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[wip] update list & struct coercion to support incrementality #15259

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[wip] update list & struct coercion to support incrementality #15259

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8 changes: 7 additions & 1 deletion datafusion/datasource/src/schema_adapter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,8 @@ use arrow::array::{new_null_array, RecordBatch, RecordBatchOptions};
use arrow::compute::{can_cast_types, cast};
use arrow::datatypes::{Schema, SchemaRef};
use datafusion_common::plan_err;
use datafusion_expr::binary::struct_coercion;
use datafusion_expr::binary::list_coercion;
use std::fmt::Debug;
use std::sync::Arc;

Expand Down Expand Up @@ -269,7 +271,11 @@ impl SchemaAdapter for DefaultSchemaAdapter {
if let Some((table_idx, table_field)) =
self.projected_table_schema.fields().find(file_field.name())
{
match can_cast_types(file_field.data_type(), table_field.data_type()) {
match
can_cast_types(file_field.data_type(), table_field.data_type()) ||
struct_coercion(file_field.data_type(), table_field.data_type()).is_some() ||
list_coercion(file_field.data_type(), table_field.data_type()).is_some()
{
true => {
field_mappings[table_idx] = Some(projection.len());
projection.push(file_idx);
Expand Down
94 changes: 76 additions & 18 deletions datafusion/expr-common/src/type_coercion/binary.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -454,6 +454,27 @@ pub fn type_union_resolution(data_types: &[DataType]) -> Option<DataType> {
return Some(DataType::Utf8);
}

// Check if all data_types are Structs and coalescable
if data_types.iter().all(|t| matches!(t, DataType::Struct(_))) {
let mut max_cardinality_struct: Option<&DataType> = None;
for data_type in data_types.iter() {
if let Some(DataType::Struct(fields)) = max_cardinality_struct {
if let DataType::Struct(new_fields) = data_type {
if fields.len() == new_fields.len() {
max_cardinality_struct = Some(data_type);
} else if new_fields.len() > fields.len() {
max_cardinality_struct = Some(data_type);
}
}
} else {
max_cardinality_struct = Some(data_type);
}
}
if let Some(max_struct) = max_cardinality_struct {
return Some(max_struct.clone());
}
}

// Ignore Nulls, if any data_type category is not the same, return None
let data_types_category: Vec<TypeCategory> = data_types
.iter()
Expand Down Expand Up @@ -976,27 +997,48 @@ fn coerce_numeric_type_to_decimal256(numeric_type: &DataType) -> Option<DataType
}
}

fn struct_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
pub fn struct_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
use arrow::datatypes::DataType::*;
match (lhs_type, rhs_type) {
(Struct(lhs_fields), Struct(rhs_fields)) => {
if lhs_fields.len() != rhs_fields.len() {
return None;
}

let coerced_types = std::iter::zip(lhs_fields.iter(), rhs_fields.iter())
.map(|(lhs, rhs)| comparison_coercion(lhs.data_type(), rhs.data_type()))
.collect::<Option<Vec<DataType>>>()?;

// preserve the field name and nullability
let orig_fields = std::iter::zip(lhs_fields.iter(), rhs_fields.iter());
use std::collections::{HashMap, HashSet};
// Create maps from field name to field
let lhs_map: HashMap<String, FieldRef> = lhs_fields
.iter()
.map(|f| (f.name().clone(), Arc::clone(f)))
.collect();
let rhs_map: HashMap<String, FieldRef> = rhs_fields
.iter()
.map(|f| (f.name().clone(), Arc::clone(f)))
.collect();

let fields: Vec<FieldRef> = coerced_types
.into_iter()
.zip(orig_fields)
.map(|(datatype, (lhs, rhs))| coerce_fields(datatype, lhs, rhs))
// Compute the union of all field names
let keys: HashSet<String> = lhs_map
.keys()
.chain(rhs_map.keys())
.cloned()
.collect();
Some(Struct(fields.into()))

let mut coerced_fields: Vec<FieldRef> = Vec::new();
for key in keys {
let lhs_field = lhs_map.get(&key);
let rhs_field = rhs_map.get(&key);

// If a field is missing on one side, treat it as Null.
let lhs_dt = lhs_field.map(|f| f.data_type()).unwrap_or(&Null);
let rhs_dt = rhs_field.map(|f| f.data_type()).unwrap_or(&Null);

let coerced_dt = comparison_coercion(lhs_dt, rhs_dt)?;
// Determine nullability:
// - If the field is missing on one side, we consider it nullable.
// - Otherwise, true if either field is nullable.
let nullable = lhs_field.map(|f| f.is_nullable()).unwrap_or(true)
|| rhs_field.map(|f| f.is_nullable()).unwrap_or(true);
coerced_fields.push(Arc::new(Field::new(&key, coerced_dt, nullable)));
}
// Optionally, sort fields (here we sort alphabetically by name)
coerced_fields.sort_by(|a, b| a.name().cmp(b.name()));
Some(Struct(coerced_fields.into()))
}
_ => None,
}
Expand Down Expand Up @@ -1221,7 +1263,7 @@ fn coerce_list_children(lhs_field: &FieldRef, rhs_field: &FieldRef) -> Option<Fi
}

/// Coercion rules for list types.
fn list_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
pub fn list_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
use arrow::datatypes::DataType::*;
match (lhs_type, rhs_type) {
// Coerce to the left side FixedSizeList type if the list lengths are the same,
Expand Down Expand Up @@ -2240,7 +2282,6 @@ mod tests {
#[test]
fn test_list_coercion() {
let lhs_type = DataType::List(Arc::new(Field::new("lhs", DataType::Int8, false)));

let rhs_type = DataType::List(Arc::new(Field::new("rhs", DataType::Int64, true)));

let coerced_type = list_coercion(&lhs_type, &rhs_type).unwrap();
Expand All @@ -2250,6 +2291,23 @@ mod tests {
); // nullable because the RHS is nullable
}

#[test]
fn test_struct_coercion() {
let lhs_struct = DataType::Struct(vec![
Field::new("a", DataType::Int8, false),
Field::new("b", DataType::Int16, false),
].into());

let rhs_struct = DataType::Struct(vec![
Field::new("a", DataType::Int8, false),
Field::new("b", DataType::Int16, false),
Field::new("c", DataType::Int32, true),
].into());

let coerced_type = type_union_resolution(&[lhs_struct.clone(), rhs_struct.clone()]).unwrap();
assert_eq!(coerced_type, rhs_struct);
}

#[test]
fn test_type_coercion_logical_op() -> Result<()> {
test_coercion_binary_rule!(
Expand Down
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