The mongo shell is equivalent to the administration console used by relational databases. Connecting to the mongo shell is as easy as typing the following code:

$ mongo

Type this on the command line for standalone servers or replica sets. Inside the shell, you can view available databases simply by typing the following code:

$ db

Then, you can connect to a database by typing the following code:

> use <database_name>

The mongo shell can be used to query and update data into our databases. Inserting this document in the books collection can be done as follows:

> db.books.insert({title: 'mastering mongoDB', isbn: '101'})
WriteResult({ "nInserted" : 1 })

We can then find documents from a collection named books by typing the following:

> db.books.find()
{ "_id" : ObjectId("592033f6141daf984112d07c"), "title" : "mastering mongoDB", "isbn" : "101" }

The result we get back from MongoDB informs us that the write succeeded and inserted one new document in the database.

Deleting this document has a similar syntax and results in the following code:

> db.books.remove({isbn: '101'})
WriteResult({ "nRemoved" : 1 })

You can try to update this same document as shown in the following code block:

> db.books.update({isbn:'101'}, {price: 30})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.books.find()
{ "_id" : ObjectId("592034c7141daf984112d07d"), "price" : 30 }

Here, we notice a couple of things:

• The JSON-like formatted field in the update command is our query for searching for documents to update
• The WriteResult object notifies us that the query matched one document and modified one document
• Most importantly, the contents of this document were entirely replaced by the contents of the second JSON-like formatted field but we have lost information on title and isbn

By default, the update command in MongoDB will replace the contents of our document with the document we specify in the second argument. If we want to update the document and add new fields to it, we need to use the $set operator, as follows:

> db.books.update({isbn:'101'}, {$set: {price: 30}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Now, our document matches what we would expect:

> db.books.find()
{ "_id" : ObjectId("592035f6141daf984112d07f"), "title" : "mastering mongoDB", "isbn" : "101", "price" : 30 }

However, deleting a document can be done in several ways, the most simple way is through its unique ObjectId:

> db.books.remove("592035f6141daf984112d07f")
WriteResult({ "nRemoved" : 1 })
> db.books.find()
>

You can see here that when there are no results, the mongo shell will not return anything other than the shell prompt itself: >.