Fix expression result writing of arrays in Hadoop Ingestion (#15127)

processing/src/main/java/org/apache/druid/data/input/Rows.java

@@ -25,8 +25,10 @@ import com.google.common.primitives.Longs;
 import org.apache.druid.common.config.NullHandling;
 import org.apache.druid.java.util.common.StringUtils;
 import org.apache.druid.java.util.common.parsers.ParseException;
+import org.apache.druid.math.expr.Evals;
 
 import javax.annotation.Nullable;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -70,6 +72,8 @@ public final class Rows
     } else if (inputValue instanceof byte[]) {
       // convert byte[] to base64 encoded string
       return Collections.singletonList(StringUtils.encodeBase64String((byte[]) inputValue));
+    } else if (inputValue instanceof Object[]) {
+      return Arrays.stream((Object[]) inputValue).map(Evals::asString).collect(Collectors.toList());
     } else {
       return Collections.singletonList(String.valueOf(inputValue));
     }

processing/src/main/java/org/apache/druid/segment/transform/ExpressionTransform.java

@@ -31,7 +31,6 @@ import org.apache.druid.math.expr.Expr;
 import org.apache.druid.math.expr.ExprMacroTable;
 import org.apache.druid.math.expr.InputBindings;
 import org.apache.druid.math.expr.Parser;
-import org.apache.druid.segment.virtual.ExpressionSelectors;
 
 import java.util.List;
 import java.util.Objects;
@@ -111,9 +110,7 @@ public class ExpressionTransform implements Transform
     public List<String> evalDimension(Row row)
     {
       try {
-        return Rows.objectToStrings(
+        return Rows.objectToStrings(expr.eval(InputBindings.forRow(row)).valueOrDefault());
-            ExpressionSelectors.coerceEvalToObjectOrList(expr.eval(InputBindings.forRow(row)))
-        );
       }
       catch (Throwable t) {
         throw new ISE(t, "Could not transform dimension value for %s reason: %s", name, t.getMessage());

processing/src/test/java/org/apache/druid/segment/transform/TransformerTest.java

@@ -25,6 +25,8 @@ import org.apache.druid.common.config.NullHandling;
 import org.apache.druid.data.input.InputRow;
 import org.apache.druid.data.input.InputRowListPlusRawValues;
 import org.apache.druid.data.input.MapBasedInputRow;
+import org.apache.druid.data.input.MapBasedRow;
+import org.apache.druid.data.input.Row;
 import org.apache.druid.java.util.common.DateTimes;
 import org.apache.druid.java.util.common.parsers.ParseException;
 import org.apache.druid.query.expression.TestExprMacroTable;
@@ -37,6 +39,8 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
+import javax.annotation.Nullable;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
@@ -385,7 +389,7 @@ public class TransformerTest extends InitializedNullHandlingTest
     Assert.assertNotNull(actual);
     Assert.assertEquals(ImmutableList.of("dim"), actual.getDimensions());
     Assert.assertArrayEquals(new Object[]{1L, 2L, null, 3L}, (Object[]) actual.getRaw("dim"));
-    Assert.assertEquals(Arrays.asList("1", "2", "null", "3"), actual.getDimension("dim"));
+    Assert.assertArrayEquals(new String[]{"1", "2", null, "3"}, actual.getDimension("dim").toArray());
     Assert.assertEquals(row.getTimestamp(), actual.getTimestamp());
   }
 
@@ -412,9 +416,9 @@ public class TransformerTest extends InitializedNullHandlingTest
     Assert.assertEquals(2.3, (Double) raw[1], 0.00001);
     Assert.assertNull(raw[2]);
     Assert.assertEquals(3.4, (Double) raw[3], 0.00001);
-    Assert.assertEquals(
+    Assert.assertArrayEquals(
-        Arrays.asList("1.2000000476837158", "2.299999952316284", "null", "3.4000000953674316"),
+        new String[]{"1.2000000476837158", "2.299999952316284", null, "3.4000000953674316"},
-        actual.getDimension("dim")
+        actual.getDimension("dim").toArray()
     );
     Assert.assertEquals(row.getTimestamp(), actual.getTimestamp());
   }
@@ -441,7 +445,78 @@ public class TransformerTest extends InitializedNullHandlingTest
     Assert.assertEquals(2.3, (Double) raw[1], 0.0);
     Assert.assertNull(raw[2]);
     Assert.assertEquals(3.4, (Double) raw[3], 0.0);
-    Assert.assertEquals(Arrays.asList("1.2", "2.3", "null", "3.4"), actual.getDimension("dim"));
+    Assert.assertArrayEquals(new String[]{"1.2", "2.3", null, "3.4"}, actual.getDimension("dim").toArray());
     Assert.assertEquals(row.getTimestamp(), actual.getTimestamp());
   }
+
+  @Test
+  public void testTransformWithExpr()
+  {
+    final Transformer transformer = new Transformer(
+        new TransformSpec(
+            null,
+            ImmutableList.of(
+                new ExpressionTransform("dim", "array_slice(dim, 0, 5)", TestExprMacroTable.INSTANCE),
+                new ExpressionTransform("dim1", "array_slice(dim, 0, 1)", TestExprMacroTable.INSTANCE)
+            )
+        )
+    );
+    final List<String> dimList = ImmutableList.of("a", "b", "c", "d", "e", "f", "g");
+    final MapBasedRow row = new MapBasedRow(
+        DateTimes.nowUtc(),
+        ImmutableMap.of("dim", dimList)
+    );
+    Assert.assertEquals(row.getDimension("dim"), dimList);
+    Assert.assertEquals(row.getRaw("dim"), dimList);
+
+    final InputRow actualTranformedRow = transformer.transform(new InputRow()
+    {
+      @Override
+      public List<String> getDimensions()
+      {
+        return new ArrayList<>(row.getEvent().keySet());
+      }
+
+      @Override
+      public long getTimestampFromEpoch()
+      {
+        return 0;
+      }
+
+      @Override
+      public DateTime getTimestamp()
+      {
+        return row.getTimestamp();
+      }
+
+      @Override
+      public List<String> getDimension(String dimension)
+      {
+        return row.getDimension(dimension);
+      }
+
+      @Nullable
+      @Override
+      public Object getRaw(String dimension)
+      {
+        return row.getRaw(dimension);
+      }
+
+      @Nullable
+      @Override
+      public Number getMetric(String metric)
+      {
+        return row.getMetric(metric);
+      }
+
+      @Override
+      public int compareTo(Row o)
+      {
+        return row.compareTo(o);
+      }
+    });
+    Assert.assertEquals(actualTranformedRow.getDimension("dim"), dimList.subList(0, 5));
+    Assert.assertArrayEquals(dimList.subList(0, 5).toArray(), (Object[]) actualTranformedRow.getRaw("dim"));
+    Assert.assertArrayEquals(new Object[]{"a"}, actualTranformedRow.getDimension("dim1").toArray());
+  }
 }