Hello! I have trouble understanding the coalesce t...

# exposed

[maxmello]

Hello! I have trouble understanding the coalesce type parameter

class Coalesce<out T, S : T?>(
    private val expr: ExpressionWithColumnType<S>,
    private val alternate: Expression<out T>,
    private vararg val others: Expression<out T>
) : Function<S>(expr.columnType)

Shouldn’t it be Function<T>, since T is non-nullable and the point of coalesce is to convert a nullable expression to a non-nullable expression?

[spand]

I dont think SQL has a restriction that it must produce a not null value

[spand]

So how can Exposed?

[spand]

However, the Coalesce could be reworked (afaik) to return the type of the last expression which then could be either nullable or not null and thus give the Coalesce instance a not null type parameter

[maxmello]

That is true, but if I understand correctly, T can be nullable, but S is always nullable, and thus the result from Coalesce is always nullable even if I know it not to be.

In my example, I have implemented concat operator which I want to accept only non-nullable columns/expressions:

(name concatSpaced description concatSpaced author concatSpaced coalesce(publisher, stringLiteral("")).toTsVector()

Here, publisher is nullable, but this would not compile because Coalesce is Function<S> not Function<T>, so I have to cast it to Expression<String> manually

[Chantal Loncle]

Hi @maxmello You're correct and this change was not intended behavior. A fix for this issue is underway. Please track EXPOSED-389 if you're interested.