kosiew commented on code in PR #26156:
URL: https://github.com/apache/datafusion/pull/26156#discussion_r4399629319
##########
datafusion/expr/src/expr_schema.rs:
##########
@@ -1278,6 +1276,54 @@ mod tests {
assert_eq!(expr.metadata(&schema).unwrap(), alias_metadata);
}
+ #[test]
+ fn test_nested_alias_resolves_child_field_once() -> Result<()> {
+ #[derive(Debug)]
+ struct CountingSchema {
+ field: FieldRef,
+ lookups: std::cell::Cell<usize>,
+ }
+
+ impl ExprSchema for CountingSchema {
+ fn nullable(&self, _col: &Column) -> Result<bool> {
+ Ok(self.field.is_nullable())
+ }
+
+ fn field_from_column(&self, _col: &Column) -> Result<&FieldRef> {
+ self.lookups.set(self.lookups.get() + 1);
+ Ok(&self.field)
+ }
+ }
+
+ let schema = CountingSchema {
+ field: Arc::new(Field::new("value", DataType::Int32,
false).with_metadata(
+ HashMap::from([
+ ("override".to_string(), "base".to_string()),
+ ("keep".to_string(), "base".to_string()),
+ ]),
+ )),
+ lookups: std::cell::Cell::new(0),
+ };
+ let mut expr = col("value");
+ for index in 0..12 {
+ let Expr::Alias(alias) = expr.alias(format!("alias_{index}")) else
{
Review Comment:
Optional simplification: Could we use
`expr.alias_with_metadata(format!("alias_{index}"), Some(...))` directly? It
performs the same alias construction and metadata attachment, avoiding the
destructuring and `unreachable!()` branch while preserving the existing
assertions.
##########
datafusion/expr/src/expr_schema.rs:
##########
@@ -1278,6 +1276,54 @@ mod tests {
assert_eq!(expr.metadata(&schema).unwrap(), alias_metadata);
}
+ #[test]
+ fn test_nested_alias_resolves_child_field_once() -> Result<()> {
+ #[derive(Debug)]
+ struct CountingSchema {
+ field: FieldRef,
+ lookups: std::cell::Cell<usize>,
+ }
+
+ impl ExprSchema for CountingSchema {
+ fn nullable(&self, _col: &Column) -> Result<bool> {
+ Ok(self.field.is_nullable())
+ }
+
+ fn field_from_column(&self, _col: &Column) -> Result<&FieldRef> {
+ self.lookups.set(self.lookups.get() + 1);
+ Ok(&self.field)
+ }
+ }
+
+ let schema = CountingSchema {
+ field: Arc::new(Field::new("value", DataType::Int32,
false).with_metadata(
+ HashMap::from([
+ ("override".to_string(), "base".to_string()),
+ ("keep".to_string(), "base".to_string()),
+ ]),
+ )),
+ lookups: std::cell::Cell::new(0),
+ };
+ let mut expr = col("value");
+ for index in 0..12 {
+ let Expr::Alias(alias) = expr.alias(format!("alias_{index}")) else
{
+ unreachable!();
+ };
+ expr = Expr::Alias(alias.with_metadata(Some(FieldMetadata::from(
+ HashMap::from([("override".to_string(), index.to_string())]),
+ ))));
+ }
+
+ let field = expr.to_field(&schema)?.1;
Review Comment:
Optional coverage: Consider constructing the outermost alias with
`alias_qualified_with_metadata(Some("outer"), format!("alias_{index}"),
Some(...))`, then destructuring `to_field` into `(relation, field)` and
asserting `assert_eq!(relation, Some(TableReference::bare("outer")))`. This
would additionally verify qualifier preservation while keeping the existing
field-name, lookup-count, and metadata assertions unchanged.
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