Database.Relational.Query.Expr

This module defines phantom typed SQL expression object. Contains normal interfaces.

Typed SQL Expression

data Expr p a

Phantom typed SQL expression object. Project from projection type p.

Instances

ProjectableMaybe (Expr p)

Control phantom Maybe type in SQL expression type Expr.

ProjectableShowSql (Expr p)

Unsafely get SQL term from Expr.

SqlProjectable (Expr p)

Unsafely make Expr from SQL terms.

Show (Expr p a)

Show expression.

valueExpr :: ShowConstantTermsSQL ft => ft -> Expr p ft

Typed constant SQL expression from Haskell value.

Type conversion

just :: Expr p ft -> Expr p (Maybe ft)

Convert phantom type into Maybe.

fromJust :: Expr p (Maybe ft) -> Expr p ft

Allowed only for having or where Expr. So NULL expression result will be possible. Behavior around boolean is strongly dependent on RDBMS impelemetations.

exprAnd :: Expr p Bool -> Expr p Bool -> Expr p Bool

AND operator for Expr.