. package:hledger-web

Right to left function composition.

(f . g) x = f (g x)

f . id = f = id . f

Examples

>>> map ((*2) . length) [[], [0, 1, 2], [0]]
[0,6,2]

>>> foldr (.) id [(+1), (*3), (^3)] 2
25

>>> let (...) = (.).(.) in ((*2)...(+)) 5 10
30

Retrieve the value associated with the given key of an Object. The result is empty if the key is not present or the value cannot be converted to the desired type. This accessor is appropriate if the key and value must be present in an object for it to be valid. If the key and value are optional, use .:? instead.

Non-equality check.

Examples

selectSimon :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSimon = selectList [UserName !=. "SPJ" ] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

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      |
+-----+-----+--------+

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       |
+-----+-----+---------+

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       |
+-----+-----+---------+

Check if value is not in given list.

Examples

selectSimon :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSimon = selectList [UserAge /<-. [40]] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

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       |
+-----+-----+---------+

Check if value is in given list.

Examples

selectUsers :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectUsers = selectList [UserAge <-. [40, 41]] []

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

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

selectSPJ :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSPJ = selectList [UserAge <-. [40]] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

Less-than check.

Examples

selectLessAge :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectLessAge = selectList [UserAge <. 41 ] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

Less-than or equal check.

Examples

selectLessEqualAge :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectLessEqualAge = selectList [UserAge <=. 40 ] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

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      |
+-----+-----+--------+

Check for equality.

Examples

selectSPJ :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectSPJ = selectList [UserName ==. "SPJ" ] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|1    |SPJ  |40   |
+-----+-----+-----+

Greater-than check.

Examples

selectGreaterAge :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectGreaterAge = selectList [UserAge >. 40 ] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

Greater-than or equal check.

Examples

selectGreaterEqualAge :: MonadIO m => ReaderT SqlBackend m [Entity User]
selectGreaterEqualAge = selectList [UserAge >=. 41 ] []

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

+-----+-----+-----+
|id   |name |age  |
+-----+-----+-----+
|2    |Simon|41   |
+-----+-----+-----+

The OR of two lists of filters. For example:

selectList
([ PersonAge >. 25
, PersonAge <. 30 ] ||.
[ PersonIncome >. 15000
, PersonIncome <. 25000 ])
[]

will filter records where a person's age is between 25 and 30 or a person's income is between (15000 and 25000). If you are looking for an (&&.) operator to do (A AND B AND (C OR D)) you can use the (++) operator instead as there is no (&&.). For example:

selectList
([ PersonAge >. 25
, PersonAge <. 30 ] ++
([PersonCategory ==. 1] ||.
[PersonCategory ==. 5]))
[]

will filter records where a person's age is between 25 and 30 and (person's category is either 1 or 5).