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https://issues.apache.org/jira/browse/BEAM-5918?focusedWorklogId=160705&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-160705
]
ASF GitHub Bot logged work on BEAM-5918:
----------------------------------------
Author: ASF GitHub Bot
Created on: 30/Oct/18 16:20
Start Date: 30/Oct/18 16:20
Worklog Time Spent: 10m
Work Description: kennknowles commented on a change in pull request
#6888: [BEAM-5918] [WIP] Add Cast transform for Rows
URL: https://github.com/apache/beam/pull/6888#discussion_r229376846
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/transforms/Cast.java
##########
@@ -0,0 +1,582 @@
+/*
+ * 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.schemas.transforms;
+
+import static org.apache.beam.sdk.schemas.Schema.TypeName.ARRAY;
+import static org.apache.beam.sdk.schemas.Schema.TypeName.INT16;
+import static org.apache.beam.sdk.schemas.Schema.TypeName.INT32;
+import static org.apache.beam.sdk.schemas.Schema.TypeName.INT64;
+import static org.apache.beam.sdk.schemas.Schema.TypeName.MAP;
+import static org.apache.beam.sdk.schemas.Schema.TypeName.ROW;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Maps;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import org.apache.beam.sdk.annotations.Experimental;
+import org.apache.beam.sdk.schemas.FieldAccessDescriptor;
+import org.apache.beam.sdk.schemas.Schema;
+import org.apache.beam.sdk.schemas.Schema.TypeName;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.apache.beam.sdk.transforms.PTransform;
+import org.apache.beam.sdk.transforms.ParDo;
+import org.apache.beam.sdk.values.KV;
+import org.apache.beam.sdk.values.PCollection;
+import org.apache.beam.sdk.values.Row;
+
+/** Set of utilities for casting rows between schemas. */
+@Experimental(Experimental.Kind.SCHEMAS)
+@AutoValue
+public abstract class Cast<T> extends PTransform<PCollection<T>,
PCollection<Row>> {
+
+ public abstract Schema outputSchema();
+
+ public abstract Nullability nullability();
+
+ public abstract Type type();
+
+ public abstract Shape shape();
+
+ /** Builder for {@link Cast}. */
+ @AutoValue.Builder
+ public abstract static class Builder<T> {
+
+ public abstract Builder<T> outputSchema(Schema schema);
+
+ public abstract Builder<T> nullability(Nullability nullability);
+
+ public abstract Builder<T> type(Type type);
+
+ public abstract Builder<T> shape(Shape shape);
+
+ public abstract Cast<T> build();
+ }
+
+ public static <T> Builder<T> builder() {
+ return new AutoValue_Cast.Builder<T>();
+ }
+
+ public static <T> Cast<T> to(Schema outputSchema) {
+ return Cast.<T>builder()
+ .outputSchema(outputSchema)
+ .nullability(Nullability.IGNORE)
+ .type(Type.WIDEN)
+ .shape(Shape.PROJECTION)
+ .build();
+ }
+
+ public List<CompatibilityError> compatibility(Schema inputSchema) {
+ return Inference.compatibility(inputSchema, outputSchema(), nullability(),
type(), shape());
+ }
+
+ public void verifyCompatibility(Schema inputSchema) {
+ List<CompatibilityError> errors = compatibility(inputSchema);
+
+ if (!errors.isEmpty()) {
+ String reason =
+ errors
+ .stream()
+ .map(x -> Joiner.on('.').join(x.path()) + ": " + x.message())
+ .collect(Collectors.joining("\n\t"));
+
+ throw new IllegalArgumentException("Cast isn't compatible:\n\t" +
reason);
+ }
+ }
+
+ @Override
+ public PCollection<Row> expand(PCollection<T> input) {
+ Schema inputSchema = input.getSchema();
+
+ verifyCompatibility(inputSchema);
+
+ return input
+ .apply(
+ ParDo.of(
+ new DoFn<T, Row>() {
+ // TODO: This should be the same as resolved so that Beam
knows which fields
+ // are being accessed. Currently Beam only supports wildcard
descriptors.
+ // Once BEAM-4457 is fixed, fix this.
+ @FieldAccess("filterFields")
+ final FieldAccessDescriptor fieldAccessDescriptor =
+ FieldAccessDescriptor.withAllFields();
+
+ @ProcessElement
+ public void process(@FieldAccess("filterFields") Row row,
OutputReceiver<Row> r) {
+ r.output(castRow(row, inputSchema, outputSchema()));
+ }
+ }))
+ .setRowSchema(outputSchema());
+ }
+
+ @VisibleForTesting
+ static Row castRow(Row input, Schema inputSchema, Schema outputSchema) {
+ Row.Builder output = Row.withSchema(outputSchema);
+ for (int i = 0; i < outputSchema.getFieldCount(); i++) {
+ Schema.Field outputField = outputSchema.getField(i);
+
+ int fromFieldIdx = inputSchema.indexOf(outputField.getName());
+ Schema.Field inputField = inputSchema.getField(fromFieldIdx);
+
+ Object inputValue = input.getValue(fromFieldIdx);
+
+ if (inputValue == null) {
+ output.addValue(null);
+ } else {
+ Object value = castObject(inputValue, inputField.getType(),
outputField.getType());
+ output.addValue(value);
+ }
+ }
+
+ return output.build();
+ }
+
+ @VisibleForTesting
+ @SuppressWarnings("unchecked")
+ static Object castObject(
+ Object inputValue, Schema.FieldType inputFieldType, Schema.FieldType
outputFieldType) {
+
+ if (inputFieldType.getTypeName() == ROW) {
+ return castRow(
+ (Row) inputValue, inputFieldType.getRowSchema(),
outputFieldType.getRowSchema());
+ } else if (inputFieldType.getTypeName() == ARRAY) {
+ List<Object> inputValues = (List<Object>) inputValue;
+ List<Object> outputValues = new ArrayList<>(inputValues.size());
+
+ for (Object elem : inputValues) {
+ outputValues.add(
+ castObject(
+ elem,
+ inputFieldType.getCollectionElementType(),
+ outputFieldType.getCollectionElementType()));
+ }
+
+ return outputValues;
+ } else if (inputFieldType.getTypeName() == MAP) {
+ Map<Object, Object> inputMap = (Map<Object, Object>) inputValue;
+ Map<Object, Object> outputMap =
Maps.newHashMapWithExpectedSize(inputMap.size());
+
+ for (Map.Entry<Object, Object> entry : inputMap.entrySet()) {
+ Object outputKey =
+ castObject(
+ entry.getKey(), inputFieldType.getMapKeyType(),
outputFieldType.getMapKeyType());
+ Object outputValue =
+ castObject(
+ entry.getValue(),
+ inputFieldType.getMapValueType(),
+ outputFieldType.getMapValueType());
+
+ outputMap.put(outputKey, outputValue);
+ }
+
+ return outputMap;
+ } else {
+ if (inputFieldType.getTypeName().equals(outputFieldType.getTypeName())) {
+ return inputValue;
+ } else {
+ KV<TypeName, TypeName> key =
+ KV.of(inputFieldType.getTypeName(), outputFieldType.getTypeName());
+ return Inference.ALL_MAP.get(key).apply(inputValue);
+ }
+ }
+ }
+
+ /** Configures casting for nullable fields. */
+ public enum Nullability {
+ /** Can cast only if nullability is the same. */
+ SAME,
+ /** Can cast non-nullable fields to nullable. */
+ WEAKEN,
+ /** Can cast nullable fields to non-nullable and forth. */
+ IGNORE
Review comment:
The term `IGNORE` might be misleading. This would be a failed cast if the
input is null. FWIW in this type system you can consider `NULLABLE t` to be a
supertype of `t` so it is perfectly analogous to the `Type` enum.
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Issue Time Tracking
-------------------
Worklog Id: (was: 160705)
Time Spent: 50m (was: 40m)
> Add Cast transform for Rows
> ---------------------------
>
> Key: BEAM-5918
> URL: https://issues.apache.org/jira/browse/BEAM-5918
> Project: Beam
> Issue Type: Improvement
> Components: sdk-java-core
> Reporter: Gleb Kanterov
> Assignee: Kenneth Knowles
> Priority: Major
> Time Spent: 50m
> Remaining Estimate: 0h
>
> There is a need for a generic transform that given two Row schemas will
> convert rows between them. There must be a possibility to opt-out from
> certain kind of conversions, for instance, converting ints to shorts can
> cause overflow. Another example, a schema could have a nullable field, but
> never have NULL value in practice, because it was filtered out.
> What is needed:
> - widening values (e.g., int -> long)
> - narrowwing (e.g., int -> short)
> - runtime check for overflow while narrowing
> - ignoring nullability (nullable=true -> nullable=false)
> - weakening nullability (nullable=false -> nullable=true)
> - projection (Schema(a: Int32, b: Int32) -> Schema(a: Int32))
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