Database.Cassandra.JSON

A higher level module for working with Cassandra.

Row and Column keys can be any string-like type implementing the CKey typeclass. You can add your own types by defining new instances

Serialization and de-serialization of Column values are taken care of automatically using the ToJSON and FromJSON typeclasses.

Also, this module currently attempts to reduce verbosity by throwing errors instead of returning Either types as in the Database.Cassandra.Basic module.

Connection

type CPool = Pool Cassandra Server

A round-robin pool of cassandra connections

type Server = (HostName, PortID)

defServer :: Server

A localhost server with default configuration

defServers :: [Server]

A single localhost server with default configuration

type KeySpace = String

createCassandraPool

Arguments

:: [Server]

List of servers to connect to

-> Int

Max connections per server (n)

-> NominalDiffTime

Kill each connection after this many seconds

-> KeySpace

Each pool operates on a single KeySpace

-> IO CPool

Create a pool of connections to a cluster of Cassandra boxes

Each box in the cluster will get up to n connections. The pool will send queries in round-robin fashion to balance load on each box in the cluster.

Necessary Types

class CKey a where

A typeclass to enable using any string-like type for row and column keys

Methods

toBS :: a -> ByteString

fromBS :: ByteString -> a

Instances

CKey String

CKey ByteString

CKey Text

CKey ByteString

CKey Text

data ModifyOperation a

Possible outcomes of a modify operation

Constructors

Update a

Delete

DoNothing

Instances

Eq a => Eq (ModifyOperation a)

Ord a => Ord (ModifyOperation a)

Read a => Read (ModifyOperation a)

Show a => Show (ModifyOperation a)

type ColumnFamily = String

data ConsistencyLevel

Constructors

ONE

QUORUM

LOCAL_QUORUM

EACH_QUORUM

ALL

ANY

TWO

THREE

Instances

Enum ConsistencyLevel

Eq ConsistencyLevel

Ord ConsistencyLevel

Show ConsistencyLevel

Typeable ConsistencyLevel

data CassandraException

Constructors

NotFoundException

InvalidRequestException String

UnavailableException

TimedOutException

AuthenticationException String

AuthorizationException String

SchemaDisagreementException

ConversionException String

OperationNotSupported String

Instances

Eq CassandraException

Data CassandraException

Ord CassandraException

Read CassandraException

Show CassandraException

Typeable CassandraException

Exception CassandraException

Cassandra Operations

get :: (CKey rowKey, CKey colKey, FromJSON a) => CPool -> ColumnFamily -> rowKey -> Selector -> ConsistencyLevel -> IO [(colKey, a)]

An arbitrary get operation - slice with Selector.

Internally based on Basic.get. Table is assumed to be a regular ColumnFamily and contents of returned columns are cast into the target type.

getCol :: (CKey rowKey, CKey colKey, FromJSON a) => CPool -> ColumnFamily -> rowKey -> colKey -> ConsistencyLevel -> IO (Maybe a)

Get a single column from a single row

insertCol

Arguments

:: (CKey rowKey, CKey colKey, ToJSON a)

=> CPool

-> ColumnFamily

-> rowKey

-> colKey

-> ConsistencyLevel

-> a

Content

-> IO ()

modify

Arguments

:: (CKey rowKey, CKey colKey, ToJSON a, FromJSON a)

=> CPool

-> ColumnFamily

-> rowKey

-> colKey

-> ConsistencyLevel

Read quorum

-> ConsistencyLevel

Write quorum

-> (Maybe a -> IO (ModifyOperation a, b))

Modification function. Called with Just the value if present, Nothing otherwise.

-> IO b

Return the decided ModifyOperation and its execution outcome

A modify function that will fetch a specific column, apply modification function on it and save results back to Cassandra.

A b side value is returned for computational convenience.

This is intended to be a workhorse function, in that you should be able to do all kinds of relatively straightforward operations just using this function.

This method may throw a CassandraException for all exceptions other than NotFoundException.

modify_

Arguments

:: (CKey rowKey, CKey colKey, ToJSON a, FromJSON a)

=> CPool

-> ColumnFamily

-> rowKey

-> colKey

-> ConsistencyLevel

Read quorum

-> ConsistencyLevel

Write quorum

-> (Maybe a -> IO (ModifyOperation a))

Modification function. Called with Just the value if present, Nothing otherwise.

-> IO ()

Same as modify but does not offer a side value.

This method may throw a CassandraException for all exceptions other than NotFoundException.

delete

Arguments

:: CKey rowKey

=> CPool

Cassandra connection

-> ColumnFamily

In ColumnFamily

-> rowKey

Key to be deleted

-> Selector

Columns to be deleted

-> ConsistencyLevel

-> IO ()

Same as the delete in the Cassandra.Basic module, except that it throws an exception rather than returning an explicit Either value.