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Use try_new when casting between structs to propagate error #5226

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merged 3 commits into from
Dec 20, 2023
Merged

Use try_new when casting between structs to propagate error #5226

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e1688c8
Consider nullability when casting between structs
viirya Dec 19, 2023
a3bc7b0
Fix
viirya Dec 20, 2023
7cbed19
Remove
viirya Dec 20, 2023
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77 changes: 72 additions & 5 deletions arrow-cast/src/cast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -160,11 +160,18 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
(Decimal128(_, _) | Decimal256(_, _), Utf8 | LargeUtf8) => true,
// Utf8 to decimal
(Utf8 | LargeUtf8, Decimal128(_, _) | Decimal256(_, _)) => true,
(Struct(from_fields), Struct(to_fields)) => {
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Btw, "tab" was used in the merged code. It made incorrect ident in diff display. I fixed it to use space.

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Do we still need to update can_cast_types?

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You mean tab -> space fix or the added comment?

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I think it is better to fix the tab with space, otherwise the diff always shows a wrong indent.

The comment is good to have to explain why nullability is ignored there.

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Sorry, I saw modifications and thought you hadn't updated this 😅

from_fields.len() == to_fields.len() &&
from_fields.iter().zip(to_fields.iter()).all(|(f1, f2)| {
can_cast_types(f1.data_type(), f2.data_type())
})
(Struct(from_fields), Struct(to_fields)) => {
from_fields.len() == to_fields.len() &&
from_fields.iter().zip(to_fields.iter()).all(|(f1, f2)| {
// Only allows cast nullable or non-nullable fields to nullable fields.
// Although it is generally allowed to cast non-nullable fields to non-nullable fields,
// but if casting f1.data_type to f2.data_type may return null, e.g., overflow,
// it is not allowed when f2 is non-nullable. Because `can_cast_types` doesn't
// take `CastOptions` so we cannot check `safe` option here. We take safer
// approach to assume `safe` is true, so disallowing the case of casting non-nullable
// fields to non-nullable fields.
f2.is_nullable() && can_cast_types(f1.data_type(), f2.data_type())
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})
}
(Struct(_), _) => false,
(_, Struct(_)) => false,
Expand Down Expand Up @@ -9525,4 +9532,64 @@ mod tests {
result.unwrap_err().to_string()
);
}

#[test]
fn test_cast_struct_to_struct_disallow_nullability() {
let from_type = DataType::Struct(
vec![
Field::new("a", DataType::Boolean, true),
Field::new("b", DataType::Int32, true),
]
.into(),
);

// allow: nullable to nullable
let to_type = DataType::Struct(
vec![
Field::new("a", DataType::Utf8, true),
Field::new("b", DataType::Utf8, true),
]
.into(),
);
assert!(can_cast_types(&from_type, &to_type));

// disallow: nullable to non-nullable
let to_type = DataType::Struct(
vec![
Field::new("a", DataType::Utf8, true),
Field::new("b", DataType::Utf8, false),
]
.into(),
);
assert!(!can_cast_types(&from_type, &to_type));

let from_type = DataType::Struct(
vec![
Field::new("a", DataType::Boolean, false),
Field::new("b", DataType::Int32, false),
]
.into(),
);

// allow: non-nullable to nullable
let to_type = DataType::Struct(
vec![
Field::new("a", DataType::Utf8, true),
Field::new("b", DataType::Utf8, true),
]
.into(),
);
assert!(can_cast_types(&from_type, &to_type));

// disallow: non-nullable to non-nullable
// because casting may return null when overflow
let to_type = DataType::Struct(
vec![
Field::new("a", DataType::Utf8, true),
Field::new("b", DataType::Utf8, false),
]
.into(),
);
assert!(!can_cast_types(&from_type, &to_type));
}
}
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