Using MongoDB

Connect to / Import into a Database

First, let’s connect to our server through the mongo shell program:

mongo

MongoDB shell version: 3.2.3
connecting to: test

A MongoDB instance can host multiple databases, which are created dynamically. In the shell, you can type show dbs to see what exists already. In general, you can type help to see a list of available commands.

Let’s tell mongo we want to use swc, i.e. use a database with the name swc. Mongo will create the database for us if it doesn’t exist.

// Refer to the Software Carpentry ("swc") database
use swc

switched to db swc

The mongo shell, in addition to responding to its special command language, is also a JavaScript interpreter. Comment lines in Javascript are preceded with //, so the line before use swc above is a comment.

A MongoDB database is organized as a set of collections, each of which contains a set of documents. Just as with databases themselves, database collections are created dynamically in MongoDB. Let’s ask for a count of the number of documents in the materials collection of our database:

db.materials.count()

0

This is to be expected – we have no documents in the (hypothetical) swc database’s (hypothetical) materials collection. Let’s make things more real by importing some data. exit out of the mongo shell and let’s use mongoimport to load some documents into swc.materials:

exit

bye

mongoimport mongo-novice-materials.json --db swc --collection materials --jsonArray

connected to: localhost
imported 66140 documents

JSON, which stands for “Javascript Object Notation”, is a way to express simple data structures that is widely used in many applications, particularly in web-based applications. We’ll go over the format in the next topic when we construct a document to insert into our collection, but for now let’s focus on importing data that we’re given.

Now, let’s re-enter the shell and get a count of our collection:

mongo
use swc
db.materials.count()

66140

mongoimport is a flexible way to import data into a database collection. If you exit the shell, you can enter mongoimport --help to get a sense of the options available. In particular, importing of data stored in tab-separated-values (TSV) or comma-separated-values (CSV) formats are supported.

mongorestore is a command to restore an entire database (i.e., multiple collections) from a backup. mongodump is a command to “dump” a database for backup.

db.publications.count()