fix: EXPOSED-227 Slice() with empty list creates invalid SQL #1899
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Providing an empty list to slice() resulted in a SELECT statement without any columns defined, which returned syntax exceptions in all databases except PostgreSQL and H2 (these returned empty results). Adding require() to the query prepareSQL() allows an early fail in this situation. The check could also go directly in an init block in the Slice class. It could not go directly in the function itself, in the edge case that a user uses Slice directly.
bog-walk
commented
Nov 25, 2023
Comment on lines
+108
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| require(set.fields.isNotEmpty()) { "Can't prepare SELECT statement without columns or expressions to retrieve" } | ||
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The check cannot be placed directly inside the slice() because that would not prevent the edge case of a user creating a Slice instance instead of calling the method (it's odd but is possible):
MyTable.slice(emptyList()).selectAll()
// vs
Slice(MyTable, emptyList()).selectAll()So the alternative location is to put the check inside Slice:
class Slice(override val source: ColumnSet, override val fields: List<Expression<*>>) : FieldSet {
init {
require(fields.isNotEmpty()) { "Can't prepare SELECT statement without columns or expressions to retrieve" }
}
}
e5l
approved these changes
Nov 27, 2023
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Currently providing an empty list to
slice()results in a SELECT statement without any columns defined, which returns syntax exceptions in all databases except PostgreSQL and H2 (these return empty results).Adding a check to
Query.prepareSQL()allows an early fail now.