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https://issues.apache.org/jira/browse/BEAM-5918?focusedWorklogId=162654&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-162654
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ASF GitHub Bot logged work on BEAM-5918:
----------------------------------------
Author: ASF GitHub Bot
Created on: 05/Nov/18 18:23
Start Date: 05/Nov/18 18:23
Worklog Time Spent: 10m
Work Description: kennknowles commented on a change in pull request
#6888: [BEAM-5918] Add Cast transform for Rows
URL: https://github.com/apache/beam/pull/6888#discussion_r230857029
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/transforms/Cast.java
##########
@@ -0,0 +1,440 @@
+/*
+ * 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 com.google.auto.value.AutoValue;
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Maps;
+import java.io.Serializable;
+import java.math.BigDecimal;
+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 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.Field;
+import org.apache.beam.sdk.schemas.Schema.FieldType;
+import org.apache.beam.sdk.schemas.Schema.TypeName;
+import org.apache.beam.sdk.schemas.utils.SchemaZipFold;
+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.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 Validator validator();
+
+ public static <T> Cast<T> of(Schema outputSchema, Validator validator) {
+ return new AutoValue_Cast<>(outputSchema, validator);
+ }
+
+ public static <T> Cast<T> widening(Schema outputSchema) {
+ return new AutoValue_Cast<>(outputSchema, Widening.of());
+ }
+
+ public static <T> Cast<T> narrowing(Schema outputSchema) {
+ return new AutoValue_Cast<>(outputSchema, Narrowing.of());
+ }
+
+ /** Describes compatibility errors during casting. */
+ @AutoValue
+ public abstract static class CompatibilityError implements Serializable {
+
+ public abstract List<String> path();
+
+ public abstract String message();
+
+ public static CompatibilityError create(List<String> path, String message)
{
+ return new AutoValue_Cast_CompatibilityError(path, message);
+ }
+ }
+
+ /** Interface for statically validating casts. */
+ public interface Validator extends Serializable {
+ List<CompatibilityError> apply(Schema input, Schema output);
+ }
+
+ /**
+ * Widening changes to type that can represent any possible value of the
original type.
+ *
+ * <p>Standard widening conversions:
+ *
+ * <ul>
+ * <li>BYTE to INT16, INT32, INT64, FLOAT, DOUBLE, DECIMAL
+ * <li>INT16 to INT32, INT64, FLOAT, DOUBLE, DECIMAL
+ * <li>INT32 to INT64, FLOAT, DOUBLE, DECIMAL
+ * <li>INT64 to FLOAT, DOUBLE, DECIMAL
+ * <li>FLOAT to DOUBLE, DECIMAL
+ * <li>DOUBLE to DECIMAL
+ * </ul>
+ *
+ * <p>Row widening:
+ *
+ * <ul>
+ * <li>wider schema to schema with a subset of fields
+ * <li>non-nullable fields to nullable fields
+ * </ul>
+ *
+ * <p>Widening doesn't lose information about the overall magnitude in
following cases:
+ *
+ * <ul>
+ * <li>integral type to another integral type
+ * <li>BYTE or INT16 to FLOAT, DOUBLE or DECIMAL
+ * <li>INT32 to DOUBLE
+ * </ul>
+ *
+ * <p>Other conversions to may cause loss of precision.
+ */
+ public static class Widening implements Validator {
+ private final Fold fold = new Fold();
+
+ public static Widening of() {
+ return new Widening();
+ }
+
+ @Override
+ public String toString() {
+ return "Cast.Widening";
+ }
+
+ @Override
+ public List<CompatibilityError> apply(final Schema input, final Schema
output) {
+ return fold.apply(input, output);
+ }
+
+ private static class Fold extends SchemaZipFold<List<CompatibilityError>> {
+
+ @Override
+ public List<CompatibilityError> accumulate(
+ List<CompatibilityError> left, List<CompatibilityError> right) {
+ return
ImmutableList.<CompatibilityError>builder().addAll(left).addAll(right).build();
+ }
+
+ @Override
+ public List<CompatibilityError> accept(
+ Context context, Optional<Field> left, Optional<Field> right) {
+ if (!left.isPresent() && !right.isPresent()) {
+ return Collections.emptyList();
+ } else if (left.isPresent() && !right.isPresent()) {
+ return Collections.emptyList();
+ } else if (!left.isPresent() && right.isPresent()) {
+ return Collections.singletonList(
+ CompatibilityError.create(context.path(), "Field is missing in
output schema"));
+ } else {
+ if (left.get().getNullable() && !right.get().getNullable()) {
+ return Collections.singletonList(
+ CompatibilityError.create(
+ context.path(), "Can't cast nullable field to non-nullable
field"));
+ }
+ }
+
+ return Collections.emptyList();
+ }
+
+ @Override
+ public List<CompatibilityError> accept(Context context, FieldType input,
FieldType output) {
+ TypeName inputType = input.getTypeName();
+ TypeName outputType = output.getTypeName();
+
+ boolean supertype = outputType.isSupertypeOf(inputType);
+
+ if (isIntegral(inputType) && isDecimal(outputType)) {
Review comment:
It can happen later, but I think the authoritative catalog of what is a
subtype/supertype and what can be coerced can live as top-level concepts, and
the transform just a quick helper to apply them.
In particular, it took me a second to understand why there are two branches
here. The first branch is "allowed automatic coercion" and the final return
below is the usual "no action required" subtyping.
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Issue Time Tracking
-------------------
Worklog Id: (was: 162654)
Time Spent: 4h 20m (was: 4h 10m)
> 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: Gleb Kanterov
> Priority: Major
> Time Spent: 4h 20m
> 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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