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Rename Connection to ConnPool. Edit tutorial and some comments

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This commit is contained in:
Tony Hannan 2010-10-31 20:38:38 -04:00
parent ad13914862
commit 36cc86fd70
9 changed files with 118 additions and 124 deletions
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3
Control/Monad/Util.hs
View file

@ -20,9 +20,6 @@ instance (Monad m, Error e) => Applicative (ErrorT e m) where
class (MonadIO m, Applicative m, Functor m) => MonadIO' m
instance (MonadIO m, Applicative m, Functor m) => MonadIO' m
ignore :: (Monad m) => a -> m ()
ignore _ = return ()
loop :: (Functor m, Monad m) => m (Maybe a) -> m [a]
-- ^ Repeatedy execute action, collecting results, until it returns Nothing
loop act = act >>= maybe (return []) (\a -> (a :) <$> loop act)

4
Database/MongoDB.hs
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@ -10,8 +10,8 @@ Simple example below. Use with language extension /OvererloadedStrings/.
> import Control.Monad.Trans (liftIO)
>
> main = do
> conn <- connect 1 (host "127.0.0.1")
> e <- access safe Master conn run
> pool <- newConnPool 1 (host "127.0.0.1")
> e <- access safe Master pool run
> print e
>
> run = use (Database "baseball") $ do

87
Database/MongoDB/Connection.hs
View file

@ -1,16 +1,16 @@
{- | A Mongo connection is a pool of TCP connections to a single server or a replica set of servers. -}
{- | A pool of TCP connections to a single server or a replica set of servers. -}
{-# LANGUAGE OverloadedStrings, ScopedTypeVariables, RecordWildCards, MultiParamTypeClasses, FlexibleContexts, TypeFamilies, DoRec, RankNTypes #-}
{-# LANGUAGE OverloadedStrings, ScopedTypeVariables, RecordWildCards, NamedFieldPuns, MultiParamTypeClasses, FlexibleContexts, TypeFamilies, DoRec, RankNTypes, FlexibleInstances #-}
module Database.MongoDB.Connection (
-- * Host
Host(..), PortID(..), host, showHostPort, readHostPort, readHostPortM,
-- * ReplicaSet
ReplicaSet(..),
ReplicaSet(..), Name,
-- * MasterOrSlaveOk
MasterOrSlaveOk(..),
-- * Connection
Server(..), replicaSet
-- * Connection Pool
Server(..), connHost, replicaSet
) where
import Database.MongoDB.Internal.Protocol
@ -30,6 +30,7 @@ import Database.MongoDB.Internal.Util () -- PortID instances
import Var.Pool
import System.Random (newStdGen, randomRs)
import Data.List (delete, find, nub)
import System.IO.Unsafe (unsafePerformIO)
type Name = UString
@ -103,7 +104,7 @@ getReplicaInfo pipe = do
return info
type ReplicaInfo = Document
-- ^ Configuration info of a host in a replica set. Contains all the hosts in the replica set plus its role in that set (master, slave, or arbiter)
-- ^ Configuration info of a host in a replica set (result of /ismaster/ command). Contains all the hosts in the replica set plus its role in that set (master, slave, or arbiter)
{- isPrimary :: ReplicaInfo -> Bool
-- ^ Is the replica described by this info a master/primary (not slave or arbiter)?
@ -139,42 +140,45 @@ data MasterOrSlaveOk =
isMS Master i = isPrimary i
isMS SlaveOk i = isSecondary i || isPrimary i -}
-- * Connection
-- * Connection Pool
type Pool' = Pool IOError
-- | A Server is a single server ('Host') or a replica set of servers ('ReplicaSet')
class Server t where
data Connection t
-- ^ A Mongo connection is a pool of TCP connections to a host or a replica set of hosts
connect :: (MonadIO' m) => Int -> t -> m (Connection t)
-- ^ Create a Mongo Connection to a host or a replica set of hosts. Actual TCP connection is not attempted until 'getPipe' request, so no IOError can be raised here. Up to N TCP connections will be established to each host.
getPipe :: MasterOrSlaveOk -> Connection t -> ErrorT IOError IO Pipe
data ConnPool t
-- ^ A pool of TCP connections ('Pipe's) to a host or a replica set of hosts
newConnPool :: (MonadIO' m) => Int -> t -> m (ConnPool t)
-- ^ Create a ConnectionPool to a host or a replica set of hosts. Actual TCP connection is not attempted until 'getPipe' request, so no IOError can be raised here. Up to N TCP connections will be established to each host.
getPipe :: MasterOrSlaveOk -> ConnPool t -> ErrorT IOError IO Pipe
-- ^ Return a TCP connection (Pipe) to the master or a slave in the server. Master must connect to the master, SlaveOk may connect to a slave or master. To spread the load, SlaveOk requests are distributed amongst all hosts in the server. Throw IOError if failed to connect to right type of host (Master/SlaveOk).
killPipes :: Connection t -> IO ()
-- ^ Kill all open pipes (TCP Connections). Will cause any users of them to fail. Alternatively you can let them die on their own when this Connection is garbage collected.
killPipes :: ConnPool t -> IO ()
-- ^ Kill all open pipes (TCP Connections). Will cause any users of them to fail. Alternatively you can let them die on their own when they are garbage collected.
-- ** Connection Host
-- ** ConnectionPool Host
instance Server Host where
data Connection Host = HostConnection {connHost :: Host, connPool :: Pool' Pipe}
data ConnPool Host = HostConnPool {connHost :: Host, connPool :: Pool' Pipe}
-- ^ A pool of TCP connections ('Pipe's) to a server, handed out in round-robin style.
connect poolSize' host' = liftIO (connectHost poolSize' host')
-- ^ Create a Connection (pool of TCP connections) to server (host or replica set)
newConnPool poolSize' host' = liftIO (newHostConnPool poolSize' host')
-- ^ Create a connection pool to server (host or replica set)
getPipe _ = getHostPipe
-- ^ Return a TCP connection (Pipe). If SlaveOk, connect to a slave if available. Round-robin if multiple slaves are available. Throw IOError if failed to connect.
killPipes (HostConnection _ pool) = killAll pool
killPipes (HostConnPool _ pool) = killAll pool
connectHost :: Int -> Host -> IO (Connection Host)
instance Show (ConnPool Host) where
show HostConnPool{connHost} = "ConnPool " ++ show connHost
newHostConnPool :: Int -> Host -> IO (ConnPool Host)
-- ^ Create a pool of N 'Pipe's (TCP connections) to server. 'getHostPipe' will return one of those pipes, round-robin style.
connectHost poolSize' host' = HostConnection host' <$> newPool Factory{..} poolSize' where
newHostConnPool poolSize' host' = HostConnPool host' <$> newPool Factory{..} poolSize' where
newResource = tcpConnect host'
killResource = close
isExpired = isClosed
getHostPipe :: Connection Host -> ErrorT IOError IO Pipe
getHostPipe :: ConnPool Host -> ErrorT IOError IO Pipe
-- ^ Return next pipe (TCP connection) in connection pool, round-robin style. Throw IOError if can't connect to host.
getHostPipe (HostConnection _ pool) = aResource pool
getHostPipe (HostConnPool _ pool) = aResource pool
tcpConnect :: Host -> ErrorT IOError IO Pipe
-- ^ Create a TCP connection (Pipe) to the given host. Throw IOError if can't connect.
@ -183,39 +187,42 @@ tcpConnect (Host hostname port) = ErrorT . E.try $ mkPipe =<< connectTo hostname
-- ** Connection ReplicaSet
instance Server ReplicaSet where
data Connection ReplicaSet = ReplicaSetConnection {
data ConnPool ReplicaSet = ReplicaSetConnPool {
repsetName :: Name,
currentMembers :: MVar [Connection Host] } -- master at head after a refresh
connect poolSize' repset = liftIO (connectSet poolSize' repset)
currentMembers :: MVar [ConnPool Host] } -- master at head after a refresh
newConnPool poolSize' repset = liftIO (newSetConnPool poolSize' repset)
getPipe = getSetPipe
killPipes ReplicaSetConnection{..} = withMVar currentMembers (mapM_ killPipes)
killPipes ReplicaSetConnPool{..} = withMVar currentMembers (mapM_ killPipes)
replicaSet :: (MonadIO' m) => Connection ReplicaSet -> m ReplicaSet
-- ^ Set name with current members as seed list
replicaSet ReplicaSetConnection{..} = ReplicaSet repsetName . map connHost <$> readMVar currentMembers
instance Show (ConnPool ReplicaSet) where
show r = "ConnPool " ++ show (unsafePerformIO $ replicaSet r)
connectSet :: Int -> ReplicaSet -> IO (Connection ReplicaSet)
-- ^ Create a connection to each member of the replica set.
connectSet poolSize' repset = assert (not . null $ seedHosts repset) $ do
currentMembers <- newMVar =<< mapM (connect poolSize') (seedHosts repset)
return $ ReplicaSetConnection (setName repset) currentMembers
replicaSet :: (MonadIO' m) => ConnPool ReplicaSet -> m ReplicaSet
-- ^ Return replicas set name with current members as seed list
replicaSet ReplicaSetConnPool{..} = ReplicaSet repsetName . map connHost <$> readMVar currentMembers
getMembers :: Name -> [Connection Host] -> ErrorT IOError IO [Host]
newSetConnPool :: Int -> ReplicaSet -> IO (ConnPool ReplicaSet)
-- ^ Create a connection pool to each member of the replica set.
newSetConnPool poolSize' repset = assert (not . null $ seedHosts repset) $ do
currentMembers <- newMVar =<< mapM (newConnPool poolSize') (seedHosts repset)
return $ ReplicaSetConnPool (setName repset) currentMembers
getMembers :: Name -> [ConnPool Host] -> ErrorT IOError IO [Host]
-- ^ Get members of replica set, master first. Query supplied connections until config found.
-- TODO: Verify config for request replica set name and not some other replica set. ismaster config should include replica set name in result but currently does not.
getMembers _repsetName connections = hosts <$> untilSuccess (getReplicaInfo <=< getHostPipe) connections
refreshMembers :: Name -> [Connection Host] -> ErrorT IOError IO [Connection Host]
refreshMembers :: Name -> [ConnPool Host] -> ErrorT IOError IO [ConnPool Host]
-- ^ Update current members with master at head. Reuse unchanged members. Throw IOError if can't connect to any and fetch config. Dropped connections are not closed in case they still have users; they will be closed when garbage collected.
refreshMembers repsetName connections = do
n <- liftIO . poolSize . connPool $ head connections
mapM (connection n) =<< getMembers repsetName connections
where
connection n host' = maybe (connect n host') return $ find ((host' ==) . connHost) connections
connection n host' = maybe (newConnPool n host') return $ find ((host' ==) . connHost) connections
getSetPipe :: MasterOrSlaveOk -> Connection ReplicaSet -> ErrorT IOError IO Pipe
getSetPipe :: MasterOrSlaveOk -> ConnPool ReplicaSet -> ErrorT IOError IO Pipe
-- ^ Return a pipe to primary or a random secondary in replica set. Use primary for SlaveOk if and only if no secondaries. Note, refreshes members each time (makes ismaster call to primary).
getSetPipe mos ReplicaSetConnection{..} = modifyMVar currentMembers $ \conns -> do
getSetPipe mos ReplicaSetConnPool{..} = modifyMVar currentMembers $ \conns -> do
connections <- refreshMembers repsetName conns -- master at head after refresh
pipe <- case mos of
Master -> getHostPipe (head connections)

2
Database/MongoDB/Internal/Protocol.hs
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@ -42,7 +42,7 @@ import Control.Monad.Error
-- * Pipe
type Pipe = P.Pipeline Handle ByteString
-- ^ Thread-safe TCP connection to server with pipelined requests
-- ^ Thread-safe TCP connection with pipelined requests
mkPipe :: Handle -> IO Pipe
-- ^ New thread-safe pipelined connection over handle

8
Database/MongoDB/Internal/Util.hs
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@ -1,4 +1,4 @@
-- | Miscellaneous general functions
-- | Miscellaneous general functions and Show, Eq, and Ord instances for PortID
{-# LANGUAGE StandaloneDeriving #-}
@ -14,12 +14,6 @@ deriving instance Show PortID
deriving instance Eq PortID
deriving instance Ord PortID
snoc :: [a] -> a -> [a]
-- ^ add element to end of list (/snoc/ is reverse of /cons/, which adds to front of list)
snoc list a = list ++ [a]
type Secs = Float
bitOr :: (Bits a) => [a] -> a
-- ^ bit-or all numbers together
bitOr = foldl (.|.) 0

51
Database/MongoDB/Query.hs
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@ -1,4 +1,4 @@
-- | Query and update documents residing on a MongoDB server(s)
-- | Query and update documents
{-# LANGUAGE OverloadedStrings, RecordWildCards, NamedFieldPuns, TupleSections, FlexibleContexts, FlexibleInstances, UndecidableInstances, MultiParamTypeClasses, GeneralizedNewtypeDeriving, StandaloneDeriving, TypeSynonymInstances, RankNTypes, ImpredicativeTypes #-}
@ -24,7 +24,7 @@ module Database.MongoDB.Query (
-- ** Delete
delete, deleteOne,
-- * Read
slaveOk,
readMode,
-- ** Query
Query(..), QueryOption(..), Projector, Limit, Order, BatchSize,
explain, find, findOne, count, distinct,
@ -62,23 +62,12 @@ import Database.MongoDB.Internal.Util ((<.>), true1)
mapErrorIO :: (Throw e m, MonadIO m) => (e' -> e) -> ErrorT e' IO a -> m a
mapErrorIO f = throwLeft' f . liftIO . runErrorT
send :: (Context Pipe m, Throw Failure m, MonadIO m) => [Notice] -> m ()
-- ^ Send notices as a contiguous batch to server with no reply. Throw 'ConnectionFailure' if pipe fails.
send ns = mapErrorIO ConnectionFailure . flip P.send ns =<< context
call :: (Context Pipe m, Throw Failure m, MonadIO m) => [Notice] -> Request -> m (forall n. (Throw Failure n, MonadIO n) => n Reply)
-- ^ Send notices and request as a contiguous batch to server and return reply promise, which will block when invoked until reply arrives. This call will throw 'ConnectionFailure' if pipe fails on send, and promise will throw 'ConnectionFailure' if pipe fails on receive.
call ns r = do
pipe <- context
promise <- mapErrorIO ConnectionFailure (P.call pipe ns r)
return (mapErrorIO ConnectionFailure promise)
-- * Mongo Monad
access :: (Server s, MonadIO m) => WriteMode -> MasterOrSlaveOk -> Connection s -> Action m a -> m (Either Failure a)
-- ^ Run action with access to server or replica set via one of the 'Pipe's (TCP connections) in given 'Connection' pool
access w mos conn act = do
ePipe <- liftIO . runErrorT $ getPipe mos conn
access :: (Server s, MonadIO m) => WriteMode -> MasterOrSlaveOk -> ConnPool s -> Action m a -> m (Either Failure a)
-- ^ Run action under given write and read mode against the server or replicaSet behind given connection pool. Return Left Failure if there is a connection failure or read/write error.
access w mos pool act = do
ePipe <- liftIO . runErrorT $ getPipe mos pool
either (return . Left . ConnectionFailure) (runAction act w mos) ePipe
-- | A monad with access to a 'Pipe', 'MasterOrSlaveOk', and 'WriteMode', and throws 'Failure' on read, write, or pipe failure
@ -93,10 +82,11 @@ instance MonadTrans Action where
lift = Action . lift . lift . lift . lift
runAction :: Action m a -> WriteMode -> MasterOrSlaveOk -> Pipe -> m (Either Failure a)
-- ^ Run action with access to pipe. It starts out assuming it is master (invoke 'slaveOk' inside it to change that) and that writes don't need to be check (invoke 'writeMode' to change that). Return Left Failure if error in execution. Throws IOError if pipe fails during execution.
-- ^ Run action with given write mode and read mode (master or slave-ok) against given pipe (TCP connection). Return Left Failure if read/write error or connection failure.
-- 'access' calls runAction. Use this directly if you want to use the same connection and not take from the pool again. However, the connection may still be used by other threads at the same time. For instance, the pool will still hand this connection out.
runAction (Action action) w mos = runReaderT (runReaderT (runReaderT (runErrorT action) w) mos)
-- | Read or write exception like cursor expired or inserting a duplicate key.
-- | A connection failure, or a read or write exception like cursor expired or inserting a duplicate key.
-- Note, unexpected data from the server is not a Failure, rather it is a programming error (you should call 'error' in this case) because the client and server are incompatible and requires a programming change.
data Failure =
ConnectionFailure IOError -- ^ TCP connection ('Pipe') failed. Make work if you try again on the same Mongo 'Connection' which will create a new Pipe.
@ -115,7 +105,7 @@ newtype Database = Database {databaseName :: UString} deriving (Eq, Ord)
instance Show Database where show (Database x) = unpack x
-- | As 'Access' monad with access to a particular 'Database'
-- | 'Access' monad with a particular 'Database' in context
class (Context Database m, Access m) => DbAccess m
instance (Context Database m, Access m) => DbAccess m
@ -124,7 +114,7 @@ allDatabases :: (Access m) => m [Database]
allDatabases = map (Database . at "name") . at "databases" <$> use (Database "admin") (runCommand1 "listDatabases")
use :: Database -> ReaderT Database m a -> m a
-- ^ Run Db action against given database
-- ^ Run action against given database
use = flip runReaderT
thisDatabase :: (DbAccess m) => m Database
@ -297,9 +287,9 @@ delete' opts (Select sel col) = do
-- ** MasterOrSlaveOk
slaveOk :: (Access m) => m a -> m a
-- ^ Ok to execute given action against slave, ie. eventually consistent reads
slaveOk = push (const SlaveOk)
readMode :: (Access m) => MasterOrSlaveOk -> m a -> m a
-- ^ Execute action using given read mode. Master = consistent reads, SlaveOk = eventually consistent reads.
readMode = push . const
msOption :: MasterOrSlaveOk -> [P.QueryOption]
msOption Master = []
@ -619,6 +609,19 @@ eval :: (DbAccess m) => Javascript -> m Document
-- ^ Run code on server
eval code = at "retval" <$> runCommand ["$eval" =: code]
-- * Primitives
send :: (Context Pipe m, Throw Failure m, MonadIO m) => [Notice] -> m ()
-- ^ Send notices as a contiguous batch to server with no reply. Throw 'ConnectionFailure' if pipe fails.
send ns = mapErrorIO ConnectionFailure . flip P.send ns =<< context
call :: (Context Pipe m, Throw Failure m, MonadIO m) => [Notice] -> Request -> m (forall n. (Throw Failure n, MonadIO n) => n Reply)
-- ^ Send notices and request as a contiguous batch to server and return reply promise, which will block when invoked until reply arrives. This call will throw 'ConnectionFailure' if pipe fails on send, and promise will throw 'ConnectionFailure' if pipe fails on receive.
call ns r = do
pipe <- context
promise <- mapErrorIO ConnectionFailure (P.call pipe ns r)
return (mapErrorIO ConnectionFailure promise)
{- Authors: Tony Hannan <tony@10gen.com>
Copyright 2010 10gen Inc.

5
Var/Pool.hs
View file

@ -10,6 +10,7 @@ import Data.Array.IO
import Data.Maybe (catMaybes)
import Control.Monad.Error
import System.Random (randomRIO)
import Control.Exception (assert)
-- | Creator, destroyer, and checker of resources of type r. Creator may throw error or type e.
data Factory e r = Factory {
@ -18,8 +19,8 @@ data Factory e r = Factory {
isExpired :: r -> IO Bool }
newPool :: Factory e r -> Int -> IO (Pool e r)
-- ^ Create new pool of initial max size
newPool f n = do
-- ^ Create new pool of initial max size, which must be >= 1
newPool f n = assert (n > 0) $ do
arr <- newArray (0, n-1) Nothing
var <- newMVar arr
return (Pool f var)

2
mongoDB.cabal
View file

@ -23,7 +23,7 @@ homepage: http://github.com/TonyGen/mongoDB-haskell
package-url:
bug-reports:
synopsis: A driver for MongoDB
description: This module lets you connect to MongoDB, do inserts, queries, updates, etc.
description: This module lets you connect to MongoDB (www.mongodb.org) and do inserts, queries, updates, etc.
category: Database
author: Scott Parish <srp@srparish.net> & Tony Hannan <tony@10gen.com>
tested-with:

80
tutorial.md
View file

@ -1,15 +1,11 @@
MongoDB Haskell Mini Tutorial
-----------------------------
__Author:__ Brian Gianforcaro (b.gianfo@gmail.com)
__Updated:__ 2/28/2010
__Updated:__ Oct 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
[pymongo tutorial](http://api.mongodb.org/python/1.4%2B/tutorial.html).
You will need the mongoDB driver installed as well as mongo itself installed.
of the Haskell mongoDB drivers. You will need the mongoDB driver
installed as well as mongo itself. Prompts used in this tutorial are:
$ = command line prompt
> = ghci repl prompt
@ -18,22 +14,22 @@ You will need the mongoDB driver installed as well as mongo itself installed.
Installing Haskell Bindings
---------------------------
From Hackage using cabal:
$ cabal install mongoDB
From Source:
$ git clone git://github.com/srp/mongoDB.git
$ git clone git://github.com/TonyGen/mongoDB-haskell.git mongoDB
$ 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:
Start a MongoDB instance for us to play with in a separate terminal window:
$ mongod --dbpath <directory where Mongo will store the data>
@ -41,7 +37,7 @@ Start up a haskell repl:
$ ghci
Now we'll need to bring in the MongoDB/Bson bindings and set
Import the MongoDB driver library, and set
OverloadedStrings so literal strings are converted to UTF-8 automatically.
> import Database.MongoDB
@ -49,43 +45,43 @@ OverloadedStrings so literal strings are converted to UTF-8 automatically.
Making A Connection
-------------------
Open up a connection to your mongo server, using the standard port (27017):
Create a connection pool for your mongo server, using the standard port (27017):
> conn <- connect 1 $ host "127.0.0.1"
> pool <- newConnPool 1 $ host "127.0.0.1"
or for a non-standard port
> conn <- connect 1 $ Host "127.0.0.1" (PortNumber 30000)
> pool <- newConnPool 1 $ Host "127.0.0.1" (PortNumber 30000)
*connect* takes the connection pool size and the host to connect to. It returns
a *Connection*, which is really a pool of TCP connections, initially created on demand.
So it is not possible to get a connection error until you try to use it.
*newConnPool* takes the connection pool size and the host to connect to. It returns
a *ConnPool*, which is a potential pool of TCP connections. They are not created until first
access, so it is not possible to get a connection error here.
Plain IO code in this driver never raises an exception unless it invokes third party IO
Note, plain IO code in this driver never raises an exception unless it invokes third party IO
code that does. Driver code that may throw an exception says so in its Monad type,
for example, *ErrorT IOError IO a*.
Access monad
-------------------
A mongo query/update executes in an *Access* monad, which has access to a
*Pipe*, *WriteMode*, and *MasterSlaveOk* mode, and may throw a *Failure*. A Pipe
is a single TCP connection, while a Connection is a pool of Pipes.
A query/update executes in an *Access* monad, which has access to a
*Pipe*, *WriteMode*, and read-mode (*MasterSlaveOk*), and may throw a *Failure*.
A Pipe is a single TCP connection.
To run an Access action (monad), supply WriteMode, MasterOrSlaveOk, Connection,
and action to *access*. For example, to get a list of all the database on the server:
> access safe Master conn allDatabases
*access* return either Left Failure or Right result. Failure means there was a connection failure
or a read or write exception like cursor expired or duplicate key insert.
Since we are working in ghci, which requires us to start from the
IO monad every time, we'll define a convenient *run* function that takes an
action and executes it against our "test" database on the server we
just connected to:
just connected to, with typical write and read mode:
> let run action = access safe Master conn $ use (Database "test") action
*access* return either Left Failure or Right result. Failure means there was a connection failure,
or a read or write exception like cursor expired or duplicate key insert.
> let run action = access safe Master pool $ use (Database "test") action
*use* adds a *Database* to the action context, so query/update operations know which
database to operate on.
@ -96,7 +92,7 @@ Databases and Collections
MongoDB can store multiple databases -- separate namespaces
under which collections reside.
You can obtain the list of databases available on a connection:
As before, you can obtain the list of databases available on a connection:
> run allDatabases
@ -104,12 +100,10 @@ The "test" database in context is ignored in this case because *allDatabases*
is not a query on a specific database but on the server as a whole.
Databases and collections do not need to be created, just start using
them and MongoDB will automatically create them for you.
them and MongoDB will automatically create them for you. In the below examples
we'll be using the database "test" (captured in *run* above) and the colllection "posts".
In the below examples we'll be using the database "test" (captured in *run*
above) and the colllection "posts":
You can obtain a list of collections available in the "test" database:
You can obtain a list of all collections in the "test" database:
> run allCollections
@ -117,9 +111,8 @@ Documents
---------
Data in MongoDB is represented (and stored) using JSON-style
documents. In mongoDB we use the BSON *Document* type to represent
these documents. A document is simply a list of *Field*s, where each field is
a named value. A value is a basic type like Bool, Int, Float, String, Time;
documents, called BSON documents. A *Document" is simply a list of *Field*s,
where each field is a named value. A *Value" is a basic type like Bool, Int, Float, String, Time;
a special BSON value like Binary, Javascript, ObjectId; a (embedded)
Document; or a list of values. Here's an example document which could
represent a blog post:
@ -152,7 +145,7 @@ collections in our database:
> run allCollections
* Note The system.indexes collection is a special internal collection
Note, the system.indexes collection is a special internal collection
that was created automatically.
Getting a single document with findOne
@ -168,8 +161,7 @@ collection:
> run $ findOne (select [] "posts")
The result is a document matching the one that we inserted previously.
* Note: The returned document contains an *_id*, which was automatically
Note, the returned document contains the *_id* field, which was automatically
added on insert.
*findOne* also supports querying on specific elements that the
@ -214,7 +206,7 @@ Querying for More Than One Document
------------------------------------
To get more than a single document as the result of a query we use the
*find* method. *find* returns a cursor instance, which allows us to
*find* method. *find* returns a *Cursor*, which allows us to
iterate over all matching documents. There are several ways in which
we can iterate: we can call *next* to get documents one at a time
or we can get all the results by applying the cursor to *rest*:
@ -226,7 +218,7 @@ Of course you can use bind (*>>=*) to combine these into one line:
> run $ find (select ["author" =: "Mike"] "posts") >>= rest
* Note: *next* automatically closes the cursor when the last
Note, *next* automatically closes the cursor when the last
document has been read out of it. Similarly, *rest* automatically
closes the cursor after returning all the results.
@ -241,7 +233,7 @@ Or count how many documents match a query:
> run $ count (select ["author" =: "Mike"] "posts")
Range Queries
Advanced Queries
-------------
To do