbdf90dac184d684e3fa265") }
> db.checkExistingDemo.insertOne({"StudentName":"Carol"});
{ "acknowledged" : true, "insertedId" : ObjectId("5cbdf912ac184d684e3fa266") }
> db.checkExistingDemo.insertOne({"StudentName":"Sam"});
{ "acknowledged" : true, "insertedId" : ObjectId("5cbdf916ac184d684e3fa267") }
> db.checkExistingDemo.insertOne({"StudentName":"Mike"});
{ "acknowledged" : true, "insertedId" : ObjectId("5cbdf91bac184d684e3fa268") }

Hiển thị tất cả:

> db.checkExistingDemo.find().pretty();

Kết quả:

{ "_id" : ObjectId("5cbdf90dac184d684e3fa265"), "StudentName" : "John" }
{ "_id" : ObjectId("5cbdf912ac184d684e3fa266"), "StudentName" : "Carol" }
{ "_id" : ObjectId("5cbdf916ac184d684e3fa267"), "StudentName" : "Sam" }
{ "_id" : ObjectId("5cbdf91bac184d684e3fa268"), "StudentName" : "Mike" }

Kiểm tra document có StudentName = "Carol":

> db.checkExistingDemo.findOne({StudentName: 'Carol'});

Kết quả:

{ "_id" : ObjectId("5cbdf912ac184d684e3fa266"), "StudentName" : "Carol" }