Contents Index

Dbconnect

Contents Connection Creation Data Manipulation Select Statements Exceptions Tools

Description

Module to connect to a PostgreSQL Database http://www.postgresql.org/

Synopsis

data DBService createDBService :: String -> String -> String -> String -> String -> Maybe String -> DBService execute :: DBService -> QueryString -> IO Int selectReturnTuples :: DBService -> QueryString -> IO [[String]] selectReturnRow :: DBService -> QueryString -> Int -> IO [String] selectReturnList :: DBService -> QueryString -> IO [String] selectReturnOne :: DBService -> QueryString -> IO String catchDB :: IO a -> (DBException -> IO a) -> IO a data DBException = DBError ErrorType String | Exception data ErrorType = ConnectionError | ExecuteError setclause :: String -> String -> String setclausex :: String -> String -> String escapeQuery :: String -> String type QueryString = String

Connection Creation

data DBService

createDBService

:: String database server, either IP-address or servername -> String name of the database to connect with -> String commandline options to be sent to the server -> String user name on server -> String password of the user -> Maybe String Just pathname specifies location of logfile, Nothing selects default "/tmp/dbconnect.log" -> DBService Create an open database handle

Data Manipulation

execute :: DBService -> QueryString -> IO Int

takes a data manipulating statement (insert or update), sends it to the database and returns the number of affected rows

Select Statements

selectReturnTuples :: DBService -> QueryString -> IO [[String]]

Executes a select query, returns the entire result

selectReturnRow :: DBService -> QueryString -> Int -> IO [String]

Executes a select query, returns the ith row

selectReturnList :: DBService -> QueryString -> IO [String]

Executes a select query, returns a list of the first elements of each tuple, the same as do {i <- selectReturnTuples query; return (map head i)}

selectReturnOne :: DBService -> QueryString -> IO String

Executes a select query, returns the first element of the first row, or "" if the result is empty. Useful if the query result is a single value

Exceptions

catchDB :: IO a -> (DBException -> IO a) -> IO a

data DBException

Specifies an Exception which may be thrown by createDBService or any of the DBService functions. Use catchDB to catch this Exception in the main routine. See also: DBConnectExample. Constructors DBError ErrorType String Constructor taking the type of error and a string with a more detailed description Exception Instances Typeable DBException Show DBException

data ErrorType

Specifies the type of an error, so you can do exception handling depending on the type of exception Constructors ConnectionError There's something wrong with the connection: usually the connection is broken ExecuteError There's something wrong with the query: the execution returns an error Instances Typeable ErrorType Show ErrorType

Tools

setclause

:: String columnname -> String value -> String Construct the string: "columname='value' "

setclausex

:: String columnname -> String value -> String Construct the string: "columname='value',"

escapeQuery :: String -> String

Escaping a string. Useful to secure untrustworthy user input in forms

type QueryString = String

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