TheNeuralBit commented on a change in pull request #14586:
URL: https://github.com/apache/beam/pull/14586#discussion_r636506720



##########
File path: 
sdks/java/extensions/arrow/src/main/java/org/apache/beam/sdk/extensions/arrow/ArrowConversion.java
##########
@@ -0,0 +1,524 @@
+/*
+ * 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.beam.sdk.extensions.arrow;
+
+import static 
org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.channels.Channels;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Optional;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+import org.apache.arrow.memory.RootAllocator;
+import org.apache.arrow.vector.FieldVector;
+import org.apache.arrow.vector.VectorLoader;
+import org.apache.arrow.vector.VectorSchemaRoot;
+import org.apache.arrow.vector.ipc.ReadChannel;
+import org.apache.arrow.vector.ipc.message.ArrowRecordBatch;
+import org.apache.arrow.vector.ipc.message.MessageSerializer;
+import org.apache.arrow.vector.types.TimeUnit;
+import org.apache.arrow.vector.types.pojo.ArrowType;
+import org.apache.arrow.vector.util.Text;
+import org.apache.beam.sdk.annotations.Experimental;
+import org.apache.beam.sdk.schemas.CachingFactory;
+import org.apache.beam.sdk.schemas.Factory;
+import org.apache.beam.sdk.schemas.FieldValueGetter;
+import org.apache.beam.sdk.schemas.Schema;
+import org.apache.beam.sdk.schemas.Schema.Field;
+import org.apache.beam.sdk.schemas.Schema.FieldType;
+import org.apache.beam.sdk.schemas.logicaltypes.FixedBytes;
+import org.apache.beam.sdk.values.Row;
+import org.joda.time.DateTime;
+import org.joda.time.DateTimeZone;
+
+/**
+ * Utilities to create {@link Iterable}s of Beam {@link Row} instances backed 
by Arrow record
+ * batches.
+ */
+@Experimental(Experimental.Kind.SCHEMAS)
+public class ArrowConversion {
+
+  /** Get Beam Field from Arrow Field. */
+  private static Field toBeamField(org.apache.arrow.vector.types.pojo.Field 
field) {
+    FieldType beamFieldType = toFieldType(field.getFieldType(), 
field.getChildren());
+    return Field.of(field.getName(), beamFieldType);
+  }
+
+  /** Converts Arrow FieldType to Beam FieldType. */
+  private static FieldType toFieldType(
+      org.apache.arrow.vector.types.pojo.FieldType arrowFieldType,
+      List<org.apache.arrow.vector.types.pojo.Field> childrenFields) {
+    FieldType fieldType =
+        arrowFieldType
+            .getType()
+            .accept(
+                new ArrowType.ArrowTypeVisitor<FieldType>() {
+                  @Override
+                  public FieldType visit(ArrowType.Null type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Struct type) {
+                    return 
FieldType.row(ArrowSchemaTranslator.toBeamSchema(childrenFields));
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.List type) {
+                    checkArgument(
+                        childrenFields.size() == 1,
+                        "Encountered "
+                            + childrenFields.size()
+                            + " child fields for list type, expected 1");
+                    return 
FieldType.array(toBeamField(childrenFields.get(0)).getType());
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.FixedSizeList type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Union type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Map type) {
+                    checkArgument(
+                        childrenFields.size() == 2,
+                        "Encountered "
+                            + childrenFields.size()
+                            + " child fields for map type, expected 2");
+                    return FieldType.map(
+                        toBeamField(childrenFields.get(0)).getType(),
+                        toBeamField(childrenFields.get(1)).getType());
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Int type) {
+                    if (!type.getIsSigned()) {
+                      throw new IllegalArgumentException("Unsigned integers 
are not supported.");
+                    }
+                    switch (type.getBitWidth()) {
+                      case 8:
+                        return FieldType.BYTE;
+                      case 16:
+                        return FieldType.INT16;
+                      case 32:
+                        return FieldType.INT32;
+                      case 64:
+                        return FieldType.INT64;
+                      default:
+                        throw new IllegalArgumentException(
+                            "Unsupported integer bit width: " + 
type.getBitWidth());
+                    }
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.FloatingPoint type) {
+                    switch (type.getPrecision()) {
+                      case SINGLE:
+                        return FieldType.FLOAT;
+                      case DOUBLE:
+                        return FieldType.DOUBLE;
+                      default:
+                        throw new IllegalArgumentException(
+                            "Unsupported floating-point precision: " + 
type.getPrecision().name());
+                    }
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Utf8 type) {
+                    return FieldType.STRING;
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Binary type) {
+                    return FieldType.BYTES;
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.FixedSizeBinary type) {
+                    return 
FieldType.logicalType(FixedBytes.of(type.getByteWidth()));
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Bool type) {
+                    return FieldType.BOOLEAN;
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Decimal type) {
+                    // FieldType.DECIMAL isn't perfect here since arrow 
decimal has a
+                    // scale/precision fixed by the schema, but 
FieldType.DECIMAL uses a BigDecimal,
+                    // whose precision/scale can change from row to row.
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Date type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Time type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Timestamp type) {
+                    if (type.getUnit() == TimeUnit.MILLISECOND
+                        || type.getUnit() == TimeUnit.MICROSECOND) {
+                      return FieldType.DATETIME;
+                    } else {
+                      throw new IllegalArgumentException(
+                          "Unsupported timestamp unit: " + 
type.getUnit().name());
+                    }
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Interval type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.Duration type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.LargeBinary type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.LargeUtf8 type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+
+                  @Override
+                  public FieldType visit(ArrowType.LargeList type) {
+                    throw new IllegalArgumentException(
+                        "Type \'" + type.toString() + "\' not supported.");
+                  }
+                });
+    return fieldType.withNullable(arrowFieldType.isNullable());
+  }
+
+  /**
+   * Returns an {@link Iterable<Row>} backed by the Arrow record batch stored 
in {@code
+   * vectorSchemaRoot}.
+   *
+   * <p>Note this is a lazy interface. The data in the underlying Arrow buffer 
is not read until a
+   * field of one of the returned {@link Row}s is accessed.
+   */
+  public static Iterable<Row> rowsFromRecordBatch(
+      Schema schema, VectorSchemaRoot vectorSchemaRoot) {
+    return new RecordBatchIterable(schema, vectorSchemaRoot);
+  }
+
+  public static Iterable<Row> rowsFromRecordBatch(VectorSchemaRoot 
vectorSchemaRoot) {
+    return rowsFromRecordBatch(
+        ArrowSchemaTranslator.toBeamSchema(vectorSchemaRoot.getSchema()), 
vectorSchemaRoot);
+  }
+
+  public static VectorSchemaRoot rowFromSerializedRecordBatch(InputStream 
input)

Review comment:
       nit:
   ```suggestion
     public static VectorSchemaRoot rowsFromSerializedRecordBatch(InputStream 
input)
   ```
   Could you modify this to return an `Iterable<Row>` by calling 
`rowsFromRecordBatch`?
   
   We also need to manage the lifecycle of the `ReadChannel` and 
`RootAllocator` created in this method, by close()-ing them when done, 
otherwise we could leak memory. Probably what we should do is make sure the 
iterator has a reference to these objects, then it can close() them in it's own 
close method. You could do this either by passing those objects to the 
Iterable/Iterator, or making the Iterable responsible for creating them.
   
   Then we'll have to call `close()` in `BigQueryStorageArrowReader.close`, and 
`BigQueryStorageArrowReader.resetBuffer`.

##########
File path: 
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/SchemaAndRecord.java
##########
@@ -18,23 +18,32 @@
 package org.apache.beam.sdk.io.gcp.bigquery;
 
 import com.google.api.services.bigquery.model.TableSchema;
+import javax.annotation.Nullable;
 import org.apache.avro.generic.GenericRecord;
+import org.apache.beam.sdk.values.Row;
 
 /**
  * A wrapper for a {@link GenericRecord} and the {@link TableSchema} 
representing the schema of the
  * table (or query) it was generated from.
  */
 public class SchemaAndRecord {
-  private final GenericRecord record;
+  private final Object record;
   private final TableSchema tableSchema;
 
-  public SchemaAndRecord(GenericRecord record, TableSchema tableSchema) {
+  public SchemaAndRecord(Object record, TableSchema tableSchema) {
     this.record = record;
     this.tableSchema = tableSchema;
   }
 
   public GenericRecord getRecord() {
-    return record;
+    if (!(record instanceof GenericRecord)) {
+      throw new IllegalStateException("Object is not GenericRecord");
+    }
+    return (GenericRecord) record;
+  }

Review comment:
       Do we still need the ability to for `record` to be a `GenericRecord`? I 
thought the plan was for `record` to always be a `Row`?




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