Mongo Shell By Example

Start the mongo shell

Start the mongo shell by running mongo

Note: this will connect using the default port 27017. Use -p for specifying a different port.

You should get an output similar to the following

MongoDB shell version v4.0.3
connecting to: mongodb://127.0.0.1:27017
Implicit session: session { "id" : UUID("2323-8as8-23aa-8fsa") }
MongoDB server version: 4.0.3
>

From this moment on, everything you’ll type will be executed in the mongo shell.

List databases

Your server may host several different databases you have access to. Run show dbsto list the databases

> show dbs
admin      0.000GB
config     0.000GB
fullstack  0.000GB
local      0.000GB
rhoci      0.000GB

There are two databases which I created: rhoci and fullstack. The rest is created by default and you should see them in your environment as well.

Switch database

By default, you’ll be using the ‘test’ database. You can verify it by using the db command. The reason it’s not listed in show dbs is that it’s an empty database. Meaning, there are no documents in it.

In order to switch to another database, run use <DB_name>

> use rhoci
switched to db rhoci

We switched from the data testto the database rhoci

List collections

To list all the collections in your database simply run show collectinos

> show collections
jobs

You can see we have one collection named ‘jobs’.

Query all documents

To query for all of our documents in the ‘jobs’ collection, we’ll use thefindcommand with a blank expression.

> db.jobs.find({})
{ "_id" : ObjectId("5c7e7de5a69b772f445113ff"), "name" : "job1", "created_date" : ISODate("2019-03-05T13:47:17.103Z") }
{ "_id" : ObjectId("5c7e7de5a69b772f44511400"), "name" : "job2", "created_date" : ISODate("2019-03-05T13:47:17.105Z") }
{ "_id" : ObjectId("5c7e7de5a69b772f44511401"), "name" : "job3", "created_date" : ISODate("2019-03-05T13:47:17.106Z") }

We have three 3 documents in ‘jobs’ collection. Each has an id, name, and created_date.

Query for a specific document

To query for one, specific document all you have to do is to specify equality conditions this way

> db.jobs.find({name: "job3"})
{ "_id" : ObjectId("5c7e7de5a69b772f44511401"), "name" : "job3", "created_date" : ISODate("2019-03-05T13:47:17.106Z") }

We queried for a job whose name is “job3” and we got exactly one result as we have one document with the name ‘job3’.

Query using a regular expression

Sometimes you will want to query for certain pattern rather than a specific document. Mongo supports regular expressions.

For example, the following command result will match only job1 and job2

> db.jobs.find({name: /job[1-2]/})
{ "_id" : ObjectId("5c7e7de5a69b772f445113ff"), "name" : "job1", "created_date" : ISODate("2019-03-05T13:47:17.103Z") }
{ "_id" : ObjectId("5c7e7de5a69b772f44511400"), "name" : "job2", "created_date" : ISODate("2019-03-05T13:47:17.105Z") }

Now let’s query for jobs whose name contains the digit 3

> db.jobs.find({name: /3/})
{ "_id" : ObjectId("5c7e7de5a69b772f44511401"), "name" : "job3", "created_date" : ISODate("2019-03-05T13:47:17.106Z") }

Insert a new document into a collection

To insert a single document into your collection, use db.<collection_name>.insertOne{...}

> db.jobs.insertOne({ name: 'job100'})
{
	"acknowledged" : true,
	"insertedId" : ObjectId("5c7fc155ef1b6e34f192")
}
> db.jobs.find({name: 'job100'})
{ "_id" : ObjectId("5c7fc155ef1b6e34f192"), "name" : "job100" }

Insert several documents at once

Similarly to what we did in the previous section, you can use db.<collection_name>.insertMany for inserting several documents

> db.jobs.insertMany([
... { name: 'job200' },
... { name: 'job300' },
... ])
{
	"acknowledged" : true,
	"insertedIds" : [
		ObjectId("5c7fc26aef531b6e34f193"),
		ObjectId("5c7fc26aef531b6e34f194")
	]}
> db.jobs.find({})
{ "_id" : ObjectId("5c7fc155ef531b6e34f192"), "name" : "job100" }
{ "_id" : ObjectId("5c7fc26aef531b6e34f193"), "name" : "job200" }
{ "_id" : ObjectId("5c7fc26aef531b6e34f194"), "name" : "job300" }

Delete all documents

The following will remove all documents from ‘jobs’ collection

> db.jobs.deleteMany({})
{ "acknowledged" : true, "deletedCount" : 3 }

You can see it removed a total of 3 documents.

Delete one specific document

The following will remove only ‘job100’ document

> db.jobs.deleteOne( { name: "job100" } )
{ "acknowledged" : true, "deletedCount" : 1 }

Try for yourself: what happens when you have two documents with job name ‘job100’ and you run the above command?

Delete documents using regex

Let’s remove all the documents of jobs whose name includes 2 and above

> db.jobs.deleteOne( { name: /[3-9]/ } )
{ "acknowledged" : true, "deletedCount" : 1 }

Delete collection

To remove a collection, use the db.<collection_name>.drop() syntax.

> db.jobs.drop()
true

If the collection was deleted successfully, you’ll get ‘true’. Otherwise you would get ‘false’ and that could mean a couple of things. The most common one is probably a simple typo in collection name.

That’s it. If you enjoyed reading this post or have any additional questions, feel free to leave a comment below.