mongodb/tutorial.md

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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
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of the Haskell mongoDB drivers. It is modeled after the
[pymongo tutorial](http://api.mongodb.org/python/1.4%2B/tutorial.html).
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You will need the mongoDB bindings installed as well as mongo itself installed.
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$ = command line prompt
> = ghci repl prompt
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Installing Haskell Bindings
---------------------------
From Source:
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$ git clone git://github.com/srp/mongoDB.git
$ cd mongoDB
$ runhaskell Setup.hs configure
$ runhaskell Setup.hs build
$ runhaskell Setup.hs install
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From Hackage using cabal:
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$ cabal install mongoDB
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Getting Ready
-------------
Start a MongoDB instance for us to play with:
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$ mongod
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Start up a haskell repl:
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$ ghci
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Now We'll need to bring in the MongoDB/BSON bindings:
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> import Database.MongoDB
> import Database.MongoDB.BSON
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Making A Connection
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-------------------
Open up a connection to your DB instance, using the standard port:
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> con <- connect "127.0.0.1" []
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or for a non-standard port
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> 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:
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> con <- connect "127.0.0.1" [SlaveOK]
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Databases, Collections and FullCollections
------------------------------------------
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As many database servers, MongoDB has databases--separate namespaces
under which collections reside. Most of the APIs for this driver
request the *FullCollection* which is simply the *Database* and the
*Collection* concatenated with a period.
For instance 'myweb_prod.users' is the the *FullCollection* name for
the *Collection 'users' in the database 'myweb_prod'.
Databases and collections do not need to be created, just start using
them and MongoDB will automatically create them for you.
In the below examples we'll be using the following *FullCollection*:
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> import Data.ByteString.Lazy.UTF8
> let testcol = (fromString "test.haskell")
You can obtain a list of databases available on a connection:
> dbs <- databaseNames con
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You can obtain a list of collections available on a database:
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> collections <- collectionNames con (fromString "test")
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Documents
---------
Data in MongoDB is represented (and stored) using JSON-style
documents. In mongoDB we use the *BsonDoc* type to represent these
documents. At the moment a *BsonDoc* is simply a tuple list of the
type '[(ByteString, BsonValue)]'. Here's a BsonDoc which could represent
a blog post:
> import Data.Time.Clock.POSIX
> now <- getPOSIXTime
> :{
let post = [(fromString "author", BsonString $ fromString "Mike"),
(fromString "text",
BsonString $ fromString "My first blog post!"),
(fromString "tags",
BsonArray [BsonString $ fromString "mongodb",
BsonString $ fromString "python",
BsonString $ fromString "pymongo"]),
(fromString "date", BsonDate now)]
:}
With all the type wrappers and string conversion, it's hard to see
what's actually going on. Fortunately the BSON library provides
conversion functions *toBson* and *fromBson* for converting native
between the wrapped BSON types and many native Haskell types. The
functions *toBsonDoc* and *fromBsonDoc* help convert from tuple lists
with plain *String* keys, or *Data.Map*.
Here's the same BSON data structure using these conversion functions:
> :{
let post = toBsonDoc [("author", toBson "Mike"),
("text", toBson "My first blog post!"),
("tags", toBson ["mongoDB", "Haskell"]),
("date", BsonDate now)]
:}
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Inserting a Document
-------------------
> insert con testcol post
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Getting a single document with findOne
-------------------------------------
> findOne con testcol (toBsonDoc [("author", toBson "Mike")])
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Querying for More Than One Document
------------------------------------
> cursor <- find con testcol (toBsonDoc [("author", toBson "Mike")])
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> allDocs cursor
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You can combine these into one line:
> docs <- allDocs =<< find con testcol (toBsonDoc [("author", toBson "Mike")])
See nextDoc to modify cursor incrementally one at a time.
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* Note: allDocs automatically closes the cursor when done, through nextDoc.
Counting
--------
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We can count how many documents are in an entire collection:
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> num <- count con testcol
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Or we can query for how many documents match a query:
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> num <- countMatching con testcol (toBsonDoc [("author", toBson "Mike")])
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Range Queries
-------------
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No non native sorting yet.
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Indexing
--------
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WIP - coming soon.
Something like...
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> index <- createIndex con testcol [("author", Ascending)] True