Add a union type

Author: martin-traverse

adapter/avro/src/main/java/org/apache/arrow/adapter/avro/ArrowToAvroUtils.java

@@ -30,6 +30,7 @@
 import org.apache.arrow.adapter.avro.producers.AvroNullableProducer;
 import org.apache.arrow.adapter.avro.producers.AvroStringProducer;
 import org.apache.arrow.adapter.avro.producers.AvroStructProducer;
+import org.apache.arrow.adapter.avro.producers.AvroUnionsProducer;
 import org.apache.arrow.adapter.avro.producers.BaseAvroProducer;
 import org.apache.arrow.adapter.avro.producers.CompositeAvroProducer;
 import org.apache.arrow.adapter.avro.producers.Producer;
@@ -59,6 +60,7 @@
 import org.apache.arrow.vector.complex.ListVector;
 import org.apache.arrow.vector.complex.MapVector;
 import org.apache.arrow.vector.complex.StructVector;
+import org.apache.arrow.vector.complex.UnionVector;
 import org.apache.arrow.vector.types.Types;
 
 import java.util.ArrayList;
@@ -93,13 +95,15 @@ private static BaseAvroProducer<?> createProducer(FieldVector vector, boolean nu
 
     Preconditions.checkNotNull(vector, "Arrow vector object can't be null");
 
-    if (nullable) {
+    final Types.MinorType minorType = vector.getMinorType();
+
+    // Avro understands nullable types as a union of type | null
+    // Most nullable fields in a VSR will not be unions, so provide a special wrapper
+    if (nullable && minorType != Types.MinorType.UNION) {
       final BaseAvroProducer<?> innerProducer = createProducer(vector, false);
       return new AvroNullableProducer<>(innerProducer);
     }
 
-    final Types.MinorType minorType = vector.getMinorType();
-
     switch (minorType) {
 
       // Primitive types with direct mapping to Avro
@@ -169,6 +173,17 @@ private static BaseAvroProducer<?> createProducer(FieldVector vector, boolean nu
         Producer<?> entryProducer = new AvroStructProducer(entryVector, new Producer<?>[] {keyProducer, valueProducer});
         return new AvroMapProducer(mapVector, entryProducer);
 
+      case UNION:
+
+        UnionVector unionVector = (UnionVector) vector;
+        List<FieldVector> unionChildVectors = unionVector.getChildrenFromFields();
+        Producer<?>[] unionChildProducers = new Producer<?>[unionChildVectors.size()];
+        for (int i = 0; i < unionChildVectors.size(); i++) {
+          FieldVector unionChildVector = unionChildVectors.get(i);
+          unionChildProducers[i] = createProducer(unionChildVector, /* nullable = */ false);  // Do not nest union types
+        }
+        return new AvroUnionsProducer(unionVector, unionChildProducers);
+
       // Not all Arrow types are supported for encoding (yet)!
 
       default:

adapter/avro/src/main/java/org/apache/arrow/adapter/avro/producers/AvroUnionsProducer.java

@@ -0,0 +1,112 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.arrow.adapter.avro.producers;
+
+import org.apache.arrow.vector.FieldVector;
+import org.apache.arrow.vector.complex.UnionVector;
+import org.apache.arrow.vector.types.Types;
+import org.apache.arrow.vector.types.UnionMode;
+import org.apache.avro.io.Encoder;
+
+import java.io.IOException;
+import java.util.List;
+
+/**
+ * Producer which produces unions type values to avro encoder. Write the data to
+ * {@link org.apache.arrow.vector.complex.UnionVector}.
+ */
+public class AvroUnionsProducer extends BaseAvroProducer<UnionVector> {
+
+  private final Producer<?>[] delegates;
+  private final UnionMode unionMode;
+  private final int nullTypeIndex;
+
+  /** Instantiate an AvroUnionsProducer. */
+  public AvroUnionsProducer(UnionVector vector, Producer<?>[] delegates) {
+    super(vector);
+    this.delegates = delegates;
+    this.unionMode = vector.getMinorType() == Types.MinorType.DENSEUNION ? UnionMode.Dense : UnionMode.Sparse;
+    this.nullTypeIndex = findNullTypeIndex();
+  }
+
+  private int findNullTypeIndex() {
+    List<FieldVector> childVectors = vector.getChildrenFromFields();
+    for (int i = 0; i < childVectors.size(); i++) {
+      if (childVectors.get(i).getMinorType() == Types.MinorType.NULL) {
+        return i;
+      }
+    }
+    // For nullable unions with no explicit null type, a null type is appended to the schema
+    return childVectors.size();
+  }
+
+  @Override
+  public void produce(Encoder encoder) throws IOException {
+
+    if (vector.isNull(currentIndex)) {
+      encoder.writeInt(nullTypeIndex);
+      encoder.writeNull();
+    }
+    else {
+
+      int typeIndex = vector.getTypeValue(currentIndex);
+      int typeVectorIndex;
+
+      if (unionMode == UnionMode.Dense) {
+        typeVectorIndex = vector.getOffsetBuffer().getInt(currentIndex * (long) Integer.BYTES);
+      }
+      else {
+        typeVectorIndex = currentIndex;
+      }
+
+      FieldVector typeVector = vector.getChildrenFromFields().get(typeIndex);
+
+      if (typeVector.isNull(typeVectorIndex)) {
+        encoder.writeInt(nullTypeIndex);
+        encoder.writeNull();
+      }
+      else {
+        Producer<?> delegate = delegates[typeIndex];
+        encoder.writeInt(typeIndex);
+        delegate.setPosition(typeVectorIndex);
+        delegate.produce(encoder);
+      }
+    }
+
+    currentIndex++;
+  }
+
+  @Override
+  @SuppressWarnings("unchecked")
+  public boolean resetValueVector(UnionVector vector) {
+    boolean result = true;
+    for (int i = 0; i < delegates.length; i++) {
+      Producer<FieldVector> delegate = (Producer<FieldVector>) delegates[i];
+      result &= delegate.resetValueVector(vector.getChildrenFromFields().get(i));
+    }
+    return result & super.resetValueVector(vector);
+  }
+
+  @Override
+  public void close() throws Exception {
+    for (Producer<?> delegate : delegates) {
+      delegate.close();
+    }
+    super.close();
+  }
+}