| Safe Haskell | None | 
|---|---|
| Language | Haskell2010 | 
Database.Persist.ImplicitIdDef
Description
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
The Type
data ImplicitIdDef #
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 BackendKey yourBackendTypeSqlBackend 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 UserIdNow, you can simply create an ImplicitIdDef that corresponds to this
 declaration.
newtype UUID = UUIDByteStringinstancePersistFieldUUID wheretoPersistValue(UUID bs) =PersistLiteral_EscapedbsfromPersistValuepv = case pv of PersistLiteral_ Escaped bs -> Right (UUID bs) _ -> Left "nope" instancePersistFieldSqlUUID wheresqlType_ =SqlOtherUUID
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
Arguments
| :: (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 #
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 #
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 #
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