Safe Haskell	None
Language	Haskell2010

Hasql.Backend

Contents

Connection
Results
Statements
Mapping
Transaction

Description

An open API for implementation of specific backend drivers.

Synopsis

Connection

class Cx c where Source

Associated Types

type CxSettings c Source

Connection settings.

type CxError c Source

A connection acquisition error.

Methods

acquireCx :: CxSettings c -> IO (Either (CxError c) c) Source

releaseCx :: c -> IO () Source

Results

data family ResultValue c Source

A raw value returned from the database.

type ResultRow c = Vector (ResultValue c) Source

A raw result row.

type ResultStream c = ListT IO (ResultRow c) Source

A stream of rows of a result.

type ResultMatrix c = Vector (ResultRow c) Source

A matrix of a result.

Statements

data Stmt c Source

A statement template packed with its values and settings.

Constructors

Stmt
Fields stmtTemplate :: !Text stmtParams :: !(Vector (StmtParam c)) stmtPreparable :: !Bool

data family StmtParam c Source

A prepared statement parameter.

Mapping

class CxValue c v where Source

A support by a backend of mapping a specific data type.

Methods

encodeValue :: v -> StmtParam c Source

decodeValue :: ResultValue c -> Either Text v Source

Transaction

class CxTx c where Source

A transaction execution support.

Associated Types

type TxError c Source

A transaction error.

Methods

runTx :: c -> TxMode -> Tx c a -> IO (Either (TxError c) (Maybe a)) Source

Given an established connection execute a transaction, returning either an error or a maybe result, in which a Nothing indicates that the transaction should be retried.

data TxIsolationLevel Source

For reference see the Wikipedia info.

Constructors

RepeatableReads
Serializable
ReadCommitted
ReadUncommitted

type TxMode = Maybe (TxIsolationLevel, TxWriteMode) Source

A mode, defining how a transaction should be executed.

Just (isolationLevel, write) indicates that a database transaction should be established with a specified isolation level and a write mode.
Nothing indicates that there should be no database transaction established on the backend and therefore it should be executed with no ACID guarantees, but also without any induced overhead.

type TxWriteMode = Maybe Bool Source

Nothing indicates a "read" mode.
Just True indicates a "write" mode.
Just False indicates a "write" mode without committing. This is useful for testing, allowing you to modify your database, producing some result based on your changes, and to let Hasql roll all the changes back on the exit from the transaction.

type Tx c = FreeT (TxF c) (MaybeT (EitherT (TxError c) IO)) Source

data TxF c x Source

Constructors

UnitTx (Stmt c) x
CountTx (Stmt c) (Word64 -> x)
VectorTx (Stmt c) (Vector (ResultRow c) -> x)
StreamTx (Stmt c) (ListT (Tx c) (ResultRow c) -> x)

Instances

Functor (TxF c)

unitTx :: Stmt c -> Tx c () Source

countTx :: Stmt c -> Tx c Word64 Source

vectorTx :: Stmt c -> Tx c (Vector (ResultRow c)) Source

streamTx :: Stmt c -> Tx c (ListT (Tx c) (ResultRow c)) Source