Documentation

IS NULL comparison.

For IS NOT NULL, you can negate this with not_, as in not_ (isNothing (person ^. PersonAge))

Warning: Persistent and Esqueleto have different behavior for != Nothing:

In SQL, = NULL and != NULL return NULL instead of true or false. For this reason, you very likely do not want to use !=. Nothing in Esqueleto. You may find these hlint rules helpful to enforce this:

- error: {lhs: v Database.Esqueleto.==. Database.Esqueleto.nothing, rhs: Database.Esqueleto.isNothing v, name: Use Esqueleto's isNothing}
- error: {lhs: v Database.Esqueleto.==. Database.Esqueleto.val Nothing, rhs: Database.Esqueleto.isNothing v, name: Use Esqueleto's isNothing}
- error: {lhs: v Database.Esqueleto.!=. Database.Esqueleto.nothing, rhs: not_ (Database.Esqueleto.isNothing v), name: Use Esqueleto's not isNothing}
- error: {lhs: v Database.Esqueleto.!=. Database.Esqueleto.val Nothing, rhs: not_ (Database.Esqueleto.isNothing v), name: Use Esqueleto's not isNothing}

An alias for isNothing that avoids clashing with the function from Data.Maybe isNothing.

Since: esqueleto-3.5.10.0

Analogous to Just, promotes a value of type typ into one of type Maybe typ. It should hold that val . Just === just . val.

This function will try not to produce a nested Maybe. This is in accord with how SQL represents NULL. That means that just . just = just. This behavior was changed in v3.6.0.0. If you want to produce nested Maybe, see just'.

NULL value.

Join nested Maybes in a Value into one. This is useful when calling aggregate functions on nullable fields.

As of v3.6.0.0, this function will attempt to work on both SqlExpr (Value (Maybe a)) as well as SqlExpr (Value (Maybe (Maybe a))) inputs to make transitioning to NullableFieldProjection easier. This may make type inference worse in some cases. If you want the monomorphic variant, see joinV'

COALESCE function. Evaluates the arguments in order and returns the value of the first non-NULL SqlExpression, or NULL (Nothing) otherwise. Some RDBMSs (such as SQLite) require at least two arguments; please refer to the appropriate documentation.

Since: esqueleto-1.4.3

Like coalesce, but takes a non-nullable SqlExpression placed at the end of the SqlExpression list, which guarantees a non-NULL result.

Since: esqueleto-1.4.3