postgresql-simple-0.3.3.0: Mid-Level PostgreSQL client library

Portabilityportable
Stabilityexperimental
MaintainerLeon P Smith <leon@melding-monads.com>
Safe HaskellNone

Database.PostgreSQL.Simple.Types

Description

Basic types.

Synopsis

Documentation

data Null Source

A placeholder for the SQL NULL value.

Constructors

Null 

Instances

Eq Null 
Read Null 
Show Null 
Typeable Null 
ToField Null 
FromField Null

compatible with any data type, but the value must be null

newtype Only a Source

A single-value "collection".

This is useful if you need to supply a single parameter to a SQL query, or extract a single column from a SQL result.

Parameter example:

query c "select x from scores where x > ?" (Only (42::Int))

Result example:

xs <- query_ c "select id from users"
forM_ xs $ \(Only id) -> {- ... -}

Constructors

Only 

Fields

fromOnly :: a
 

Instances

Functor Only 
Typeable1 Only 
Eq a => Eq (Only a) 
Ord a => Ord (Only a) 
Read a => Read (Only a) 
Show a => Show (Only a) 
ToField a => ToRow (Only a) 
FromField a => FromRow (Only a) 

newtype In a Source

Wrap a list of values for use in an IN clause. Replaces a single "?" character with a parenthesized list of rendered values.

Example:

 query c "select * from whatever where id in ?" (Only (In [3,4,5]))

Constructors

In a 

Instances

Functor In 
Typeable1 In 
Eq a => Eq (In a) 
Ord a => Ord (In a) 
Read a => Read (In a) 
Show a => Show (In a) 
ToField a => ToField (In [a]) 

newtype Binary a Source

Wrap binary data for use as a bytea value.

Constructors

Binary a 

newtype Query Source

A query string. This type is intended to make it difficult to construct a SQL query by concatenating string fragments, as that is an extremely common way to accidentally introduce SQL injection vulnerabilities into an application.

This type is an instance of IsString, so the easiest way to construct a query is to enable the OverloadedStrings language extension and then simply write the query in double quotes.

 {-# LANGUAGE OverloadedStrings #-}

 import Database.PostgreSQL.Simple

 q :: Query
 q = "select ?"

The underlying type is a ByteString, and literal Haskell strings that contain Unicode characters will be correctly transformed to UTF-8.

Constructors

Query 

newtype Oid

Constructors

Oid CUInt 

data h :. t Source

A composite type to parse your custom data structures without having to define dummy newtype wrappers every time.

 instance FromRow MyData where ...
 instance FromRow MyData2 where ...

then I can do the following for free:

 res <- query' c ...
 forM res $ \(MyData{..} :. MyData2{..}) -> do
   ....

Constructors

h :. t 

Instances

Typeable2 :. 
(Eq h, Eq t) => Eq (:. h t) 
(Ord h, Ord t) => Ord (:. h t) 
(Read h, Read t) => Read (:. h t) 
(Show h, Show t) => Show (:. h t) 
(ToRow a, ToRow b) => ToRow (:. a b) 
(FromRow a, FromRow b) => FromRow (:. a b)