| Portability | non-portable |
|---|---|
| Stability | experimental |
| Maintainer | haskelldb-users@lists.sourceforge.net |
Database.HaskellDB.FieldType
Description
Defines the types of database columns, and functions for converting these between HSQL and internal formats
- type FieldDesc = (FieldType, Bool)
- data FieldType
- toHaskellType :: FieldType -> String
- class ExprType e where
- fromHaskellType :: e -> FieldDesc
- class ExprTypes r where
- fromHaskellTypes :: r -> [FieldDesc]
- queryFields :: (ShowLabels r, ExprTypes r) => Query (Rel r) -> [(String, FieldDesc)]
Documentation
data FieldType
A database column type
toHaskellType :: FieldType -> String
class ExprType e where
Class which retrieves a field description from a given type. Instances are provided for most concrete types. Instances for Maybe automatically make the field nullable, and instances for all (Expr a) types where a has an ExprType instance allows type information to be recovered from a given column expression.
Methods
fromHaskellType :: e -> FieldDesc
class ExprTypes r where
Class which returns a list of field descriptions. Gets the descriptions of all columns in a Record/query. Most useful when the columns associated with each field in a (Rel r) type must be recovered. Note that this occurs at the type level only and no values are inspected.
Methods
fromHaskellTypes :: r -> [FieldDesc]
queryFields :: (ShowLabels r, ExprTypes r) => Query (Rel r) -> [(String, FieldDesc)]
Given a query, returns a list of the field names and their types used by the query. Useful for recovering field information once a query has been built up.