Another point: I'm trying to use a `select 1 from....

# komapper

[dave08]

Another point: I'm trying to use a select 1 from... as a column (with a Boolean value), I tried defining:

private fun literalOne(): ScalarExpression<Boolean, Int> {
        val name = "literalOne"
        return columnExpression(Boolean::class, Int::class, { it > 0 },  name, listOf()) {
            append("1")
        } as ScalarExpression<Boolean, Int>
    }

but it seems like a ScalarExpression can't be defined... so I can't use a subquery with select(literalOne()) like this as a column value... is there any way to work around this?

[Toshihiro Nakamura]

Could you tell me what kind of SQL you want to generate?
Is this not the query you are looking for?

QueryDsl.select(literal(true))

[dave08]

I think what I'm looking for is a columnexpression exists(subquery)

[dave08]

That returns a boolean

[dave08]

and the subquery is select 1 ....

[dave08]

which is a scalar subquery, but it doesn't seem I can define custom scalar subqueries currently

[dave08]

QueryDsl.select(literal(true)) is considered a scalar subquery, and if so, all that would be left is to make an exists function for it to appear in select(...)

[dave08]

SELECT foo, EXISTS(select 1 from bar where baz = foo) as isInBar) from fooTable

[dave08]

I guess there's no way to do this @Toshihiro Nakamura?

[Toshihiro Nakamura]

If you want to use the EXISTS operator in the SELECT clause, you can define it like this.

private fun exists(expression: SubqueryExpression<*>): ColumnExpression<Boolean, Boolean> {
    val name = "exists"
    val operand = Operand.Subquery(expression)
    return columnExpression(Boolean::class,  name, listOf(operand)) {
        append("$name(")
        visit(operand)
        append(")")
    }
}

You can use the above function as follows:

val subquery = QueryDsl.select(literal(1))
QueryDsl.from(e).select(exists(subquery))