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new f73922bdbf [Json] Support `FixedSizeList` in json decoder (#9715)
f73922bdbf is described below
commit f73922bdbfc727bc0af8cf89497c2a0eca6f5051
Author: Liam Bao <[email protected]>
AuthorDate: Tue Apr 21 10:41:51 2026 -0400
[Json] Support `FixedSizeList` in json decoder (#9715)
# Which issue does this PR close?
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enhancements and this helps us generate change logs for our releases.
You can link an issue to this PR using the GitHub syntax.
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- Closes #9714.
# Rationale for this change
<!--
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in the issue then this section is not needed.
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your changes and offer better suggestions for fixes.
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# What changes are included in this PR?
<!--
There is no need to duplicate the description in the issue here but it
is sometimes worth providing a summary of the individual changes in this
PR.
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Implement decoder for FixedSizeList
# Are these changes tested?
<!--
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1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code
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Yes
# Are there any user-facing changes?
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New decoding type supported
---
arrow-json/src/lib.rs | 38 +++++++++
arrow-json/src/reader/list_array.rs | 87 ++++++++++++++++++-
arrow-json/src/reader/mod.rs | 161 +++++++++++++++++++++++++++++++++++-
3 files changed, 284 insertions(+), 2 deletions(-)
diff --git a/arrow-json/src/lib.rs b/arrow-json/src/lib.rs
index 201c3cd807..9f2a9e3a81 100644
--- a/arrow-json/src/lib.rs
+++ b/arrow-json/src/lib.rs
@@ -390,4 +390,42 @@ mod tests {
assert_list_view_roundtrip::<i32>();
assert_list_view_roundtrip::<i64>();
}
+
+ #[test]
+ fn test_json_roundtrip_fixed_size_list() {
+ let inner = Arc::new(Field::new("item", DataType::Int32, true));
+ let schema = Arc::new(Schema::new(vec![
+ Field::new("flat", DataType::FixedSizeList(inner.clone(), 3),
true),
+ Field::new(
+ "nested",
+ DataType::FixedSizeList(
+ Arc::new(Field::new("item", DataType::FixedSizeList(inner,
2), true)),
+ 2,
+ ),
+ true,
+ ),
+ ]));
+
+ let input = r#"{"flat":[1,2,3],"nested":[[1,2],[3,4]]}
+{"flat":[4,null,5]}
+{"flat":[6,7,8],"nested":[[null,5],[6,null]]}
+"#
+ .as_bytes();
+
+ let batches: Vec<RecordBatch> = ReaderBuilder::new(schema.clone())
+ .with_batch_size(1024)
+ .build(Cursor::new(input))
+ .unwrap()
+ .collect::<Result<Vec<_>, _>>()
+ .unwrap();
+
+ let mut output = Vec::new();
+ let mut writer = WriterBuilder::new().build::<_, LineDelimited>(&mut
output);
+ for batch in &batches {
+ writer.write(batch).unwrap();
+ }
+ writer.finish().unwrap();
+
+ assert_eq!(input, &output);
+ }
}
diff --git a/arrow-json/src/reader/list_array.rs
b/arrow-json/src/reader/list_array.rs
index 9f9758b84f..ac574fab16 100644
--- a/arrow-json/src/reader/list_array.rs
+++ b/arrow-json/src/reader/list_array.rs
@@ -19,7 +19,9 @@ use std::marker::PhantomData;
use std::sync::Arc;
use arrow_array::builder::BooleanBufferBuilder;
-use arrow_array::{ArrayRef, GenericListArray, GenericListViewArray,
OffsetSizeTrait};
+use arrow_array::{
+ ArrayRef, FixedSizeListArray, GenericListArray, GenericListViewArray,
OffsetSizeTrait,
+};
use arrow_buffer::buffer::NullBuffer;
use arrow_buffer::{OffsetBuffer, ScalarBuffer};
use arrow_schema::{ArrowError, DataType, FieldRef};
@@ -134,3 +136,86 @@ impl<O: OffsetSizeTrait, const IS_VIEW: bool> ArrayDecoder
for ListLikeArrayDeco
}
}
}
+
+pub struct FixedSizeListArrayDecoder {
+ field: FieldRef,
+ size: i32,
+ decoder: Box<dyn ArrayDecoder>,
+ ignore_type_conflicts: bool,
+ is_nullable: bool,
+}
+
+impl FixedSizeListArrayDecoder {
+ pub fn new(
+ ctx: &DecoderContext,
+ data_type: &DataType,
+ is_nullable: bool,
+ ) -> Result<Self, ArrowError> {
+ let (field, size) = match data_type {
+ DataType::FixedSizeList(f, s) => (f, *s),
+ _ => unreachable!(),
+ };
+ let decoder = ctx.make_decoder(field.data_type(),
field.is_nullable())?;
+
+ Ok(Self {
+ field: field.clone(),
+ size,
+ decoder,
+ ignore_type_conflicts: ctx.ignore_type_conflicts(),
+ is_nullable,
+ })
+ }
+}
+
+impl ArrayDecoder for FixedSizeListArrayDecoder {
+ fn decode(&mut self, tape: &Tape<'_>, pos: &[u32]) -> Result<ArrayRef,
ArrowError> {
+ let expected = self.size as usize;
+ let mut child_pos = Vec::with_capacity(pos.len() * expected);
+
+ let mut nulls = self
+ .is_nullable
+ .then(|| BooleanBufferBuilder::new(pos.len()));
+
+ for p in pos {
+ let end_idx = match (tape.get(*p), nulls.as_mut()) {
+ (TapeElement::StartList(end_idx), None) => end_idx,
+ (TapeElement::StartList(end_idx), Some(nulls)) => {
+ nulls.append(true);
+ end_idx
+ }
+ (TapeElement::Null, Some(nulls)) => {
+ nulls.append(false);
+ child_pos.resize(child_pos.len() + expected, 0);
+ continue;
+ }
+ (_, Some(nulls)) if self.ignore_type_conflicts => {
+ nulls.append(false);
+ child_pos.resize(child_pos.len() + expected, 0);
+ continue;
+ }
+ _ => return Err(tape.error(*p, "[")),
+ };
+
+ let child_start = child_pos.len();
+ let mut cur_idx = *p + 1;
+ while cur_idx < end_idx {
+ child_pos.push(cur_idx);
+ cur_idx = tape.next(cur_idx, "fixed-size list value")?;
+ }
+
+ let actual = child_pos.len() - child_start;
+ if actual != expected {
+ return Err(ArrowError::JsonError(format!(
+ "Incorrect number of elements for FixedSizeList, \
+ expected {expected} but got {actual}"
+ )));
+ }
+ }
+
+ let values = self.decoder.decode(tape, &child_pos)?;
+ let nulls = nulls.as_mut().map(|x| NullBuffer::new(x.finish()));
+
+ let array = FixedSizeListArray::try_new(self.field.clone(), self.size,
values, nulls)?;
+ Ok(Arc::new(array))
+ }
+}
diff --git a/arrow-json/src/reader/mod.rs b/arrow-json/src/reader/mod.rs
index 32ac243283..04fe207c27 100644
--- a/arrow-json/src/reader/mod.rs
+++ b/arrow-json/src/reader/mod.rs
@@ -151,7 +151,9 @@ use crate::reader::binary_array::{
};
use crate::reader::boolean_array::BooleanArrayDecoder;
use crate::reader::decimal_array::DecimalArrayDecoder;
-use crate::reader::list_array::{ListArrayDecoder, ListViewArrayDecoder};
+use crate::reader::list_array::{
+ FixedSizeListArrayDecoder, ListArrayDecoder, ListViewArrayDecoder,
+};
use crate::reader::map_array::MapArrayDecoder;
use crate::reader::null_array::NullArrayDecoder;
use crate::reader::primitive_array::PrimitiveArrayDecoder;
@@ -835,6 +837,7 @@ fn make_decoder(
DataType::LargeList(_) =>
Ok(Box::new(ListArrayDecoder::<i64>::new(ctx, data_type, is_nullable)?)),
DataType::ListView(_) =>
Ok(Box::new(ListViewArrayDecoder::<i32>::new(ctx, data_type, is_nullable)?)),
DataType::LargeListView(_) =>
Ok(Box::new(ListViewArrayDecoder::<i64>::new(ctx, data_type, is_nullable)?)),
+ DataType::FixedSizeList(_, _) =>
Ok(Box::new(FixedSizeListArrayDecoder::new(ctx, data_type, is_nullable)?)),
DataType::Struct(_) => Ok(Box::new(StructArrayDecoder::new(ctx,
data_type, is_nullable)?)),
DataType::Binary => Ok(Box::new(BinaryArrayDecoder::<i32>::default())),
DataType::LargeBinary =>
Ok(Box::new(BinaryArrayDecoder::<i64>::default())),
@@ -2308,6 +2311,152 @@ mod tests {
assert_read_list_view::<i64>();
}
+ #[test]
+ fn test_fixed_size_list() {
+ let buf = r#"
+ {"a": [1, 2, 3]}
+ {"a": [4, 5, 6]}
+ {"a": [7, 8, 9]}
+ "#;
+
+ let field = Field::new_list_field(DataType::Int32, true);
+ let schema = Arc::new(Schema::new(vec![Field::new(
+ "a",
+ DataType::FixedSizeList(Arc::new(field), 3),
+ false,
+ )]));
+
+ let batches = do_read(buf, 1024, false, false, schema);
+ assert_eq!(batches.len(), 1);
+
+ let col = batches[0].column(0).as_fixed_size_list();
+ assert_eq!(col.len(), 3);
+ assert_eq!(col.value_length(), 3);
+
+ let values = col.values().as_primitive::<Int32Type>();
+ assert_eq!(values.values(), &[1, 2, 3, 4, 5, 6, 7, 8, 9]);
+ }
+
+ #[test]
+ fn test_fixed_size_list_nullable() {
+ let buf = r#"
+ {"a": [1, 2]}
+ {"a": null}
+ {"a": [3, null]}
+ "#;
+
+ let field = Field::new_list_field(DataType::Int32, true);
+ let schema = Arc::new(Schema::new(vec![Field::new(
+ "a",
+ DataType::FixedSizeList(Arc::new(field), 2),
+ true,
+ )]));
+
+ let batches = do_read(buf, 1024, false, false, schema);
+ assert_eq!(batches.len(), 1);
+
+ let col = batches[0].column(0).as_fixed_size_list();
+ assert_eq!(col.len(), 3);
+ assert!(col.is_valid(0));
+ assert!(col.is_null(1));
+ assert!(col.is_valid(2));
+
+ let values = col.values().as_primitive::<Int32Type>();
+ assert_eq!(values.value(0), 1);
+ assert_eq!(values.value(1), 2);
+ assert_eq!(values.value(4), 3);
+ assert!(values.is_null(5));
+ }
+
+ #[test]
+ fn test_fixed_size_list_wrong_size() {
+ let buf = r#"{"a": [1, 2, 3]}"#;
+
+ let field = Field::new_list_field(DataType::Int32, true);
+ let schema = Arc::new(Schema::new(vec![Field::new(
+ "a",
+ DataType::FixedSizeList(Arc::new(field), 2),
+ false,
+ )]));
+
+ let err = ReaderBuilder::new(schema)
+ .build(Cursor::new(buf.as_bytes()))
+ .unwrap()
+ .next()
+ .unwrap()
+ .unwrap_err();
+
+ assert!(err.to_string().contains("expected 2 but got 3"), "{}", err);
+ }
+
+ #[test]
+ fn test_fixed_size_list_nested() {
+ let buf = r#"
+ {"a": [[1, 2], [3, 4]]}
+ {"a": [[5, 6], [7, 8]]}
+ "#;
+
+ let inner_field = Field::new_list_field(DataType::Int32, true);
+ let inner_type = DataType::FixedSizeList(Arc::new(inner_field), 2);
+ let outer_field = Arc::new(Field::new_list_field(inner_type.clone(),
true));
+ let schema = Arc::new(Schema::new(vec![Field::new(
+ "a",
+ DataType::FixedSizeList(outer_field, 2),
+ false,
+ )]));
+
+ let batches = do_read(buf, 1024, false, false, schema);
+ assert_eq!(batches.len(), 1);
+
+ let col = batches[0].column(0).as_fixed_size_list();
+ assert_eq!(col.len(), 2);
+ assert_eq!(col.value_length(), 2);
+
+ let inner = col.values().as_fixed_size_list();
+ assert_eq!(inner.len(), 4);
+ assert_eq!(inner.value_length(), 2);
+
+ let values = inner.values().as_primitive::<Int32Type>();
+ assert_eq!(values.values(), &[1, 2, 3, 4, 5, 6, 7, 8]);
+ }
+
+ #[test]
+ fn test_fixed_size_list_ignore_type_conflicts() {
+ let field = Field::new("item", DataType::Int32, true);
+ let schema = Arc::new(Schema::new(vec![Field::new(
+ "a",
+ DataType::FixedSizeList(Arc::new(field), 2),
+ true,
+ )]));
+
+ let json = vec![
+ json!({"a": [1, 2]}),
+ json!({"a": "not a list"}),
+ json!({"a": 42}),
+ json!({"a": [6, 7]}),
+ ];
+
+ let mut decoder = ReaderBuilder::new(schema)
+ .with_ignore_type_conflicts(true)
+ .build_decoder()
+ .unwrap();
+ decoder.serialize(&json).unwrap();
+ let batch = decoder.flush().unwrap().unwrap();
+
+ let col = batch.column(0).as_fixed_size_list();
+ assert_eq!(col.len(), 4);
+ assert!(col.is_valid(0));
+ assert!(col.is_null(1)); // string -> null
+ assert!(col.is_null(2)); // number -> null
+ assert!(col.is_valid(3));
+
+ let values = col.values().as_primitive::<Int32Type>();
+ assert_eq!(values.value(0), 1);
+ assert_eq!(values.value(1), 2);
+ assert_eq!(values.value(6), 6);
+ assert_eq!(values.value(7), 7);
+ }
+
#[test]
fn test_skip_empty_lines() {
let schema = Schema::new(vec![Field::new("a", DataType::Int64, true)]);
@@ -3256,6 +3405,11 @@ mod tests {
DataType::List(Arc::new(Field::new("item", DataType::Int32,
true))),
false,
),
+ Field::new(
+ "fixed_size_list",
+ DataType::FixedSizeList(Arc::new(Field::new("item",
DataType::Int32, true)), 2),
+ false,
+ ),
Field::new(
"map",
DataType::Map(
@@ -3312,6 +3466,11 @@ mod tests {
DataType::List(Arc::new(Field::new("item", DataType::Int32,
true))),
true,
),
+ Field::new(
+ "fixed_size_list",
+ DataType::FixedSizeList(Arc::new(Field::new("item",
DataType::Int32, true)), 2),
+ true,
+ ),
Field::new(
"map",
DataType::Map(
