Database.Persist

This defines the API for performing database actions. There are two levels to this API: dealing with fields, and dealing with entities. In SQL, a field corresponds to a column, and should be a single, non-composite value. An entity corresponds to a SQL table. In other words: An entity is a collection of fields.

Fields

data PersistValue

A raw value which can be stored in any backend and can be marshalled to and from a PersistField.

Constructors

PersistString String

PersistByteString ByteString

PersistInt64 Int64

PersistDouble Double

PersistBool Bool

PersistDay Day

PersistTimeOfDay TimeOfDay

PersistUTCTime UTCTime

PersistNull

Instances

Eq PersistValue

Read PersistValue

Show PersistValue

Typeable PersistValue

data SqlType

A SQL data type. Naming attempts to reflect the underlying Haskell datatypes, eg SqlString instead of SqlVarchar. Different SQL databases may have different translations for these types.

Constructors

SqlString

SqlInteger

SqlReal

SqlBool

SqlDay

SqlTime

SqlDayTime

SqlBlob

Instances

Eq SqlType

Read SqlType

Show SqlType

Typeable SqlType

class PersistField a where

A value which can be marshalled to and from a PersistValue.

Methods

toPersistValue :: a -> PersistValue

fromPersistValue :: PersistValue -> Either String a

sqlType :: a -> SqlType

isNullable :: a -> Bool

Instances

PersistField Bool

PersistField Double

PersistField Int

PersistField Int64

PersistField String

PersistField ByteString

PersistField Text

PersistField TimeOfDay

PersistField UTCTime

PersistField Day

PersistField SomePersistField

PersistField a => PersistField (Maybe a)

PersistField (Html ())

Entities

class PersistEntity val where

A single database entity. For example, if writing a blog application, a blog entry would be an entry, containing fields such as title and content.

Associated Types

type PersistMonad val :: (* -> *) -> * -> *

The monad transformer in which actions for this entity must occur. For example, entities declared to work with a sqlite backend would most likely use a ReaderT monad transformer holding onto a database connection.

By using a monad transformer here, users can allow arbitrary effects to exist in the underlying monad. For example, Yesod applications can embed a Handler monad here. The only restriction on that underlying monad is it must be an instance of MonadCatchIO.

data Key val

The unique identifier associated with this entity. In general, backends also define a type synonym for this, such that "type MyEntityId = Key MyEntity".

data Update val

Fields which can be updated using the update and updateWhere functions.

data Filter val

Filters which are available for select, updateWhere and deleteWhere. Each filter constructor specifies the field being filtered on, the type of comparison applied (equals, not equals, etc) and the argument for the comparison.

data Order val

How you can sort the results of a select.

data Unique val

Unique keys in existence on this entity.

Methods

initialize :: MonadCatchIO m => val -> PersistMonad val m ()

Prepare database for this entity, if necessary. In SQL, this creates values and indices if they don't exist. The first argument is not used, so you can used undefined.

insert :: MonadCatchIO m => val -> PersistMonad val m (Key val)

Create a new record in the database, returning the newly created identifier.

replace :: MonadCatchIO m => Key val -> val -> PersistMonad val m ()

Replace the record in the database with the given key. Result is undefined if such a record does not exist.

update :: MonadCatchIO m => Key val -> [Update val] -> PersistMonad val m ()

Update individual fields on a specific record.

updateWhere :: MonadCatchIO m => [Filter val] -> [Update val] -> PersistMonad val m ()

Update individual fields on any record matching the given criterion.

delete :: MonadCatchIO m => Key val -> PersistMonad val m ()

Delete a specific record by identifier. Does nothing if record does not exist.

deleteBy :: MonadCatchIO m => Unique val -> PersistMonad val m ()

Delete a specific record by unique key. Does nothing if no record matches.

deleteWhere :: MonadCatchIO m => [Filter val] -> PersistMonad val m ()

Delete all records matching the given criterion.

get :: MonadCatchIO m => Key val -> PersistMonad val m (Maybe val)

Get a record by identifier, if available.

getBy :: MonadCatchIO m => Unique val -> PersistMonad val m (Maybe (Key val, val))

Get a record by unique key, if available. Returns also the identifier.

select :: MonadCatchIO m => [Filter val] -> [Order val] -> PersistMonad val m [(Key val, val)]

Get all records matching the given criterion in the specified order. Returns also the identifiers.