Safe Haskell | None |
---|---|
Language | Haskell2010 |
This module contains types and functions for creating an
ImplicitIdDef
,
which allows you to customize the implied ID column that
persistent
generates.
If this module doesn't suit your needs, you may want to import Database.Persist.ImplicitIdDef.Internal instead. If you do so, please file an issue on GitHub so we can support your needs. Breaking changes to that module will *not* be accompanied with a major version bump.
Since: 2.13.0.0
Synopsis
- data ImplicitIdDef
- mkImplicitIdDef :: forall t. ( Typeable t, PersistFieldSql t) => Text -> ImplicitIdDef
- autoIncrementingInteger :: ImplicitIdDef
- setImplicitIdDefMaxLen :: Integer -> ImplicitIdDef -> ImplicitIdDef
- unsafeClearDefaultImplicitId :: ImplicitIdDef -> ImplicitIdDef
The Type
data ImplicitIdDef Source #
A specification for how the implied ID columns are created.
By default,
persistent
will give each table a default column named
id
(customizable by
PersistSettings
), and the column type will be whatever
you'd expect from
. For The
BackendKey
yourBackendType
SqlBackend
type,
this is an auto incrementing integer primary key.
You might want to give a different example. A common use case in postgresql is to use the UUID type, and automatically generate them using a SQL function.
Previously, you'd need to add a custom
Id
annotation for each model.
User Id UUID default="uuid_generate_v1mc()" name Text Dog Id UUID default="uuid_generate_v1mc()" name Text user UserId
Now, you can simply create an
ImplicitIdDef
that corresponds to this
declaration.
newtype UUID = UUIDByteString
instancePersistField
UUID wheretoPersistValue
(UUID bs) =PersistLiteral_
Escaped
bsfromPersistValue
pv = case pv of PersistLiteral_ Escaped bs -> Right (UUID bs) _ -> Left "nope" instancePersistFieldSql
UUID wheresqlType
_ =SqlOther
UUID
With this instance at the ready, we can now create our implicit definition:
uuidDef :: ImplicitIdDef uuidDef = mkImplicitIdDef @UUID "uuid_generate_v1mc()"
And we can use
setImplicitIdDef
to use this with the
MkPersistSettings
for our block.
mkPersist (setImplicitIdDef uuidDef sqlSettings) [persistLowerCase| ... |]
TODO: either explain interaction with mkMigrate or fix it. see issue #1249 for more details.
Since: 2.13.0.0
Construction
:: forall t. ( Typeable t, PersistFieldSql t) | |
=> Text |
The default expression to use for columns. Should be valid SQL in the language you're using. |
-> ImplicitIdDef |
Create an
ImplicitIdDef
based on the
Typeable
and
PersistFieldSql
constraints in scope.
This function uses the
TypeApplications
syntax. Let's look at an example
that works with Postgres UUIDs.
newtype UUID = UUID Text deriving newtype PersistField instance PersistFieldSql UUID where sqlType _ = SqlOther "UUID" idDef :: ImplicitIdDef idDef = mkImplicitIdDefTypeable @UUID "uuid_generate_v1mc()"
This
ImplicitIdDef
will generate default UUID columns, and the database
will call the
uuid_generate_v1mc()
function to generate the value for new
rows being inserted.
If the type
t
is
Text
or
String
then a
max_len
attribute of 200 is
set. To customize this, use
setImplicitIdDefMaxLen
.
Since: 2.13.0.0
Autoincrementing Integer Key
autoIncrementingInteger :: ImplicitIdDef Source #
This is the default variant. Setting the implicit ID definition to this value should not have any change at all on how entities are defined by default.
Since: 2.13.0.0
Getters
Setters
setImplicitIdDefMaxLen :: Integer -> ImplicitIdDef -> ImplicitIdDef Source #
Set the maximum length of the implied ID column. This is required for
any type where the associated
SqlType
is a
TEXT
or
VARCHAR
sort of
thing.
Since: 2.13.0.0
unsafeClearDefaultImplicitId :: ImplicitIdDef -> ImplicitIdDef Source #
Remove the default attribute of the
ImplicitIdDef
column. This will
require you to provide an ID for the model with every insert, using
insertKey
instead of
insert
, unless the type has some means of getting
around that in the migrations.
As an example, the Postgresql
SERIAL
type expands to an autoincrementing
integer. Postgres will implicitly create the relevant series and set the
default to be
NEXTVAL(
. A default is therefore unnecessary to
use for this type.
series_name
)
However, for a
UUID
, postgres *does not* have an implicit default. You must
either specify a default UUID generation function, or insert them yourself
(again, using
insertKey
).
This function will be deprecated in the future when omiting the default implicit ID column is more fully supported.
Since: 2.13.0.0