MongoDB doesn’t have a CREATE DATABASE statement like SQL does.

In MongoDB, you create a database simply by switching to a non-existent database, then inserting data.

Example

Here’s an example of creating a new database:

use PetHotel

Result:

switched to db PetHotel 

That creates a new database called PetHotel and makes it the current database.

However, the database is only partially created. It isn’t fully created until you insert data.

If we run the show dbs command to see what databases we have, it won’t be shown.

show dbs

Result:

 admin   0.000GB
 config  0.000GB
 local   0.000GB 

This is the default set of databases that were installed with MongoDB. If you have other databases, you’ll see them here too.

But the point is, our newly created PetHotel database is nowhere to be seen!

Insert Data

To fully create the database, we need to insert some data. Even just a small amount is enough.

Example:

db.pets.insert({ name: "Fetch" })

Result:

 WriteResult({ "nInserted" : 1 }) 

This message tells us that one document was inserted.

Now when we run show dbs again, we can see our newly created database.

show dbs

Result:

 PetHotel  0.000GB
 admin     0.000GB
 config    0.000GB
 local     0.000GB 

Collections

A database contains collections. In our case, we’ve already created a collection called pets.

When you insert data, you use the syntax like this:

db.<collection>.insert()

Where <collection> is the name of the collection to insert data into. If the collection doesn’t exist, it will be created.

In our case, we used the following command:

db.pets.insert({ name: "Fetch" })

Which created a collection called pets (because it didn’t already exist).

Check the Data

You can use the find() collection method to check the data in the collection.

Example:

db.pets.find()

Result:

 { "_id" : ObjectId("5fe02d3937b49e0faf1af20b"), "name" : "Fetch" } 

As expected, our document is returned.

You’ll notice that it also has an extra field. It has an _id field, which we didn’t specify when we added the document.

The _id field is a special field. It’s used as an identifier for the document. If the document does not specify an _id field, then MongoDB will add the _id field and assign a unique ObjectId for the document before inserting.

Alternatively, you can provide your own _id field and assign it your own value. However, note that the _id value must be unique within the collection to avoid duplicate key error.