Database.Persist.Sql.Lifted.Update

Type

data Update record

Updating a database entity.

Persistent users use combinators to create these.

Basic update

(=.) :: forall v typ. PersistField typ => EntityField v typ -> typ -> Update v infixr 3

Assign a field a value.

Examples

updateAge :: MonadIO m => ReaderT SqlBackend m ()
updateAge = updateWhere [UserName ==. "SPJ" ] [UserAge =. 45]

Similar to updateWhere which is shown in the above example you can use other functions present in the module Database.Persist.Class. Note that the first parameter of updateWhere is [Filter val] and second parameter is [Update val]. By comparing this with the type of ==. and =., you can see that they match up in the above usage.

The above query when applied on dataset-1, will produce this:

+-----+-----+--------+
|id   |name |age     |
+-----+-----+--------+
|1    |SPJ  |40 -> 45|
+-----+-----+--------+
|2    |Simon|41      |
+-----+-----+--------+

Arithmetic update

(+=.) :: forall v typ. PersistField typ => EntityField v typ -> typ -> Update v infixr 3

Assign a field by addition (+=).

Examples

addAge :: MonadIO m => ReaderT SqlBackend m ()
addAge = updateWhere [UserName ==. "SPJ" ] [UserAge +=. 1]

The above query when applied on dataset-1, will produce this:

+-----+-----+---------+
|id   |name |age      |
+-----+-----+---------+
|1    |SPJ  |40 -> 41 |
+-----+-----+---------+
|2    |Simon|41       |
+-----+-----+---------+

(-=.) :: forall v typ. PersistField typ => EntityField v typ -> typ -> Update v infixr 3

Assign a field by subtraction (-=).

Examples

subtractAge :: MonadIO m => ReaderT SqlBackend m ()
subtractAge = updateWhere [UserName ==. "SPJ" ] [UserAge -=. 1]

The above query when applied on dataset-1, will produce this:

+-----+-----+---------+
|id   |name |age      |
+-----+-----+---------+
|1    |SPJ  |40 -> 39 |
+-----+-----+---------+
|2    |Simon|41       |
+-----+-----+---------+

(*=.) :: forall v typ. PersistField typ => EntityField v typ -> typ -> Update v infixr 3

Assign a field by multiplication (*=).

Examples

multiplyAge :: MonadIO m => ReaderT SqlBackend m ()
multiplyAge = updateWhere [UserName ==. "SPJ" ] [UserAge *=. 2]

The above query when applied on dataset-1, will produce this:

+-----+-----+--------+
|id   |name |age     |
+-----+-----+--------+
|1    |SPJ  |40 -> 80|
+-----+-----+--------+
|2    |Simon|41      |
+-----+-----+--------+

(/=.) :: forall v typ. PersistField typ => EntityField v typ -> typ -> Update v infixr 3

Assign a field by division (/=).

Examples

divideAge :: MonadIO m => ReaderT SqlBackend m ()
divideAge = updateWhere [UserName ==. "SPJ" ] [UserAge /=. 2]

The above query when applied on dataset-1, will produce this:

+-----+-----+---------+
|id   |name |age      |
+-----+-----+---------+
|1    |SPJ  |40 -> 20 |
+-----+-----+---------+
|2    |Simon|41       |
+-----+-----+---------+