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fix(avro): error on complex (non-nullable) unions instead of silently dropping (#777) #808

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Merged
zeroshade merged 1 commit into from
May 13, 2026
+33 −3
Merged

fix(avro): error on complex (non-nullable) unions instead of silently dropping (#777) #808

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11 changes: 8 additions & 3 deletions arrow/avro/schema.go
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Original file line number Diff line number Diff line change
Expand Up @@ -139,13 +139,16 @@ func arrowSchemafromAvro(n *schemaNode) {
arrowSchemafromAvro(c)
n.arrowField = buildArrowField(n, arrow.MapOf(arrow.BinaryTypes.String, c.arrowField.Type), c.arrowField.Metadata)
case "union":
if n.schema.(*avro.UnionSchema).Nullable() {
if len(n.schema.(*avro.UnionSchema).Types()) > 1 {
n.schema = n.schema.(*avro.UnionSchema).Types()[1]
us := n.schema.(*avro.UnionSchema)
if us.Nullable() {
if len(us.Types()) > 1 {
n.schema = us.Types()[1]
n.union = true
n.nullable = true
arrowSchemafromAvro(n)
}
} else {
panic(fmt.Errorf("complex (non-nullable) avro union at '%v' is not supported", n.schemaPath()))
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@zeroshade zeroshade May 12, 2026

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Should we add support and use the arrow union type? We could also do this as a follow up instead.

}
// Avro "fixed" field type = Arrow FixedSize Primitive BinaryType
case "fixed":
Expand Down Expand Up @@ -245,6 +248,8 @@ func iterateFields(n *schemaNode) {
c.nullable = true
arrowSchemafromAvro(c)
}
} else {
panic(fmt.Errorf("complex (non-nullable) avro union in field '%v' is not supported", f.Name()))
}
default:
n.schemaCache.Add(f.Name(), f.Type())
Expand Down
25 changes: 25 additions & 0 deletions arrow/avro/schema_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,12 @@ package avro

import (
"fmt"
"strings"
"testing"

"github.com/apache/arrow-go/v18/arrow"
"github.com/apache/arrow-go/v18/arrow/avro/testdata"
avropkg "github.com/hamba/avro/v2"
)

func TestSchemaStringEqual(t *testing.T) {
Expand Down Expand Up @@ -174,3 +176,26 @@ func TestSchemaStringEqual(t *testing.T) {
})
}
}

func TestComplexUnionReportsError(t *testing.T) {
// Non-nullable union (e.g. [int, string]) is not supported and should
// produce a clear error rather than being silently dropped.
const avroSchemaJSON = `{
"type": "record",
"name": "WithComplexUnion",
"fields": [
{"name": "value", "type": ["int", "string"]}
]
}`
schema, err := avropkg.Parse(avroSchemaJSON)
if err != nil {
t.Fatalf("avro parse: %v", err)
}
got, err := ArrowSchemaFromAvro(schema)
if err == nil {
t.Fatalf("expected error for complex union, got schema=%v", got)
}
if !strings.Contains(err.Error(), "union") {
t.Fatalf("expected error to mention union, got: %v", err)
}
}