[GitHub] [beam] kennknowles commented on a diff in pull request #17070: Handle changing schemas in Storage API sink

[GitBox <gi...@apache.org>]

kennknowles commented on code in PR #17070:
URL: https://github.com/apache/beam/pull/17070#discussion_r846065333


##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/CreateTableDestinations.java:
##########
@@ -0,0 +1,132 @@
+/*
+ * 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.io.gcp.bigquery;
+
+import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import com.google.api.services.bigquery.model.TableSchema;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.Write.CreateDisposition;
+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.PCollectionView;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Supplier;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Lists;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+
+/**
+ * Creates any tables needed before performing streaming writes to the tables. This is a side-effect
+ * {@link DoFn}, and returns the original collection unchanged.
+ */
+public class CreateTableDestinations<DestinationT, ElementT>
+    extends PTransform<
+        PCollection<KV<DestinationT, ElementT>>, PCollection<KV<DestinationT, ElementT>>> {
+  private final CreateDisposition createDisposition;
+  private final BigQueryServices bqServices;
+  private final DynamicDestinations<?, DestinationT> dynamicDestinations;
+  @Nullable private final String kmsKey;
+
+  /**
+   * The list of tables created so far, so we don't try the creation each time.
+   *
+   * <p>TODO: We should put a bound on memory usage of this. Use guava cache instead.
+   */
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      DynamicDestinations<?, DestinationT> dynamicDestinations) {
+    this(createDisposition, new BigQueryServicesImpl(), dynamicDestinations, null);
+  }
+
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      BigQueryServices bqServices,
+      DynamicDestinations<?, DestinationT> dynamicDestinations,
+      @Nullable String kmsKey) {
+    this.createDisposition = createDisposition;
+    this.bqServices = bqServices;
+    this.dynamicDestinations = dynamicDestinations;
+    this.kmsKey = kmsKey;
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withKmsKey(String kmsKey) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withTestServices(BigQueryServices bqServices) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  @Override
+  public PCollection<KV<DestinationT, ElementT>> expand(
+      PCollection<KV<DestinationT, ElementT>> input) {
+    List<PCollectionView<?>> sideInputs = Lists.newArrayList();
+    sideInputs.addAll(dynamicDestinations.getSideInputs());
+
+    return input.apply("CreateTables", ParDo.of(new CreateTablesFn()).withSideInputs(sideInputs));
+  }
+
+  private class CreateTablesFn
+      extends DoFn<KV<DestinationT, ElementT>, KV<DestinationT, ElementT>> {
+    private Map<DestinationT, TableDestination> destinations = Maps.newHashMap();
+
+    @StartBundle
+    public void startBundle() {
+      destinations = Maps.newHashMap();
+    }
+
+    @ProcessElement
+    @SuppressWarnings({
+      "nullness" // TODO(https://issues.apache.org/jira/browse/BEAM-10402)
+    })
+    public void processElement(
+        ProcessContext context,
+        @Element KV<DestinationT, ElementT> element,
+        OutputReceiver<KV<DestinationT, ElementT>> o) {
+      dynamicDestinations.setSideInputAccessorFromProcessContext(context);
+      destinations.computeIfAbsent(
+          element.getKey(),
+          dest -> {
+            TableDestination tableDestination1 = dynamicDestinations.getTable(dest);

Review Comment:
   This variable should be `@Nullable`, clearly since you check it in the next line. And you can use `checkArgumentNotNull` to safely convert it to a non-null typed variable.



##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/CreateTableDestinations.java:
##########
@@ -0,0 +1,132 @@
+/*
+ * 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.io.gcp.bigquery;
+
+import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import com.google.api.services.bigquery.model.TableSchema;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.Write.CreateDisposition;
+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.PCollectionView;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Supplier;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Lists;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+
+/**
+ * Creates any tables needed before performing streaming writes to the tables. This is a side-effect
+ * {@link DoFn}, and returns the original collection unchanged.
+ */
+public class CreateTableDestinations<DestinationT, ElementT>
+    extends PTransform<
+        PCollection<KV<DestinationT, ElementT>>, PCollection<KV<DestinationT, ElementT>>> {
+  private final CreateDisposition createDisposition;
+  private final BigQueryServices bqServices;
+  private final DynamicDestinations<?, DestinationT> dynamicDestinations;
+  @Nullable private final String kmsKey;
+
+  /**
+   * The list of tables created so far, so we don't try the creation each time.
+   *
+   * <p>TODO: We should put a bound on memory usage of this. Use guava cache instead.
+   */
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      DynamicDestinations<?, DestinationT> dynamicDestinations) {
+    this(createDisposition, new BigQueryServicesImpl(), dynamicDestinations, null);
+  }
+
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      BigQueryServices bqServices,
+      DynamicDestinations<?, DestinationT> dynamicDestinations,
+      @Nullable String kmsKey) {
+    this.createDisposition = createDisposition;
+    this.bqServices = bqServices;
+    this.dynamicDestinations = dynamicDestinations;
+    this.kmsKey = kmsKey;
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withKmsKey(String kmsKey) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withTestServices(BigQueryServices bqServices) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  @Override
+  public PCollection<KV<DestinationT, ElementT>> expand(
+      PCollection<KV<DestinationT, ElementT>> input) {
+    List<PCollectionView<?>> sideInputs = Lists.newArrayList();
+    sideInputs.addAll(dynamicDestinations.getSideInputs());
+
+    return input.apply("CreateTables", ParDo.of(new CreateTablesFn()).withSideInputs(sideInputs));
+  }
+
+  private class CreateTablesFn
+      extends DoFn<KV<DestinationT, ElementT>, KV<DestinationT, ElementT>> {
+    private Map<DestinationT, TableDestination> destinations = Maps.newHashMap();
+
+    @StartBundle
+    public void startBundle() {
+      destinations = Maps.newHashMap();
+    }
+
+    @ProcessElement
+    @SuppressWarnings({
+      "nullness" // TODO(https://issues.apache.org/jira/browse/BEAM-10402)
+    })
+    public void processElement(
+        ProcessContext context,
+        @Element KV<DestinationT, ElementT> element,
+        OutputReceiver<KV<DestinationT, ElementT>> o) {
+      dynamicDestinations.setSideInputAccessorFromProcessContext(context);
+      destinations.computeIfAbsent(
+          element.getKey(),
+          dest -> {
+            TableDestination tableDestination1 = dynamicDestinations.getTable(dest);
+            checkArgument(
+                tableDestination1 != null,
+                "DynamicDestinations.getTable() may not return null, "

Review Comment:
   Didn't click through because GitHub isn't that friendly for it, but is `getTable` result marked `@Nullable` or not?



##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/CreateTableDestinations.java:
##########
@@ -0,0 +1,132 @@
+/*
+ * 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.io.gcp.bigquery;
+
+import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import com.google.api.services.bigquery.model.TableSchema;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.Write.CreateDisposition;
+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.PCollectionView;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Supplier;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Lists;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+
+/**
+ * Creates any tables needed before performing streaming writes to the tables. This is a side-effect
+ * {@link DoFn}, and returns the original collection unchanged.
+ */
+public class CreateTableDestinations<DestinationT, ElementT>
+    extends PTransform<
+        PCollection<KV<DestinationT, ElementT>>, PCollection<KV<DestinationT, ElementT>>> {
+  private final CreateDisposition createDisposition;
+  private final BigQueryServices bqServices;
+  private final DynamicDestinations<?, DestinationT> dynamicDestinations;
+  @Nullable private final String kmsKey;
+
+  /**
+   * The list of tables created so far, so we don't try the creation each time.

Review Comment:
   This comment seems to be on the wrong element.



##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/CreateTableDestinations.java:
##########
@@ -0,0 +1,132 @@
+/*
+ * 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.io.gcp.bigquery;
+
+import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import com.google.api.services.bigquery.model.TableSchema;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.Write.CreateDisposition;
+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.PCollectionView;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Supplier;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Lists;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+
+/**
+ * Creates any tables needed before performing streaming writes to the tables. This is a side-effect
+ * {@link DoFn}, and returns the original collection unchanged.

Review Comment:
   Would it make sense instead to return the tables created? Or, two outputs:
   
   1. PCollection of elements where it is now safe to write them to their destination table.
   2. PCollection of tables that have been created
   
   I assume the design currently is so the downstream stuff blocks on elements arriving in PCollection 1?



##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/CreateTableDestinations.java:
##########
@@ -0,0 +1,132 @@
+/*
+ * 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.io.gcp.bigquery;
+
+import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import com.google.api.services.bigquery.model.TableSchema;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.Write.CreateDisposition;
+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.PCollectionView;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Supplier;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Lists;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+
+/**
+ * Creates any tables needed before performing streaming writes to the tables. This is a side-effect
+ * {@link DoFn}, and returns the original collection unchanged.
+ */
+public class CreateTableDestinations<DestinationT, ElementT>
+    extends PTransform<
+        PCollection<KV<DestinationT, ElementT>>, PCollection<KV<DestinationT, ElementT>>> {
+  private final CreateDisposition createDisposition;
+  private final BigQueryServices bqServices;
+  private final DynamicDestinations<?, DestinationT> dynamicDestinations;
+  @Nullable private final String kmsKey;
+
+  /**
+   * The list of tables created so far, so we don't try the creation each time.
+   *
+   * <p>TODO: We should put a bound on memory usage of this. Use guava cache instead.
+   */
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      DynamicDestinations<?, DestinationT> dynamicDestinations) {
+    this(createDisposition, new BigQueryServicesImpl(), dynamicDestinations, null);
+  }
+
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      BigQueryServices bqServices,
+      DynamicDestinations<?, DestinationT> dynamicDestinations,
+      @Nullable String kmsKey) {
+    this.createDisposition = createDisposition;
+    this.bqServices = bqServices;
+    this.dynamicDestinations = dynamicDestinations;
+    this.kmsKey = kmsKey;
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withKmsKey(String kmsKey) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withTestServices(BigQueryServices bqServices) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  @Override
+  public PCollection<KV<DestinationT, ElementT>> expand(
+      PCollection<KV<DestinationT, ElementT>> input) {
+    List<PCollectionView<?>> sideInputs = Lists.newArrayList();
+    sideInputs.addAll(dynamicDestinations.getSideInputs());
+
+    return input.apply("CreateTables", ParDo.of(new CreateTablesFn()).withSideInputs(sideInputs));
+  }
+
+  private class CreateTablesFn
+      extends DoFn<KV<DestinationT, ElementT>, KV<DestinationT, ElementT>> {
+    private Map<DestinationT, TableDestination> destinations = Maps.newHashMap();
+
+    @StartBundle
+    public void startBundle() {
+      destinations = Maps.newHashMap();
+    }
+
+    @ProcessElement
+    @SuppressWarnings({
+      "nullness" // TODO(https://issues.apache.org/jira/browse/BEAM-10402)

Review Comment:
   Why add this to new code? Is there something that cannot be easily made nullness-correct? At least localize it to a specific line / declaration.



##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigquery/CreateTableDestinations.java:
##########
@@ -0,0 +1,132 @@
+/*
+ * 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.io.gcp.bigquery;
+
+import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;
+
+import com.google.api.services.bigquery.model.TableSchema;
+import java.util.List;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.io.gcp.bigquery.BigQueryIO.Write.CreateDisposition;
+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.PCollectionView;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Supplier;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Lists;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+
+/**
+ * Creates any tables needed before performing streaming writes to the tables. This is a side-effect
+ * {@link DoFn}, and returns the original collection unchanged.
+ */
+public class CreateTableDestinations<DestinationT, ElementT>
+    extends PTransform<
+        PCollection<KV<DestinationT, ElementT>>, PCollection<KV<DestinationT, ElementT>>> {
+  private final CreateDisposition createDisposition;
+  private final BigQueryServices bqServices;
+  private final DynamicDestinations<?, DestinationT> dynamicDestinations;
+  @Nullable private final String kmsKey;
+
+  /**
+   * The list of tables created so far, so we don't try the creation each time.
+   *
+   * <p>TODO: We should put a bound on memory usage of this. Use guava cache instead.
+   */
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      DynamicDestinations<?, DestinationT> dynamicDestinations) {
+    this(createDisposition, new BigQueryServicesImpl(), dynamicDestinations, null);
+  }
+
+  public CreateTableDestinations(
+      CreateDisposition createDisposition,
+      BigQueryServices bqServices,
+      DynamicDestinations<?, DestinationT> dynamicDestinations,
+      @Nullable String kmsKey) {
+    this.createDisposition = createDisposition;
+    this.bqServices = bqServices;
+    this.dynamicDestinations = dynamicDestinations;
+    this.kmsKey = kmsKey;
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withKmsKey(String kmsKey) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  CreateTableDestinations<DestinationT, ElementT> withTestServices(BigQueryServices bqServices) {
+    return new CreateTableDestinations<>(
+        createDisposition, bqServices, dynamicDestinations, kmsKey);
+  }
+
+  @Override
+  public PCollection<KV<DestinationT, ElementT>> expand(
+      PCollection<KV<DestinationT, ElementT>> input) {
+    List<PCollectionView<?>> sideInputs = Lists.newArrayList();
+    sideInputs.addAll(dynamicDestinations.getSideInputs());
+
+    return input.apply("CreateTables", ParDo.of(new CreateTablesFn()).withSideInputs(sideInputs));
+  }
+
+  private class CreateTablesFn
+      extends DoFn<KV<DestinationT, ElementT>, KV<DestinationT, ElementT>> {
+    private Map<DestinationT, TableDestination> destinations = Maps.newHashMap();
+
+    @StartBundle
+    public void startBundle() {
+      destinations = Maps.newHashMap();
+    }
+
+    @ProcessElement
+    @SuppressWarnings({
+      "nullness" // TODO(https://issues.apache.org/jira/browse/BEAM-10402)
+    })
+    public void processElement(
+        ProcessContext context,
+        @Element KV<DestinationT, ElementT> element,
+        OutputReceiver<KV<DestinationT, ElementT>> o) {
+      dynamicDestinations.setSideInputAccessorFromProcessContext(context);
+      destinations.computeIfAbsent(
+          element.getKey(),
+          dest -> {
+            TableDestination tableDestination1 = dynamicDestinations.getTable(dest);
+            checkArgument(
+                tableDestination1 != null,
+                "DynamicDestinations.getTable() may not return null, "
+                    + "but %s returned null for destination %s",
+                dynamicDestinations,
+                dest);
+            Supplier<TableSchema> schemaSupplier = () -> dynamicDestinations.getSchema(dest);
+            return CreateTableHelpers.possiblyCreateTable(

Review Comment:
   Is `computeIfAbsent` better than an `if` statement here? Seeing it used primarily for side effects, particularly side effects on another storage system, seems like it would be better expressed as an imperative block than this quasi-functional style.



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