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https://issues.apache.org/jira/browse/BEAM-5918?focusedWorklogId=162651&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-162651
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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_r230858306
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/SchemaZipFold.java
##########
@@ -0,0 +1,155 @@
+/*
+ * 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.utils;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import java.io.Serializable;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Stream;
+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;
+
+/**
+ * Visitor that zips schemas, and accepts pairs of fields and their types.
+ *
+ * <p>Values returned by `accept` are accumulated.
+ */
+public abstract class SchemaZipFold<T> implements Serializable {
Review comment:
I understand this class, but maybe others won't love it vs nested switch
statements / static recursive functions. Out of curiosity does it not add some
allocation cost?
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Issue Time Tracking
-------------------
Worklog Id: (was: 162651)
Time Spent: 4h 10m (was: 4h)
> 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 10m
> 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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