mongodb/tutorial.md

MongoDB Haskell Mini Tutorial

Author: Brian Gianforcaro (b.gianfo@gmail.com)

Updated: 2/28/2010

This is a mini tutorial to get you up and going with the basics of the Haskell mongoDB drivers. It is modeled after the python tutorial pymongo available here: http://api.mongodb.org/python/1.4%2B/tutorial.html

You will need the mongoDB bindings installed as well as mongo itself installed.

$ = command line prompt = ghci repl prompt

Installing Haskell Bindings

From Source:

$ git clone git://github.com/srp/mongoDB.git

$ cd mongoDB

$ runhaskell Setup.hs configure

$ runhaskell Setup.hs build

$ runhaskell Setup.hs install

From Hackage using cabal:

$ cabal install mongoDB

Getting Ready

Start a MongoDB instance for us to play with:

$ mongod

Start up a haskell repl:

$ ghci

Now We'll need to bring in the MongoDB/BSON bindings:

import Database.MongoDB

import Database.MongoDB.BSON

Making A Connection

Open up a connection to your DB instance, using the standard port:

con <- connect "127.0.0.1" []

or for a non-standard port

import Network con <- connectOnPort "127.0.0.1" (Network.PortNumber 666) []

By default mongoDB will try to find the master and connect to it and will throw an exception if a master can not be found to connect to. You can force mongoDB to connect to the slave by adding SlaveOK as a connection option, eg:

con <- connect "127.0.0.1" [SlaveOK]

Getting the Databases

dbs <- databaseNames con let testdb = head dbs

Getting the Collections

collections <- collectionNames con testdb let testcol = head collections

Documents

BSON representation in Haskell

Inserting a Document

insert con testcol (toBsonDoc [("author", toBson "Mike"), ("text", toBson "My first Blog post!"), ("tags", toBson ["mongodb", "python","pymongo"])])

Getting a single document with findOne

findOne con curcol (toBsonDoc [("author", toBson "Mike")])

Querying for More Than One Document

cursor <- find con curcol (toBsonDoc [("author", toBson "Mike")])

allDocs cursor

You can combine these into one line:

docs <- allDocs =<< find con curcol (toBsonDoc [("author", toBson "Mike")])

See nextDoc to modify cursor incrementally one at a time.

• Note: allDocs automatically closes the cursor when done, through nextDoc.

Counting

We can count how many documents are in an entire collection:

num <- count con testcol

Or we can query for how many documents match a query:

num <- countMatching con testcol (toBsonDoc [("author", toBson "Mike")])

Range Queries

No non native sorting yet.

Indexing

WIP - coming soon.

Something like...

index <- createIndex con testcol [("author", Ascending)] True