This post will explain how to do UPSERT statements in MongoDB. Before we start let's first describe what an UPSERT statement is. An UPSERT statement will insert a row if it doesn't exist already, if the row does exist then it will update the row. In SQL Server or Oracle you would use the MERGE statement. In MongDB, you can supply the upsert option in the argument. We will take a look at how that all works later in this post.

Open up a new command prompt or shell, connect to MongoDB and either use an existing database or create a new one

If you need some help with setting up MongoDB on Windows 7 or Windows 8, take a look at Creating MongoDB as a service on Windows 8

Let's do a simple insert, run the following

db.things.insert( { name : "Denis1"} )

Now let's bring back what we just inserted

db.things.find({name : "Denis1"})

Here is the result
{ "_id" : ObjectId("50f1778ea5ec290b7773303b"), "name" : "Denis1" }

Just a warning, the ObjectId which is 50f1778ea5ec290b7773303b here will be different on your system.

If we want to update that from Denis1 to Denis2, we can use the following

db.things.update({name: "Denis1"}, {name: "Denis2"})

Now if you run this again, you won't get anything back

db.things.find({name : "Denis1"})

If instead you use Denis2, you will get the row back

db.things.find({name : "Denis2"})

{ "_id" : ObjectId("50f1778ea5ec290b7773303b"), "name" : "Denis2" }

Just to make sure that you have only one thing in the collection run the following

db.things.find()

You should back one thing only
{ "_id" : ObjectId("50f1778ea5ec290b7773303b"), "name" : "Denis2" }

Time to look at the upsert command
When you run the following, Denis6 will be inserted, Denis5 does not exist, there is nothing to update so Denis6 gets inserted

db.things.update({name : "Denis5"}, {name: "Denis6"}, true);

If you do a search for Denis6, you will get it back from the collection

db.things.find({name : "Denis6"})

{ "_id" : ObjectId("50f1793d41c33bd2459aafeb"), "name" : "Denis6" }

Instead of just specifying true in the options you can also name it to make it more clear, it will look like this { upsert: true }

Run this command, it will update Denis6 to Denis7

db.things.update({name : "Denis6"}, {name: "Denis7"}, { upsert: true });

db.things.find({name : "Denis7"})

{ "_id" : ObjectId("50f1793d41c33bd2459aafeb"), "name" : "Denis7" }

Upsert example with an incremented counter

in this part we will use the $inc operator. The $inc operator increments a value by a specified amount if field is present in the document. If the field does not exist, $inc sets field to the number value.

Let's get started, let's say we want to track how many hits a certain page gets, let's say this page is named How To Do Upserts, everytime someone hits that page we will increment the hits counter. Here is what we will execute

db.things.update({BlogPost: "How To Do Upserts"}, {$inc: {Hits: 1}}, { upsert: true });

Now if we look in the collection

db.things.find({BlogPost : "How To Do Upserts"})

Here is what is returned, as you can see hits is 1
{ "_id" : ObjectId("50f17b4541c33bd2459aafed"), "BlogPost" : "How To Do Upserts", "Hits" : 1 }
Let's run that same update statement two more times

db.things.update({BlogPost: "How To Do Upserts"}, {$inc: {Hits: 1}}, { upsert: true });
db.things.update({BlogPost: "How To Do Upserts"}, {$inc: {Hits: 1}}, { upsert: true });

Now if we look in the collection again

db.things.find({BlogPost : "How To Do Upserts"})

{ "_id" : ObjectId("50f17b4541c33bd2459aafed"), "BlogPost" : "How To Do Upserts", "Hits" : 3 }

As you can see the hits counter has now increased to 3.

Here is also the whole command window output in case you find it easier to follow along like that

That is all for this post, in the next post we will look at some more interesting stuff