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fix: make Parquet file schema type coercion work on nested schemas #25193

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fix: make Parquet file schema type coercion work on nested schemas #25193

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292 changes: 291 additions & 1 deletion datafusion/datasource-parquet/src/schema_coercion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,7 @@ pub fn apply_file_schema_type_coercions(
) -> Option<Schema> {
let mut needs_view_transform = false;
let mut needs_string_transform = false;
let mut needs_nested_transform = false;

// Create a mapping of table field names to their data types for fast lookup
// and simultaneously check if we need any transformations
Expand All @@ -72,13 +73,26 @@ pub fn apply_file_schema_type_coercions(
) {
needs_string_transform = true;
}
// Nested fields can need transformations even when their parent does not.
if matches!(
dt,
DataType::Struct(_)
| DataType::List(_)
| DataType::LargeList(_)
| DataType::ListView(_)
| DataType::LargeListView(_)
| DataType::FixedSizeList(_, _)
| DataType::Map(_, _)
) {
needs_nested_transform = true;
}

(f.name(), dt)
})
.collect();

// Early return if no transformation needed
if !needs_view_transform && !needs_string_transform {
if !needs_view_transform && !needs_string_transform && !needs_nested_transform {
return None;
}

Expand Down Expand Up @@ -120,6 +134,42 @@ pub fn apply_file_schema_type_coercions(
(&DataType::BinaryView, DataType::Binary | DataType::LargeBinary) => {
return field_with_new_type(field, DataType::BinaryView);
}
// Apply the same coercions to matching fields inside structs.
(DataType::Struct(table_fields), DataType::Struct(file_fields)) => {
if let Some(schema) = apply_file_schema_type_coercions(
&Schema::new(table_fields.clone()),
&Schema::new(file_fields.clone()),
) {
return field_with_new_type(field, DataType::Struct(schema.fields));
}
}
// Container children match by position, regardless of their names.
(DataType::List(table_child), DataType::List(file_child))
| (DataType::LargeList(table_child), DataType::LargeList(file_child))
| (DataType::ListView(table_child), DataType::ListView(file_child))
| (DataType::LargeListView(table_child), DataType::LargeListView(file_child))
| (DataType::FixedSizeList(table_child, _), DataType::FixedSizeList(file_child, _))
| (DataType::Map(table_child, _), DataType::Map(file_child, _)) => {
if let Some(schema) = apply_file_schema_type_coercions(
&Schema::new(vec![field_with_new_type(
file_child,
table_child.data_type().clone(),
)]),
&Schema::new(vec![Arc::clone(file_child)]),
) {
let child = Arc::clone(&schema.fields()[0]);
let new_type = match field_type {
DataType::List(_) => DataType::List(child),
DataType::LargeList(_) => DataType::LargeList(child),
DataType::ListView(_) => DataType::ListView(child),
DataType::LargeListView(_) => DataType::LargeListView(child),
DataType::FixedSizeList(_, size) => DataType::FixedSizeList(child, *size),
DataType::Map(_, sorted) => DataType::Map(child, *sorted),
_ => return Arc::clone(field),
};
return field_with_new_type(field, new_type);
}
}
_ => {}
}
}
Expand All @@ -129,6 +179,10 @@ pub fn apply_file_schema_type_coercions(
})
.collect();

if transformed_fields.iter().eq(file_schema.fields().iter()) {
return None;
}

Some(Schema::new_with_metadata(
transformed_fields,
file_schema.metadata.clone(),
Expand Down Expand Up @@ -470,6 +524,242 @@ mod tests {

use parquet::schema::parser::parse_message_type;

#[test]
fn nested_coercion_preserves_file_schema() {
let field_metadata = HashMap::from([("source".into(), "file".into())]);
let identifiers = Field::new_struct(
"identifiers",
vec![Field::new("cid", DataType::Utf8, true)],
true,
)
.with_metadata(field_metadata.clone());
let struct_field = Field::new_struct(
"_struct",
vec![
Field::new("file_only", DataType::Binary, true),
identifiers.clone(),
],
true,
)
.with_metadata(field_metadata.clone());
let file_schema = Schema::new_with_metadata(
vec![Field::new("id", DataType::Int64, false), struct_field.clone()],
field_metadata.clone(),
);
let table_schema = Schema::new(vec![
Field::new_struct(
"_struct",
vec![
Field::new_struct(
"identifiers",
vec![Field::new("cid", DataType::Utf8View, false)],
false,
),
Field::new("schemaEvolutionOnly", DataType::Utf8View, true),
],
false,
),
Field::new("missing", DataType::Utf8View, true),
Field::new("id", DataType::Int64, true),
]);
let expected = Schema::new_with_metadata(
vec![
Field::new("id", DataType::Int64, false),
struct_field.with_data_type(DataType::Struct(
vec![
Field::new("file_only", DataType::Binary, true),
identifiers.with_data_type(DataType::Struct(
vec![Field::new("cid", DataType::Utf8View, true)].into(),
)),
]
.into(),
)),
],
field_metadata,
);

let result = apply_file_schema_type_coercions(&table_schema, &file_schema);
assert_eq!(result, Some(expected.clone()));
assert_eq!(
apply_file_schema_type_coercions(&table_schema, &expected),
None
);
}

#[test]
fn nested_coercion_preserves_list_containers() {
let wrap: [fn(FieldRef) -> DataType; 6] = [
DataType::List,
DataType::LargeList,
DataType::ListView,
DataType::LargeListView,
|field| DataType::FixedSizeList(field, 3),
|field| DataType::Map(field, false),
];
for wrap in wrap {
let file_element = Arc::new(Field::new_struct(
"entries",
vec![
Field::new("key", DataType::Utf8, false),
Field::new("value", DataType::Binary, true),
],
false,
));
let table_element = Arc::new(Field::new_struct(
"entries",
vec![
Field::new("value", DataType::Utf8View, true),
Field::new("key", DataType::Utf8View, false),
],
false,
));
let expected_element = Arc::new(Field::new_struct(
"entries",
vec![
Field::new("key", DataType::Utf8View, false),
Field::new("value", DataType::Utf8View, true),
],
false,
));
let file_schema =
Schema::new(vec![Field::new("data", wrap(file_element), true)]);
let table_schema =
Schema::new(vec![Field::new("data", wrap(table_element), true)]);
let expected =
Schema::new(vec![Field::new("data", wrap(expected_element), true)]);
assert_eq!(
apply_file_schema_type_coercions(&table_schema, &file_schema),
Some(expected)
);
}
}

#[test]
fn nested_coercion_preserves_leaf_conversion_rules() {
for (table_type, file_types) in [
(
DataType::Utf8,
vec![
DataType::Binary,
DataType::LargeBinary,
DataType::BinaryView,
],
),
(
DataType::LargeUtf8,
vec![
DataType::Binary,
DataType::LargeBinary,
DataType::BinaryView,
],
),
(
DataType::Utf8View,
vec![
DataType::Binary,
DataType::LargeBinary,
DataType::BinaryView,
DataType::Utf8,
DataType::LargeUtf8,
],
),
(
DataType::BinaryView,
vec![DataType::Binary, DataType::LargeBinary],
),
] {
for file_type in file_types {
let file_schema = Schema::new(vec![Field::new("value", file_type, true)]);
let table_schema =
Schema::new(vec![Field::new("value", table_type.clone(), true)]);
assert_eq!(
apply_file_schema_type_coercions(&table_schema, &file_schema),
Some(table_schema)
);
}
}
let file_schema = Schema::new(vec![Field::new("value", DataType::Int32, true)]);
let table_schema = Schema::new(vec![Field::new("value", DataType::Int64, true)]);
assert_eq!(
apply_file_schema_type_coercions(&table_schema, &file_schema),
None
);
}

#[test]
fn nested_coercion_reader_produces_string_views() {
use arrow::array::{Array, ArrayRef, StringArray, StringViewArray, StructArray};
use arrow::record_batch::RecordBatch;
use bytes::Bytes;
use parquet::arrow::ArrowWriter;
use parquet::arrow::arrow_reader::{
ArrowReaderOptions, ParquetRecordBatchReaderBuilder,
};

let identifiers = StructArray::from(vec![(
Arc::new(Field::new("cid", DataType::Utf8, true)),
Arc::new(StringArray::from(vec![Some("customer-03"), None])) as ArrayRef,
)]);
let struct_field = StructArray::from(vec![(
Arc::new(Field::new(
"identifiers",
identifiers.data_type().clone(),
true,
)),
Arc::new(identifiers) as ArrayRef,
)]);
let batch = RecordBatch::try_from_iter([("_struct", Arc::new(struct_field) as ArrayRef)])
.unwrap();
let table_schema = Schema::new(vec![Field::new_struct(
"_struct",
vec![
Field::new_struct(
"identifiers",
vec![Field::new("cid", DataType::Utf8View, true)],
true,
),
Field::new("schemaEvolutionOnly", DataType::Utf8View, true),
],
true,
)]);
let reader_schema = Arc::new(
apply_file_schema_type_coercions(&table_schema, &batch.schema())
.unwrap(),
);
let mut bytes = Vec::new();
let mut writer = ArrowWriter::try_new(&mut bytes, batch.schema(), None).unwrap();
writer.write(&batch).unwrap();
writer.close().unwrap();
let mut reader = ParquetRecordBatchReaderBuilder::try_new_with_options(
Bytes::from(bytes),
ArrowReaderOptions::new().with_schema(reader_schema),
)
.unwrap()
.build()
.unwrap();
let decoded = reader.next().unwrap().unwrap();
let struct_field = decoded
.column(0)
.as_any()
.downcast_ref::<StructArray>()
.unwrap();
let identifiers = struct_field
.column(0)
.as_any()
.downcast_ref::<StructArray>()
.unwrap();
let cust_id = identifiers
.column(0)
.as_any()
.downcast_ref::<StringViewArray>()
.unwrap();
assert_eq!(cust_id.value(0), "customer-03");
assert!(cust_id.is_null(1));
assert_eq!(struct_field.num_columns(), 1);
assert!(reader.next().is_none());
}


#[test]
fn coerce_int96_to_resolution_with_mixed_timestamps() {
// Unclear if Spark (or other writer) could generate a file with mixed timestamps like this,
Expand Down
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