Database.Selda.Unsafe

Unsafe operations giving the user unchecked low-level control over the generated SQL.

Documentation

fun :: Text -> Col s a -> Col s b

A unary operation. Note that the provided function name is spliced directly into the resulting SQL query. Thus, this function should ONLY be used to implement well-defined functions that are missing from Selda's standard library, and NOT in an ad hoc manner during queries.

fun2 :: Text -> Col s a -> Col s b -> Col s c

Like fun, but with two arguments.

fun0 :: Text -> Col s a

Like fun, but with zero arguments.

operator :: Text -> Col s a -> Col s b -> Col s c

A custom operator. operator "~>" a b will compile down to a ~> b, with parentheses around a and b iff they are not atomic. This means that SQL operator precedence is disregarded, as all subexpressions are parenthesized. In the following example for instance, foo a b c will compile down to (a ~> b) ~> c.

(~>) = operator "~>"
infixl 5 ~>
foo a b c = a ~> b ~> c

aggr :: SqlType a => Text -> Col s a -> Aggr s b

Create a named aggregate function. Like fun, this function is generally unsafe and should ONLY be used to implement missing backend-specific functionality.

cast :: forall s a b. SqlType b => Col s a -> Col s b

Cast a column to another type, using whichever coercion semantics are used by the underlying SQL implementation.

castAggr :: forall s a b. SqlType b => Aggr s a -> Aggr s b

Cast an aggregate to another type, using whichever coercion semantics are used by the underlying SQL implementation.

sink :: (f s a -> f s b) -> f (Inner s) a -> f (Inner s) b

Sink the given function into an inner scope.

Be careful not to use this function with functions capturing rows or columns from an outer scope. For instance, the following usage will likely lead to disaster:

query $ do
  x <- #age `from` select person
  inner $ sink (\p -> x + (p ! #age)) <$> select person

Really, if you have to use this function, ONLY do so in the global scope.

sink2 :: (f s a -> f s b -> f s c) -> f (Inner s) a -> f (Inner s) b -> f (Inner s) c

Like sink, but with two arguments.

unsafeSelector :: (SqlRow a, SqlType b) => Int -> Selector a b

A selector indicating the nth (zero-based) column of a table.

Will cause errors in queries during compilation, execution, or both, unless handled with extreme care. You really shouldn't use it at all.