Learn how to perform CRUD operations on a MongoDB database, using the mongo shell
While it is likely that you will want to leverage MongoDB for your Node.js application, the mongo shell is an incredibly useful administrative tool that should not be overlooked. The definition provided by mongodb.org is: “The mongo shell is an interactive JavaScript shell for MongoDB, and is part of all MongoDB distributions.” It really is that straightforward: you can interact with your MongoDB database using JavaScript, in a command shell. Brilliant.
In this article I will demonstrate how to create a MongoDB database, add documents to the database, update a document, delete a document, and then delete your database. All of this will be done using a command prompt and JavaScript.
NOTE: I assume that you already have MongoDB installed globally. If you do not have MongoDB installed and need assistance with that, please see the “Installation Links” section at the end of this article.
Starting the Mongo shell
Before you can interact with a MongoDB database using the mongo shell, you’ll need to have the MongoDB database server running. In order to start the MongoDB server, execute: “mongod” in your terminal window. The output you see should be similar to this:
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mongod --help for help and startup options 2015-03-22T13:09:24.130-0400 [initandlisten] MongoDB starting : pid=1562 port=27017 dbpath=/data/db 64-bit host=YOUR_MACHINE_NAME.local 2015-03-22T13:09:24.130-0400 [initandlisten] db version v2.6.5 |
Starting the Mongo shell couldn’t be easier. Open a second terminal window, and then execute the command: “mongo”. You should see the following output in your terminal window:
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MongoDB shell version: 2.6.5 connecting to: test |
You may be surprised to see that you are connected to “test”, but that is the default database. In order to see a list of existing databases, execute the following command:
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show dbs |
You should see the following output in your terminal window:
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admin (empty) |
Creating a MongoDB Database
In order to create a new database, use the “use” command. Execute the following command:
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use madMen |
You should see the following output in your terminal window:
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switched to db madMen |
Now take a look at the existing databases again by executing the command: “show dbs”. You may be wondering why the new database “madMen” does not show up in the list of existing databases. This is because it has no data. Let’s add some data to that database.
Adding Documents to a Collection
With MongoDB, we can create collections on the fly when we add data. For example, the new database “madMen” is empty. We can add a “names” collection and insert a document into that collection all in one command.
Execute this command:
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db.names.insert({'name' : 'Don Draper'}); |
You should see the following output in your terminal:
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WriteResult({ "nInserted" : 1 }) |
Now, let’s take another look at the list of databases. Execute the command: “show dbs”.
You should see the following output in your terminal:
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admin (empty) madMen 0.078GB |
The reason you now see the madMen database in the list is because it contains some data. Let’s add three more documents to the “names” collection. Execute the following commands:
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db.names.insert({'name' : 'Pete Campbell'}); db.names.insert({'name' : 'Betty Draper'}); db.names.insert({'name' : 'Joan Harris'}); |
If you executed the previous JavaScript, the “names” collection should now have four documents. Let’s talk about how you can view all the documents in a collection.
Iterating Over the Documents in a Collection
If you want to view all of the documents in a collection, using the mongo shell, it is at minimum, a two-step process. First, obtain a reference to the collection, and then iterate over the collection using the next() method. In the following example, we’ll create a while loop. The hasNext() method will be used as the condition of the loop, and then inside of the loop, we’ll use the next() method to get the “next” document in the collection. The return value of that method will be passed to the printJson function, which is specific to mongo.
Execute this code:
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var allRecords = db.names.find(); while ( allRecords.hasNext() ) { printjson(allRecords.next()); } |
In the previous example, we set the variable “allRecords” equal to the result of “db.names.find()”. The “allRecords” variable then has a reference to all of the documents in the “names” collection. We then use a while loop to iterate over the collection. On each iteration, the next method of the allRecords variable is passed to the printjson function. The output in your terminal should be similar to this:
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{ "_id" : ObjectId("550ef996bca11fc0a6df88d0"), "name" : "Don Draper" } { "_id" : ObjectId("550efb31ec7714832416d885"), "name" : "Pete Campbell" } { "_id" : ObjectId("550efb31ec7714832416d886"), "name" : "Betty Draper" } { "_id" : ObjectId("550efb32ec7714832416d887"), "name" : "Joan Harris" } |
The values of each document’s “_id” property will differ in your terminal because these are unique IDs, generated by the instance of MongoDB. The rest of the data should be the same.
Updating a Document
Now that we have four documents in the “names” collection, let’s update one of those documents. We do this by using the “save” method of the collection object. We’ll need to pass the “_id” of the document that we want to update, as well as the new data. Let’s change “Don Draper” to “Dick Whitman”.
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db.names.save({_id:ObjectId('550ef996bca11fc0a6df88d0'),"name" : "Dick Whitman" }); |
You should see the following output in your terminal:
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WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 }); |
Now, let’s use the while loop we created earlier to inspect all records of the “names” collection:
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var allRecords = db.names.find(); while ( allRecords.hasNext() ) { printjson(allRecords.next()); } |
You should see the following output in your terminal:
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{ "_id" : ObjectId("550ef996bca11fc0a6df88d0"), "name" : "Dick Whitman" } { "_id" : ObjectId("550efb31ec7714832416d885"), "name" : "Pete Campbell" } { "_id" : ObjectId("550efb31ec7714832416d886"), "name" : "Betty Draper" } { "_id" : ObjectId("550efb32ec7714832416d887"), "name" : "Joan Harris" } |
As you can see, the document that contained “Don Draper” has now been changed to “Dick Whitman”.
Deleting a Document
Let’s delete the same document that we just updated. In order to do that, we’ll use the “remove” method of the collection object, passing it the “_id” of the exact document that we want to delete:
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db.names.remove({_id:ObjectId('550ef996bca11fc0a6df88d0')}); |
You should see the following output in your terminal:
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WriteResult({ "nRemoved" : 1 }) |
Now let’s take a look at all the documents in the database again:
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var allRecords = db.names.find(); while ( allRecords.hasNext() ) { printjson(allRecords.next()); } |
As you can see, the document that we deleted no longer exists.
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{ "_id" : ObjectId("550efb31ec7714832416d885"), "name" : "Pete Campbell" } { "_id" : ObjectId("550efb31ec7714832416d886"), "name" : "Betty Draper" } { "_id" : ObjectId("550efb32ec7714832416d887"), "name" : "Joan Harris" } |
Deleting a Database
While not something you are likely to do too often, deleting a database is a perfectly valid MongoDB operation. The syntax could not be more simple; use the “dropDatabase” method of the db object.
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db.dropDatabase(); |
You should see the following output in your terminal:
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{ "dropped" : "madMen", "ok" : 1 } |
Now, execute the command: “show dbs”. You should see the following output in your terminal:
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admin (empty) |
Summary
In this article, we learned about basic CRUD operations in Mongo Shell. We learned how to start the database server, start the shell and view a list of all databases. We also covered steps needed to create a database, add documents to that database, update a document, delete a document and delete a database. There is a mountain of topics when it comes to the Mongo Shell. I hope this article helped you in getting started.
Helpful Links for the mongo shell
General Links
http://docs.mongodb.org/manual/crud/
http://docs.mongodb.org/v2.2/mongo/
http://www.tutorialspoint.com/mongodb/
Installation Links
Install MongoDB on OS X — MongoDB Manual 3.0.1
http://docs.mongodb.org/manual/tutorial/install-mongodb-on-os-x/
Install MongoDB on Windows — MongoDB Manual 3.0.1
http://docs.mongodb.org/manual/tutorial/install-mongodb-on-windows/
Install on Linux — MongoDB Manual 3.0.1
http://docs.mongodb.org/manual/administration/install-on-linux/
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