| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
Opaleye.Field
Contents
Description
Functions for working directly with Field_s.
Please note that numeric Field_ types are instances of Num, so
you can use *, /, +, - on them. To create Field_s, see
Opaleye.ToFields and Opaleye.SqlTypes.
Field_ used to be called Field_ and for technical reasons
there are still a few uses of the old name around. If you see
Field_ SqlTypeField
SqlTypeField_ (Nullability SqlType)FieldNullable SqlType
Field_ will be removed in version 0.11.
Synopsis
- data Field_ (n :: Nullability) sqlType
- type Field = Field_ NonNullable
- type FieldNullable = Field_ 'Nullable
- data Nullability
- unsafeCast :: String -> Field_ n a -> Field_ n b
- unsafeCoerceField :: Field_ n a -> Field_ n' b
- null :: FieldNullable a
- isNull :: FieldNullable a -> Field PGBool
- matchNullable :: Field b -> (Field a -> Field b) -> FieldNullable a -> Field b
- fromNullable :: Field a -> FieldNullable a -> Field a
- toNullable :: Field a -> FieldNullable a
- maybeToNullable :: Maybe (Field a) -> FieldNullable a
Documentation
data Field_ (n :: Nullability) sqlType Source #
A field of a Select, of type sqlType. For example a Field
SqlInt4 is an int4 column and a Field SqlText is a text
column.
Instances
type Field = Field_ NonNullable Source #
type FieldNullable = Field_ 'Nullable Source #
data Nullability Source #
Constructors
| NonNullable | |
| Nullable |
Instances
| type A ('H HT :: Arr Type (C Type) Type) ('C '(h, o, N) :: C Type) Source # | |
| type A ('H NullsT :: Arr Type (C Type) Type) ('C '(h, o, n) :: C Type) Source # | |
| type A ('H OT :: Arr Type (C Type) Type) ('C '(h, o, N) :: C Type) Source # | |
| type A ('H OT :: Arr Type (C Type) Type) ('C '(h, o, NN) :: C Type) Source # | |
| type A ('H HT :: Arr Type (C k2) k2) ('C '(h, o, NN) :: C k2) Source # | |
| type A ('H WT :: Arr Type (TC a) Type) ('TC '(t, Opt) :: TC a) Source # | |
| type A ('H HT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) Source # | |
| type A ('H NullsT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) Source # | |
| type A ('H OT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) Source # | |
| type A ('H WT :: Arr Type (TC a) k2) ('TC '(t, Req) :: TC a) Source # | |
Casting fields
unsafeCast :: String -> Field_ n a -> Field_ n b Source #
Cast a column to any other type. Implements Postgres's :: or
CAST( ... AS ... ) operations. This is safe for some
conversions, such as uuid to text.
unsafeCoerceField :: Field_ n a -> Field_ n' b Source #
Working with NULL
Instead of working with NULL you are recommended to use
Opaleye.MaybeFields instead.
null :: FieldNullable a Source #
A NULL of any type
isNull :: FieldNullable a -> Field PGBool Source #
TRUE if the value of the field is NULL, FALSE otherwise.
Arguments
| :: Field b | |
| -> (Field a -> Field b) | |
| -> FieldNullable a | ͘ |
| -> Field b |
If the Field 'Nullable a is NULL then return the Field
'NonNullable b otherwise map the underlying Field 'Nullable a
using the provided function.
The Opaleye equivalent of maybe.
Arguments
| :: Field a | |
| -> FieldNullable a | ͘ |
| -> Field a |
If the FieldNullable a is NULL then return the provided
Field a otherwise return the underlying Field
a.
The Opaleye equivalent of fromMaybe and very similar
to PostgreSQL's COALESCE.
toNullable :: Field a -> FieldNullable a Source #
Treat a field as though it were nullable. This is always safe.
The Opaleye equivalent of Just.
maybeToNullable :: Maybe (Field a) -> FieldNullable a Source #
If the argument is Nothing return NULL otherwise return the
provided value coerced to a nullable type.