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https://issues.apache.org/jira/browse/BEAM-5427?focusedWorklogId=150954&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-150954
]
ASF GitHub Bot logged work on BEAM-5427:
----------------------------------------
Author: ASF GitHub Bot
Created on: 03/Oct/18 22:14
Start Date: 03/Oct/18 22:14
Worklog Time Spent: 10m
Work Description: swegner closed pull request #6439: [BEAM-5427] Fix and
update sample code for CombineFn.
URL: https://github.com/apache/beam/pull/6439
This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:
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diff --git
a/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java
b/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java
index 2c65f94d09a..20314fcba3c 100644
--- a/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java
+++ b/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java
@@ -254,10 +254,26 @@ private Combine() {
*
* <pre>{@code
* public class AverageFn extends CombineFn<Integer, AverageFn.Accum,
Double> {
- * public static class Accum {
+ * public static class Accum implements Serializable {
* int sum = 0;
* int count = 0;
+ *
+ * {@literal@}Override
+ * public boolean equals(Object other) {
+ * if (other == null) return false;
+ * if (other == this) return true;
+ * if (!(other instanceof Accum))return false;
+ *
+ *
+ * Accum o = (Accum)other;
+ * if (this.sum != o.sum || this.count != o.count) {
+ * return false;
+ * } else {
+ * return true;
+ * }
+ * }
* }
+ *
* public Accum createAccumulator() {
* return new Accum();
* }
@@ -289,6 +305,24 @@ private Combine() {
* arbitrary tree structure. Commutativity is required because any order of
the input values is
* ignored when breaking up input values into groups.
*
+ * <h3>Note on Data Encoding</h3>
+ *
+ * <p>Some form of data encoding is required when using custom types in a
CombineFn which do not
+ * have well-known coders. The sample code above uses a custom Accumulator
which gets coder by
+ * implementing {@link java.io.Serializable}. By doing this, we are relying
on the generic {@link
+ * org.apache.beam.sdk.coders.CoderProvider}, which is able to provide a
coder for any {@link
+ * java.io.Serializable} if applicable. In cases where {@link
java.io.Serializable} is not
+ * efficient, or inapplicable, in general there are two alternatives for
encoding:
+ *
+ * <ul>
+ * <li>Default {@link org.apache.beam.sdk.coders.CoderRegistry}. For
example, implement a coder
+ * class explicitly and use the {@code @DefaultCoder} tag. See the
{@link
+ * org.apache.beam.sdk.coders.CoderRegistry} for the numerous ways in
which to bind a type
+ * to a coder.
+ * <li>CombineFn specific way. While extending CombineFn, overwrite both
{@link
+ * #getAccumulatorCoder} and {@link #getDefaultOutputCoder}.
+ * </ul>
+ *
* @param <InputT> type of input values
* @param <AccumT> type of mutable accumulator values
* @param <OutputT> type of output values
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Issue Time Tracking
-------------------
Worklog Id: (was: 150954)
Time Spent: 3h 50m (was: 3h 40m)
> Fix sample code (AverageFn) in Combine.java
> -------------------------------------------
>
> Key: BEAM-5427
> URL: https://issues.apache.org/jira/browse/BEAM-5427
> Project: Beam
> Issue Type: Improvement
> Components: examples-java
> Reporter: Ruoyun Huang
> Assignee: Ruoyun Huang
> Priority: Minor
> Time Spent: 3h 50m
> Remaining Estimate: 0h
>
> Sample code missing coder.
> In its current state, job run fails with Coder missing error.
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