Transaction lock in MongoDB?

Transaction support isn’t available in MongoDB 4.0. To get similar results, use findOneAndUpdate().

Let us create a collection with documents −

> db.demo404.insertOne({"FirstName":"John"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e6f8c38fac4d418a0178592")
}
> db.demo404.insertOne({"FirstName":"Robert"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e6f8c3cfac4d418a0178593")
}
> db.demo404.insertOne({"FirstName":"Mike"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e6f8c40fac4d418a0178594")
}

Display all documents from a collection with the help of find() method −

> db.demo404.find();

This will produce the following output −

{ "_id" : ObjectId("5e6f8c38fac4d418a0178592"), "FirstName" : "John" }
{ "_id" : ObjectId("5e6f8c3cfac4d418a0178593"), "FirstName" : "Robert" }
{ "_id" : ObjectId("5e6f8c40fac4d418a0178594"), "FirstName" : "Mike" }

Following is the query to use findOneAndUpdate and set lock in MongoDB −

> result=db.demo404.findOneAndUpdate({"in_transaction": {"$exists": false}}, {"$set": {"in_transaction": true}});

This will produce the following output −

{ "_id" : ObjectId("5e6f8c38fac4d418a0178592"), "FirstName" : "John" }