Safe Haskell	None
Language	Haskell2010

Opaleye.Field

Contents

Coercing fields
Working with NULL

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 Column and for technical reasons there are still a few uses of the old name around. If you see Column SqlType then you can understand it as Field SqlType, and if you see Column (Nullable SqlType) then you can understand it as FieldNullable SqlType.

Column will be fully deprecated in version 0.8.

Synopsis

type family Field_ (a :: Nullability) b
type Field a = Field_ 'NonNullable a
type FieldNullable a = Field_ 'Nullable a
data Nullability
- = NonNullable
- | Nullable
unsafeCoerceField :: Column a -> Column b
null :: FieldNullable a
isNull :: FieldNullable a -> Field PGBool
matchNullable :: Field_ 'NonNullable b -> (Field_ 'NonNullable a -> Field_ 'NonNullable b) -> Field_ 'Nullable a -> Field_ 'NonNullable b
fromNullable :: Field_ 'NonNullable a -> Field_ 'Nullable a -> Field_ 'NonNullable a
toNullable :: Field_ 'NonNullable a -> Field_ 'Nullable a
maybeToNullable :: Maybe (Field_ 'NonNullable a) -> Field_ 'Nullable a

Documentation

type family Field_ (a :: Nullability) b Source #

The name Column will be replaced by Field in version 0.8. The Field_, Field and FieldNullable types exist to help smooth the transition. We recommend that you use Field_, Field or FieldNullable instead of Column everywhere that it is sufficient.

Instances

Instances details

type Field_ 'NonNullable a Source #
Instance details Defined in Opaleye.Field type Field_ 'NonNullable a = Column a
type Field_ 'Nullable a Source #
Instance details Defined in Opaleye.Field type Field_ 'Nullable a = Column (Nullable a)

type Field a = Field_ 'NonNullable a Source #

type FieldNullable a = Field_ 'Nullable a Source #

data Nullability Source #

Constructors

NonNullable
Nullable

Instances

Instances details

type A ('H NullsT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H NullsT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) = A ('H NullsT :: Arr Type (C a) k2) ('C t)
type A ('H WT :: Arr Type (TC a) k2) ('TC '(t, Req) :: TC a) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H WT :: Arr Type (TC a) k2) ('TC '(t, Req) :: TC a) = A ('H OT :: Arr Type (C a) k2) ('C t)
type A ('H OT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H OT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) = A ('H OT :: Arr Type (C a) k2) ('C t)
type A ('H HT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H HT :: Arr Type (TC a) k2) ('TC '(t, b) :: TC a) = A ('H HT :: Arr Type (C a) k2) ('C t)
type A ('H HT :: Arr Type (C k2) k2) ('C '(h, o, NN) :: C k2) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H HT :: Arr Type (C k2) k2) ('C '(h, o, NN) :: C k2) = h
type A ('H WT :: Arr Type (TC a) Type) ('TC '(t, Opt) :: TC a) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H WT :: Arr Type (TC a) Type) ('TC '(t, Opt) :: TC a) = Maybe (A ('H OT :: Arr Type (C a) Type) ('C t))
type A ('H NullsT :: Arr Type (C Type) Type) ('C '(h, o, n) :: C Type) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H NullsT :: Arr Type (C Type) Type) ('C '(h, o, n) :: C Type) = Column (Nullable o)
type A ('H OT :: Arr Type (C Type) Type) ('C '(h, o, N) :: C Type) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H OT :: Arr Type (C Type) Type) ('C '(h, o, N) :: C Type) = Column (Nullable o)
type A ('H OT :: Arr Type (C Type) Type) ('C '(h, o, NN) :: C Type) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H OT :: Arr Type (C Type) Type) ('C '(h, o, NN) :: C Type) = Column o
type A ('H HT :: Arr Type (C Type) Type) ('C '(h, o, N) :: C Type) Source #
Instance details Defined in Opaleye.Internal.TypeFamilies type A ('H HT :: Arr Type (C Type) Type) ('C '(h, o, N) :: C Type) = Maybe h

Coercing fields

unsafeCoerceField :: Column a -> Column 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.

matchNullable Source #

Arguments

:: Field_ 'NonNullable b
-> (Field_ 'NonNullable a -> Field_ 'NonNullable b)
-> Field_ 'Nullable a
-> Field_ 'NonNullable 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.

Will be generalized to Field_ n b in a later version.

fromNullable Source #

Arguments

:: Field_ 'NonNullable a
-> Field_ 'Nullable a
-> Field_ 'NonNullable a

If the Field 'Nullable a is NULL then return the provided Field 'NonNullable a otherwise return the underlying Field 'NonNullable a.

The Opaleye equivalent of fromMaybe and very similar to PostgreSQL's COALESCE.

Will be generalized to Field_ n a in a later version.

toNullable :: Field_ 'NonNullable a -> Field_ 'Nullable a Source #

Treat a field as though it were nullable. This is always safe.

The Opaleye equivalent of Just.

Will be generalized to Field_ n a in a later version.

maybeToNullable :: Maybe (Field_ 'NonNullable a) -> Field_ 'Nullable a Source #

If the argument is Nothing return NULL otherwise return the provided value coerced to a nullable type.

Will be generalized to Maybe (Field_ n a) in a later version.

Documentation

Instances

Instances

Coercing fields

Working with NULL

Working with `NULL`