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资源说明：High level Cassandra bindings for Haskell
# cassy - Haskell Cassandra Client [](https://travis-ci.org/Soostone/cassy)
## Introduction
The intent is to develop a high quality, high level driver similar to
pycassa.
## API Documentation
Please see the Haddocks hosted on HackageDB:
http://hackage.haskell.org/package/cassy
## Examples
### Database.Cassandra.Basic Usage
This module offers low-level functionality that is still much
more pleasant than using Thrift directly.
import Database.Cassandra.Basic
test :: IO ()
test = do
pool <- createCassandraPool defServers 3 300 "TestKeySpace"
insert pool "testCF" "key1" QUORUM [col "col1" "value1"]
getCol pool "testCF" "key1" "col1" QUORUM
### Database.Cassandra.Marshall Usage
This is the primary high level functionality module. Its use is
recommended above the other options.
- Columns can be any Haskell type with a CasType instance. See
`Database.Cassandra.Pack` for what you can use there out of the box.
- You can choose how to encode/decode your column content. Out of the
box, we support Show/Read, ToJSON/FromJSON, Serialize and SafeCopy.
Example usage: JSON-encoded columns
import Database.Cassandra.Marshall
import Data.Aeson
type Name = String
type Age = Int
data Person = Person Name Age
-- Define JSON serialization for our data structure
instance ToJSON Person where
toJSON (Person nm age) = toJSON (nm,age)
instance FromJSON Person where
parseJSON v = do
(nm, age) <- parseJSON v
return $ Person nm age
test :: Person -> IO ()
test p@(Person nm age) = do
pool <- createCassandraPool defServers 3 300 "TestKeySpace"
-- I can use any string-like key and don't have to explicitly
-- convert person to ByteString.
runCas pool $ insertCol casJSON "testCF" "people" nm QUORUM p
-- Automatically de-serialized back to a datatype
res <- runCas pool $ getCol casJSON "testCF" "people" nm QUORUM
case res of
Just (Person nm age) -> return age
Nothing -> error "Oh NO!!!"
## Release Notes
### Version 0.7
* We now use retry >= 0.4 and hence exceptions machinery instead of
monad-control.
### Version 0.6
* Updated to work with monad-control instead of MonadCatchIO.
* Now using retry >= 0.3 for the same reason.
* More CasType instances in Pack module for completeness. Preference
is shifting to using native Haskell types directly.
* `Database.Cassandra.JSON` module is now formally deprecated and will
be removed in 0.7. Please switch to `Marshall`, which can replace it
in entirety.
### Version 0.5
* Added `Database.Cassandra.Marshall` that is now intended to be the
primary module to be used in all Cassandra operations. This module
supercedes and replaces the `Database.Cassandra.JSON` high level
module. Building on top of the Basic module, Marshall allows user to
pick the serialization methodology for each of the operations. We
provide out of box support for JSON, cereal, safecopy and plain old
show/read.
* A new `TTimeStamp` type makes it easier to have timestamps as
Long-encoded columns.
* There is now simple support for pagination of columns in wide rows,
CPS-style. See the `paginate` function in
`Database.Cassandra.Marshall`.
* Numerous other fixes and tweaks
### Version 0.4
This version packs a fairly large changeset. It will almost definitely
break your code, although the fix/adjustment is likely to be minor.
* Vastly enhanced the Database.Cassandra.Pack module to represent
types that Cassandra can sort and validate.
* Added CasType typeclass that offers `encodeCas` and `decodeCas`
methods that handle conversions to/from the binary ByteString
representation.
* Composite columns are now supported through tuples. Just pick two or
more CasType instances and put them in a tuple to automatically
trigger composite column conversion. Keep in mind that your
ColumnFamily schema must be configured right or else you'll get
runtime exceptions.
* Added a bunch of newtype wrappers to directly map to types Cassandra
knows. These include `TAscii`, `TBytes`, `TInt`, `TUtf8` and some
others.
* Changed several methods in Basic and JSON modules to expect CasType
column key values instead of concrete ByteString.
* Added the useful `packCol` and `unpackCol` functions to smoothly
handle column key type conversions when working with the Basic
module.
* Made the Cas monad a simple type synonym for ReaderT CPool.
* Added the `get_` metho to `JSON` to make it easier to discard key
names and just get the column contents.
* Numerous fixes and minor tweaks.
### Version 0.3
* Added MonadCassandra typeclass, which is now used by *all*
operations by default.
* Added a default Cas moand that instantiates MonadCassandra for
convenience.
* All Basic module ops now return results directly instead of an
Either wrapper. Each operation may raise a CassandraException.
* Connection pooling now builds on top of the resource-pool library to
initiate connections to multiple servers in round-robin fashion.
* Basic.insert now knows how to insert a SuperColumn.
## TODOs
* Add support for counters and batch mutators
* Add support for database/admin operations
## Contributions
Would love to get contributions, bug reports, suggestions, feedback
from the community.
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