persistent-2.13.3.5: Type-safe, multi-backend data serialization.
Safe Haskell None
Language Haskell2010

Database.Persist.Types

Description

This module exports many types and functions for operating on persistent 's database representation. It's a bit of a kitchen sink. In the future, this module will be reorganized, and many of the dependent modules will be viewable on their own for easier documentation and organization.

Synopsis

Various Types of Names

There are so many kinds of names. persistent defines newtype wrappers for Text so you don't confuse what a name is and what it is supposed to be used for

Database Definitions

Entity/Table Definitions

The EntityDef type is used by persistent to generate Haskell code, generate database migrations, and maintain metadata about entities. These are generated in the call to mkPersist .

Field definitions

The FieldDef type is used to describe how a field should be represented at the Haskell and database layers.

Intermediate Values

The PersistValue type is used as an intermediate layer between database and Haskell types.

Other Useful Stuff

data Update record Source #

Updating a database entity.

Persistent users use combinators to create these.

type family BackendSpecificUpdate backend record Source #

data SelectOpt record Source #

Query options.

Persistent users use these directly.

Constructors

forall typ. Asc ( EntityField record typ)
forall typ. Desc ( EntityField record typ)
OffsetBy Int
LimitTo Int

data Filter record Source #

Filters which are available for select , updateWhere and deleteWhere . Each filter constructor specifies the field being filtered on, the type of comparison applied (equals, not equals, etc) and the argument for the comparison.

Persistent users use combinators to create these.

Note that it's important to be careful about the PersistFilter that you are using, if you use this directly. For example, using the In PersistFilter requires that you have an array- or list-shaped EntityField . It is possible to construct values using this that will create malformed runtime values.

Constructors

forall typ. PersistField typ => Filter
FilterAnd [ Filter record]

convenient for internal use, not needed for the API

FilterOr [ Filter record]
BackendFilter ( BackendSpecificFilter ( PersistEntityBackend record) record)

data FilterValue typ where Source #

Value to filter with. Highly dependant on the type of filter used.

Since: 2.10.0

Constructors

FilterValue :: typ -> FilterValue typ
FilterValues :: [typ] -> FilterValue typ
UnsafeValue :: forall a typ. PersistField a => a -> FilterValue typ

type family BackendSpecificFilter backend record Source #

data family Key record Source #

By default, a backend will automatically generate the key Instead you can specify a Primary key made up of unique values.

data Entity record Source #

Datatype that represents an entity, with both its Key and its Haskell record representation.

When using a SQL-based backend (such as SQLite or PostgreSQL), an Entity may take any number of columns depending on how many fields it has. In order to reconstruct your entity on the Haskell side, persistent needs all of your entity columns and in the right order. Note that you don't need to worry about this when using persistent 's API since everything is handled correctly behind the scenes.

However, if you want to issue a raw SQL command that returns an Entity , then you have to be careful with the column order. While you could use SELECT Entity.* WHERE ... and that would work most of the time, there are times when the order of the columns on your database is different from the order that persistent expects (for example, if you add a new field in the middle of you entity definition and then use the migration code -- persistent will expect the column to be in the middle, but your DBMS will put it as the last column). So, instead of using a query like the one above, you may use rawSql (from the Database.Persist.GenericSql module) with its /entity selection placeholder/ (a double question mark ?? ). Using rawSql the query above must be written as SELECT ?? WHERE .. . Then rawSql will replace ?? with the list of all columns that we need from your entity in the right order. If your query returns two entities (i.e. (Entity backend a, Entity backend b) ), then you must you use SELECT ??, ?? WHERE ... , and so on.

Constructors

Entity

Fields

Instances

Instances details
( Eq ( Key record), Eq record) => Eq ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

( Ord ( Key record), Ord record) => Ord ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

( Read ( Key record), Read record) => Read ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

( Show ( Key record), Show record) => Show ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

( Generic ( Key record), Generic record) => Generic ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

Associated Types

type Rep ( Entity record) :: Type -> Type Source #

( PersistEntity record, PersistField record, PersistField ( Key record)) => PersistField ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

( PersistField record, PersistEntity record) => PersistFieldSql ( Entity record) Source #
Instance details

Defined in Database.Persist.Sql.Class

( PersistEntity record, PersistEntityBackend record ~ backend, IsPersistBackend backend) => RawSql ( Entity record) Source #
Instance details

Defined in Database.Persist.Sql.Class

type Rep ( Entity record) Source #
Instance details

Defined in Database.Persist.Class.PersistEntity

type Rep ( Entity record) = D1 (' MetaData "Entity" "Database.Persist.Class.PersistEntity" "persistent-2.13.3.5-AzqyBkRvmH2EfWG2peHu6H" ' False ) ( C1 (' MetaCons "Entity" ' PrefixI ' True ) ( S1 (' MetaSel (' Just "entityKey") ' NoSourceUnpackedness ' NoSourceStrictness ' DecidedLazy ) ( Rec0 ( Key record)) :*: S1 (' MetaSel (' Just "entityVal") ' NoSourceUnpackedness ' NoSourceStrictness ' DecidedLazy ) ( Rec0 record)))

newtype OverflowNatural Source #

Prior to persistent-2.11.0 , we provided an instance of PersistField for the Natural type. This was in error, because Natural represents an infinite value, and databases don't have reasonable types for this.

The instance for Natural used the Int64 underlying type, which will cause underflow and overflow errors. This type has the exact same code in the instances, and will work seamlessly.

A more appropriate type for this is the Word series of types from Data.Word . These have a bounded size, are guaranteed to be non-negative, and are quite efficient for the database to store.

Since: 2.11.0

Instances

Instances details
Eq OverflowNatural Source #
Instance details

Defined in Database.Persist.Class.PersistField

Num OverflowNatural Source #
Instance details

Defined in Database.Persist.Class.PersistField

Ord OverflowNatural Source #
Instance details

Defined in Database.Persist.Class.PersistField

Show OverflowNatural Source #
Instance details

Defined in Database.Persist.Class.PersistField

PersistField OverflowNatural Source #
Instance details

Defined in Database.Persist.Class.PersistField

PersistFieldSql OverflowNatural Source #

This type uses the SqlInt64 version, which will exhibit overflow and underflow behavior. Additionally, it permits negative values in the database, which isn't ideal.

Since: 2.11.0

Instance details

Defined in Database.Persist.Sql.Class

The rest of the types

data LiteralType Source #

A type that determines how a backend should handle the literal.

Since: 2.12.0.0

Constructors

Escaped

The accompanying value will be escaped before inserting into the database. This is the correct default choice to use.

Since: 2.12.0.0

Unescaped

The accompanying value will not be escaped when inserting into the database. This is potentially dangerous - use this with care.

Since: 2.12.0.0

DbSpecific

The DbSpecific constructor corresponds to the legacy PersistDbSpecific constructor. We need to keep this around because old databases may have serialized JSON representations that reference this. We don't want to break the ability of a database to load rows.

Since: 2.12.0.0

data PersistValue Source #

A raw value which can be stored in any backend and can be marshalled to and from a PersistField .

Constructors

PersistText Text
PersistByteString ByteString
PersistInt64 Int64
PersistDouble Double
PersistRational Rational
PersistBool Bool
PersistDay Day
PersistTimeOfDay TimeOfDay
PersistUTCTime UTCTime
PersistNull
PersistList [ PersistValue ]
PersistMap [( Text , PersistValue )]
PersistObjectId ByteString

Intended especially for MongoDB backend

PersistArray [ PersistValue ]

Intended especially for PostgreSQL backend for text arrays

PersistLiteral_ LiteralType ByteString

This constructor is used to specify some raw literal value for the backend. The LiteralType value specifies how the value should be escaped. This can be used to make special, custom types avaialable in the back end.

Since: 2.12.0.0

Bundled Patterns

pattern PersistDbSpecific :: ByteString -> PersistValue

Deprecated: Deprecated since 2.11 because of inconsistent escaping behavior across backends. The Postgres backend escapes these values, while the MySQL backend does not. If you are using this, please switch to PersistLiteral_ and provide a relevant LiteralType for your conversion.

This pattern synonym used to be a data constructor for the PersistValue type. It was changed to be a pattern so that JSON-encoded database values could be parsed into their corresponding values. You should not use this, and instead prefer to pattern match on PersistLiteral_ directly.

If you use this, it will overlap a patern match on the 'PersistLiteral_, PersistLiteral , and PersistLiteralEscaped patterns. If you need to disambiguate between these constructors, pattern match on PersistLiteral_ directly.

Since: 2.12.0.0

pattern PersistLiteral :: ByteString -> PersistValue

This pattern synonym used to be a data constructor on PersistValue , but was changed into a catch-all pattern synonym to allow backwards compatiblity with database types. See the documentation on PersistDbSpecific for more details.

Since: 2.12.0.0

pattern PersistLiteralEscaped :: ByteString -> PersistValue

This pattern synonym used to be a data constructor on PersistValue , but was changed into a catch-all pattern synonym to allow backwards compatiblity with database types. See the documentation on PersistDbSpecific for more details.

Since: 2.12.0.0

Instances

Instances details
Eq PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

Ord PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

Read PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

Show PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

ToJSON PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

FromJSON PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

ToHttpApiData PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

FromHttpApiData PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

PathPiece PersistValue Source #
Instance details

Defined in Database.Persist.PersistValue

PersistField PersistValue Source #
Instance details

Defined in Database.Persist.Class.PersistField

PersistFieldSql PersistValue Source #
Instance details

Defined in Database.Persist.Sql.Class

data FieldDef Source #

A FieldDef represents the inormation that persistent knows about a field of a datatype. This includes information used to parse the field out of the database and what the field corresponds to.

Constructors

FieldDef

Fields

data SqlType Source #

A SQL data type. Naming attempts to reflect the underlying Haskell datatypes, eg SqlString instead of SqlVarchar. Different SQL databases may have different translations for these types.

data CascadeAction Source #

An action that might happen on a deletion or update on a foreign key change.

Since: 2.11.0

data FieldCascade Source #

This datatype describes how a foreign reference field cascades deletes or updates.

This type is used in both parsing the model definitions and performing migrations. A Nothing in either of the field values means that the user has not specified a CascadeAction . An unspecified CascadeAction is defaulted to Restrict when doing migrations.

Since: 2.11.0

data ForeignDef Source #

type ForeignFieldDef = ( FieldNameHS , FieldNameDB ) Source #

Used instead of FieldDef to generate a smaller amount of code

data CompositeDef Source #

data UniqueDef Source #

Type for storing the Uniqueness constraint in the Schema. Assume you have the following schema with a uniqueness constraint:

Person
  name String
  age Int
  UniqueAge age

This will be represented as:

UniqueDef
    { uniqueHaskell = ConstraintNameHS (packPTH UniqueAge)
    , uniqueDBName = ConstraintNameDB (packPTH "unique_age")
    , uniqueFields = [(FieldNameHS (packPTH "age"), FieldNameDB (packPTH "age"))]
    , uniqueAttrs = []
    }

data EmbedFieldDef Source #

An EmbedFieldDef is the same as a FieldDef But it is only used for embeddedFields so it only has data needed for embedding

data EmbedEntityDef Source #

An EmbedEntityDef is the same as an EntityDef But it is only used for fieldReference so it only has data needed for embedding

data ReferenceDef Source #

There are 3 kinds of references 1) composite (to fields that exist in the record) 2) single field 3) embedded

Constructors

NoReference
ForeignRef ! EntityNameHS

A ForeignRef has a late binding to the EntityDef it references via name and has the Haskell type of the foreign key in the form of FieldType

EmbedRef EntityNameHS
CompositeRef CompositeDef
SelfReference

A SelfReference stops an immediate cycle which causes non-termination at compile-time (issue #311).

data FieldType Source #

A FieldType describes a field parsed from the QuasiQuoter and is used to determine the Haskell type in the generated code.

name Text parses into FTTypeCon Nothing Text

name T.Text parses into FTTypeCon (Just T Text )

name (Jsonb User) parses into:

FTApp (FTTypeCon Nothing Jsonb) (FTTypeCon Nothing User)

data FieldAttr Source #

Attributes that may be attached to fields that can affect migrations and serialization in backend-specific ways.

While we endeavor to, we can't forsee all use cases for all backends, and so FieldAttr is extensible through its constructor FieldAttrOther .

Since: 2.11.0.0

Constructors

FieldAttrMaybe

The Maybe keyword goes after the type. This indicates that the column is nullable, and the generated Haskell code will have a Maybe type for it.

Example:

User
    name Text Maybe
FieldAttrNullable

This indicates that the column is nullable, but should not have a Maybe type. For this to work out, you need to ensure that the PersistField instance for the type in question can support a PersistNull value.

data What = NoWhat | Hello Text

instance PersistField What where
    fromPersistValue PersistNull =
        pure NoWhat
    fromPersistValue pv =
        Hello $ fromPersistValue pv

instance PersistFieldSql What where
    sqlType _ = SqlString

User
    what What nullable
FieldAttrMigrationOnly

This tag means that the column will not be present on the Haskell code, but will not be removed from the database. Useful to deprecate fields in phases.

You should set the column to be nullable in the database. Otherwise, inserts won't have values.

User
    oldName Text MigrationOnly
    newName Text
FieldAttrSafeToRemove

A SafeToRemove attribute is not present on the Haskell datatype, and the backend migrations should attempt to drop the column without triggering any unsafe migration warnings.

Useful after you've used MigrationOnly to remove a column from the database in phases.

User
    oldName Text SafeToRemove
    newName Text
FieldAttrNoreference

This attribute indicates that we should create a foreign key reference from a column. By default, persistent will try and create a foreign key reference for a column if it can determine that the type of the column is a Key entity or an EntityId and the Entity 's name was present in mkPersist .

This is useful if you want to use the explicit foreign key syntax.

Post
    title    Text

Comment
    postId   PostId      noreference
    Foreign Post fk_comment_post postId
FieldAttrReference Text

This is set to specify precisely the database table the column refers to.

Post
    title    Text

Comment
    postId   PostId references="post"

You should not need this - persistent should be capable of correctly determining the target table's name. If you do need this, please file an issue describing why.

FieldAttrConstraint Text

Specify a name for the constraint on the foreign key reference for this table.

Post
    title    Text

Comment
    postId   PostId constraint="my_cool_constraint_name"
FieldAttrDefault Text

Specify the default value for a column.

User
    createdAt    UTCTime     default="NOW()"

Note that a default= attribute does not mean you can omit the value while inserting.

FieldAttrSqltype Text

Specify a custom SQL type for the column. Generally, you should define a custom datatype with a custom PersistFieldSql instance instead of using this.

User
    uuid     Text    sqltype=UUID
FieldAttrMaxlen Integer

Set a maximum length for a column. Useful for VARCHAR and indexes.

User
    name     Text    maxlen=200

    UniqueName name
FieldAttrSql Text

Specify the database name of the column.

User
    blarghle     Int     sql="b_l_a_r_g_h_l_e"

Useful for performing phased migrations, where one column is renamed to another column over time.

FieldAttrOther Text

A grab bag of random attributes that were unrecognized by the parser.

data WhyNullable Source #

The reason why a field is nullable is very important. A field that is nullable because of a Maybe tag will have its type changed from A to Maybe A . OTOH, a field that is nullable because of a nullable tag will remain with the same type.

data Checkmark Source #

A Checkmark should be used as a field type whenever a uniqueness constraint should guarantee that a certain kind of record may appear at most once, but other kinds of records may appear any number of times.

NOTE: You need to mark any Checkmark fields as nullable (see the following example).

For example, suppose there's a Location entity that represents where a user has lived:

Location
    user    UserId
    name    Text
    current Checkmark nullable

    UniqueLocation user current

The UniqueLocation constraint allows any number of Inactive Location s to be current . However, there may be at most one current Location per user (i.e., either zero or one per user).

This data type works because of the way that SQL treats NULL able fields within uniqueness constraints. The SQL standard says that NULL values should be considered different, so we represent Inactive as SQL NULL , thus allowing any number of Inactive records. On the other hand, we represent Active as TRUE , so the uniqueness constraint will disallow more than one Active record.

Note: There may be DBMSs that do not respect the SQL standard's treatment of NULL values on uniqueness constraints, please check if this data type works before relying on it.

The SQL BOOLEAN type is used because it's the smallest data type available. Note that we never use FALSE , just TRUE and NULL . Provides the same behavior Maybe () would if () was a valid PersistField .

Constructors

Active

When used on a uniqueness constraint, there may be at most one Active record.

Inactive

When used on a uniqueness constraint, there may be any number of Inactive records.

Instances

Instances details
Bounded Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

Enum Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

Eq Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

Ord Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

Read Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

Show Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

ToHttpApiData Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

FromHttpApiData Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

PathPiece Checkmark Source #
Instance details

Defined in Database.Persist.Types.Base

PersistField Checkmark Source #
Instance details

Defined in Database.Persist.Class.PersistField

PersistFieldSql Checkmark Source #
Instance details

Defined in Database.Persist.Sql.Class

keyAndEntityFields :: EntityDef -> NonEmpty FieldDef Source #

Returns a NonEmpty list of FieldDef that correspond with the key columns for an EntityDef .

parseFieldAttrs :: [ Text ] -> [ FieldAttr ] Source #

Parse raw field attributes into structured form. Any unrecognized attributes will be preserved, identically as they are encountered, as FieldAttrOther values.

Since: 2.11.0.0

noCascade :: FieldCascade Source #

A FieldCascade that does nothing.

Since: 2.11.0