Hi everyone. I'm trying to add a custom function for postgres (the `nullif` function). But I have no...

# exposed

[Gustav Elmgren]

Hi everyone. I'm trying to add a custom function for postgres (the nullif function). But I have no idea what to specify the column type as. Any thoughts?

[Bogdan]

do with generic

[Bogdan]

https://github.com/JetBrains/Exposed/blob/master/exposed-java-time/src/main/kotlin/org/jetbrains/exposed/sql/javatime/JavaDateFunctions.kt#L14

[Gustav Elmgren]

I'm not sure how that would help me. A function requires a column type, but the nullif does not have one I guess?

[Bogdan]

class NullIf<T>(expr: ExpressionWithColumnType<T>, default: Expression<T>) :
    CustomFunction<T>("nullif", expr.columnType, expr, default)

[Bogdan]

or

class NullIf<T>(expr: Expression<T>, default: Expression<T>, columnType: IColumnType) :
    CustomFunction<T>("nullif", columnType, expr, default)

fun <T> nullif(expr: ExpressionWithColumnType<T>, default: Expression<T>): NullIf<T> =
    NullIf(expr, default, expr.columnType)

fun <T> nullif(expr: Expression<T>, default: ExpressionWithColumnType<T>): NullIf<T> =
    NullIf(expr, default, default.columnType)

// optimistic: VarCharColumnType
fun <T> nullif(expr: Expression<T>, default: Expression<T>): NullIf<T> =
    NullIf(expr, default, VarCharColumnType())

[Bogdan]

fun <T> nullif(expr: ExpressionWithColumnType<T>, default: T): NullIf<T> =
    NullIf(expr, QueryParameter(default, expr.columnType), expr.columnType)

[Gustav Elmgren]

Ah, I see. But in the cases where it returns null, it would still think it would be of type T, which cant be null?

[Bogdan]

Yes. Need a question mark

[Bogdan]

fun <T> nullif(expr: ExpressionWithColumnType<T>, default: T): NullIf<T?> =

[Bogdan]

+-

[Bogdan]

I showed an example. Experiment with generics to get the results you want

[Gustav Elmgren]

I see. Thanks!!