mongodb.md

MongoDB

Some minimal notes on installing and using MongoDB.

Installation and startup

This is for simplistic local single server use, just including the databse and the shell.

The community edition is at https://www.mongodb.com/try/download/community (version 8.0.4 as of February 2025) and the MongoDB Shell is at https://www.mongodb.com/try/download/shell (version 2.3.9). The README file of the community edition has some basic information that may work in some cases, but on my Mac I needed a bit more which I found at https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-os-x-tarball/. This was partially to avoid using my screwed up brew environment.

Installation is a matter of unpacking the archive, creating directories for the database and the log files, and starting the server. For that do the following (assuming you are in the unpacked MongoDB archive):

$ sudo mkdir -p data/db
$ sudo mkdir data/log
$ bin/mongod --dbpath data/db --logpath data/log/mongo.log --fork

about to fork child process, waiting until server is ready for connections.
forked process: 59917
child process started successfully, parent exiting

You can put the data and logs elsewhere if you like.

Now you need to run a mongo database shell named mongosh (https://www.mongodb.com/docs/mongodb-shell/). Install and start by unpacking the archive and running mongosh (from the unpacked archive):

$ bin/mongosh

If MongoDB had been installed as a service or via Brew, then you would something like service mongodb stop, but since this is a simplistic basic install you either use kill -9 PROCESS_ID or you stop it from the shell:

test> db.adminCommand({ "shutdown" : 1 })

Use ctrl-d to exit the shell.

Example Usage

All examples are from the shell. The manual is at https://docs.mongodb.com/manual/.

In the shell you can use a database (which will be created if it does not exist yet):

test> use movies
switched to db movies
movies> 

From here on, I will usually leave out the movies prompt.

A database consists of collections and you can add a new document to a collection in the database:

db.movies.insertOne(
  {
    title: "The Favourite",
    genres: [ "Drama", "History" ],
    runtime: 121,
    rated: "R",
    year: 2018,
    directors: [ "Yorgos Lanthimos" ],
    cast: [ "Olivia Colman", "Emma Stone", "Rachel Weisz" ],
    type: "movie"
  }
)

{
  acknowledged: true,
  insertedId: ObjectId('67aff4f9c5c750f260fe4240')
}

As with databases, a collection will be created if it did not exist yet. This example is somewhat confusing because the database and the collection in it have the same name:

movies> show dbs
admin   40.00 KiB
config  72.00 KiB
local   72.00 KiB
movies  80.00 KiB
movies> show collections
movies

There four databases in the MongoDB server: the one we just created and three system databases (admin, config and local). The one we created has one collection (which is the equivalent of an SQL table and an Elasticsearch index).

Inserting multiple documents:

db.movies.insertMany([
   {
      title: "Jurassic World: Fallen Kingdom",
      genres: [ "Action", "Sci-Fi" ],
      runtime: 130,
      rated: "PG-13",
      year: 2018,
      directors: [ "J. A. Bayona" ],
      cast: [ "Chris Pratt", "Bryce Dallas Howard", "Rafe Spall" ],
      type: "movie"
    },
    {
      title: "Tag",
      genres: [ "Comedy", "Action" ],
      runtime: 105,
      rated: "R",
      year: 2018,
      directors: [ "Jeff Tomsic" ],
      cast: [ "Annabelle Wallis", "Jeremy Renner", "Jon Hamm" ],
      type: "movie"
    }
])

{
  acknowledged: true,
  insertedIds: {
    '0': ObjectId('67aff4a8c5c750f260fe423e'),
    '1': ObjectId('67aff1c3c5c750f260fe4239')
  }
}

You query with the find function which runs on a collection:

db.movies.find( {genres:"Comedy"} )

[
  {
    _id: ObjectId('67aff1c3c5c750f260fe4239'),
    title: 'Tag',
    genres: [ 'Comedy', 'Action' ],
    runtime: 105,
    rated: 'R',
    year: 2018,
    directors: [ 'Jeff Tomsic' ],
    cast: [ 'Annabelle Wallis', 'Jeremy Renner', 'Jon Hamm' ],
    type: 'movie'
  }
]

To get all documents do db.movies.find({}).

Let's now try:

db.movies.insertOne( { x: 1 } );

{
  acknowledged: true,
  insertedId: ObjectId('67aff3bbc5c750f260fe423b')
}

db.movies.insertOne( { x: {y: 1, z: 2 } } );

{
  acknowledged: true,
  insertedId: ObjectId('67aff3dac5c750f260fe423c')
}

This inserts totally different kinds of documents, but MongoDB allows that.

You can search for a path:

db.movies.find({"x.y":1});

[ { _id: ObjectId('67aff3dac5c750f260fe423c'), x: { y: 1, z: 2 } } ]

To empty a collection:

db.movies.deleteMany({})

Updating:

db.movies.updateOne( 
  { title: "Tag" }, 
  { $set: { plot: "One month every year, five highly competitive friends hit the ground running for a no-holds-barred game of tag" },
    $currentDate: { lastUpdated: true } }
)

{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}

db.movies.find( {genres:"Comedy"} )

[
  {
    _id: ObjectId('67aff4a8c5c750f260fe423f'),
    title: 'Tag',
    genres: [ 'Comedy', 'Action' ],
    runtime: 105,
    rated: 'R',
    year: 2018,
    directors: [ 'Jeff Tomsic' ],
    cast: [ 'Annabelle Wallis', 'Jeremy Renner', 'Jon Hamm' ],
    type: 'movie',
    lastUpdated: ISODate('2025-02-15T02:05:01.086Z'),
    plot: 'One month every year, five highly competitive friends hit the ground running for a no-holds-barred game of tag'
  }
]