PLUGIN-1939: Adding nullable split support in DB plugins.

database-commons/src/main/java/io/cdap/plugin/db/source/DataDrivenETLDBInputFormat.java

@@ -16,14 +16,18 @@
 
 package io.cdap.plugin.db.source;
 
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Strings;
 import com.google.common.base.Throwables;
+import com.google.common.collect.ImmutableList;
 import io.cdap.plugin.db.ConnectionConfigAccessor;
 import io.cdap.plugin.db.JDBCDriverShim;
 import io.cdap.plugin.db.NoOpCommitConnection;
 import io.cdap.plugin.db.TransactionIsolationLevel;
 import io.cdap.plugin.util.DBUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.mapreduce.InputSplit;
+import org.apache.hadoop.mapreduce.JobContext;
 import org.apache.hadoop.mapreduce.RecordReader;
 import org.apache.hadoop.mapreduce.TaskAttemptContext;
 import org.apache.hadoop.mapreduce.lib.db.DBConfiguration;
@@ -41,6 +45,7 @@
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.sql.Types;
+import java.util.List;
 import java.util.Properties;
 
 /**
@@ -64,6 +69,58 @@ public static void setInput(Configuration conf,
     new ConnectionConfigAccessor(conf).setAutoCommitEnabled(enableAutoCommit);
   }
 
+  /**
+   * A wrapper around the superclass getSplits method. This is required for testing,
+   * as mocking a method that calls its superclass implementation is challenging.
+   * This wrapper allows unit tests to override this method and mock the behavior of
+   * the superclass call, isolating the logic within the overridden getSplits method.
+   *
+   * @param job The job context.
+   * @return The list of input splits generated by the parent class.
+   * @throws IOException If an error occurs while getting the splits.
+   */
+  @VisibleForTesting
+  List<InputSplit> getBaseSplits(JobContext job) throws IOException {
+    return super.getSplits(job);
+  }
+
+  @Override
+  public List<InputSplit> getSplits(JobContext job) throws IOException {
+    List<InputSplit> splits = getBaseSplits(job);
+
+    // Handle the edge case where the base implementation returns no splits. In this scenario,
+    // create a single, all-encompassing split to ensure the job can proceed.
+    if (splits == null || splits.isEmpty()) {
+      return ImmutableList.<InputSplit>builder()
+          .add(new DataDrivenDBInputSplit("1=1", "1=1"))
+          .build();
+    }
+
+    // Check if a split for NULL values or an all-encompassing split ("1=1") already exists.
+    boolean shouldAddNullSplit = splits.stream()
+        .map(DataDrivenDBInputFormat.DataDrivenDBInputSplit.class::cast)
+        .map(DataDrivenDBInputFormat.DataDrivenDBInputSplit::getLowerClause)
+        .noneMatch(lowerClause ->
+            !Strings.isNullOrEmpty(lowerClause)
+                && (lowerClause.contains("IS NULL") || lowerClause.contains("1=1")));
+
+    if (shouldAddNullSplit) {
+      // Create a dedicated split to handle potential NULL values in the split-by column.
+      String splitByColumn = getDBConf().getInputOrderBy();
+      LOG.debug("No split found for NULL values. Adding a split for '{} IS NULL'.", splitByColumn);
+      String clause = String.format("%s IS NULL", splitByColumn);
+      InputSplit nullSplit =
+          new DataDrivenDBInputFormat.DataDrivenDBInputSplit(clause, clause);
+
+      return ImmutableList.<InputSplit>builder()
+          .addAll(splits)
+          .add(nullSplit)
+          .build();
+    }
+
+    return splits;
+  }
+
   @Override
   public Connection getConnection() {
     if (this.connection == null) {

database-commons/src/test/java/io/cdap/plugin/db/source/DataDrivenETLDBInputFormatTest.java

@@ -0,0 +1,121 @@
+/*
+ * Copyright © 2019 Cask Data, Inc.
+ *
+ * Licensed 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 io.cdap.plugin.db.source;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.hadoop.mapreduce.InputSplit;
+import org.apache.hadoop.mapreduce.JobContext;
+import org.apache.hadoop.mapreduce.lib.db.DBConfiguration;
+import org.apache.hadoop.mapreduce.lib.db.DataDrivenDBInputFormat;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.runners.MockitoJUnitRunner;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
+
+@RunWith(MockitoJUnitRunner.class)
+public class DataDrivenETLDBInputFormatTest {
+
+  @Mock
+  private JobContext mockJobContext;
+  @Mock
+  private DBConfiguration mockDbConfiguration;
+
+  private DataDrivenETLDBInputFormat inputFormat;
+
+  @Before
+  public void setUp() {
+    inputFormat = Mockito.spy(new DataDrivenETLDBInputFormat());
+    Mockito.doReturn(mockDbConfiguration).when(inputFormat).getDBConf();
+    Mockito.doReturn("id").when(mockDbConfiguration).getInputOrderBy();
+  }
+
+  @Test
+  public void testGetSplitsAddsNullSplit() throws IOException {
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit existingSplit =
+        new DataDrivenDBInputFormat.DataDrivenDBInputSplit("id >= 0", "id < 100");
+    List<InputSplit> initialSplits = ImmutableList.of(existingSplit);
+    Mockito.doReturn(initialSplits).when(inputFormat).getBaseSplits(mockJobContext);
+
+    List<InputSplit> finalSplits = inputFormat.getSplits(mockJobContext);
+
+    Assert.assertEquals("A new split for NULLs should be added", 2, finalSplits.size());
+
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit nullSplit =
+        (DataDrivenDBInputFormat.DataDrivenDBInputSplit) finalSplits.get(1);
+    Assert.assertEquals("id IS NULL", nullSplit.getLowerClause());
+    Assert.assertEquals("id IS NULL", nullSplit.getUpperClause());
+  }
+
+  @Test
+  public void testGetSplitsDoesNotAddNullSplitIfPresent() throws IOException {
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit existingSplit =
+        new DataDrivenDBInputFormat.DataDrivenDBInputSplit("id >= 0", "id < 100");
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit nullSplit =
+        new DataDrivenDBInputFormat.DataDrivenDBInputSplit("id IS NULL", "id IS NULL");
+    List<InputSplit> initialSplits = ImmutableList.of(existingSplit, nullSplit);
+
+    Mockito.doReturn(initialSplits).when(inputFormat).getBaseSplits(mockJobContext);
+
+    List<InputSplit> finalSplits = inputFormat.getSplits(mockJobContext);
+
+    Assert.assertEquals("Should not add a duplicate NULL split", 2, finalSplits.size());
+  }
+
+  @Test
+  public void testGetSplitsDoesNotAddNullSplitIfSelectAllPresent() throws IOException {
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit existingSplit =
+        new DataDrivenDBInputFormat.DataDrivenDBInputSplit("1=1", "1=1");
+    List<InputSplit> initialSplits = ImmutableList.of(existingSplit);
+
+    Mockito.doReturn(initialSplits).when(inputFormat).getBaseSplits(mockJobContext);
+
+    List<InputSplit> finalSplits = inputFormat.getSplits(mockJobContext);
+
+    Assert.assertEquals("Should not add a NULL split", 1, finalSplits.size());
+  }
+
+  @Test
+  public void testGetSplitsDoesNotAddNullSplitIfBaseReturnsNull() throws IOException {
+    Mockito.doReturn(null).when(inputFormat).getBaseSplits(mockJobContext);
+
+    List<InputSplit> finalSplits = inputFormat.getSplits(mockJobContext);
+    Assert.assertEquals("Should not add a NULL split", 1, finalSplits.size());
+
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit split =
+        (DataDrivenDBInputFormat.DataDrivenDBInputSplit) finalSplits.get(0);
+    Assert.assertEquals("1=1", split.getLowerClause());
+  }
+
+  @Test
+  public void testGetSplitsDoesNotAddNullSplitIfBaseReturnsEmptyList() throws IOException {
+    Mockito.doReturn(Collections.emptyList()).when(inputFormat).getBaseSplits(mockJobContext);
+
+    List<InputSplit> finalSplits = inputFormat.getSplits(mockJobContext);
+    Assert.assertEquals("Should not add a NULL split", 1, finalSplits.size());
+
+    DataDrivenDBInputFormat.DataDrivenDBInputSplit split =
+        (DataDrivenDBInputFormat.DataDrivenDBInputSplit) finalSplits.get(0);
+    Assert.assertEquals("1=1", split.getLowerClause());
+  }
+}