Fix: external table regress allow demo text resolver to handle multiple fields

server/pxf-api/src/main/java/org/greenplum/pxf/api/examples/DemoTextResolver.java

@@ -23,11 +23,13 @@
 import org.greenplum.pxf.api.OneRow;
 import org.greenplum.pxf.api.io.DataType;
 
+import java.nio.charset.StandardCharsets;
 import java.util.LinkedList;
 import java.util.List;
 
 /**
- * Class that defines the serialization / deserialization of one record brought from the external input data.
+ * Class that defines the serialization / deserialization of one record brought
+ * from the external input data.
  * <p>
  * Demo implementation of resolver that returns text format
  */
@@ -57,13 +59,34 @@ public List<OneField> getFields(OneRow row) {
      */
     @Override
     public OneRow setFields(List<OneField> record) throws Exception {
-        // text row data is passed as a single field
-        if (record == null || record.size() != 1) {
-            throw new Exception("Unexpected record format, expected 1 field, found " +
-                    (record == null ? 0 : record.size()));
+        if (record == null || record.isEmpty()) {
+            throw new Exception("Unexpected record format, no fields provided");
         }
-        byte[] value = (byte[]) record.get(0).val;
-        // empty array means the end of input stream, return null to stop iterations
-        return value.length == 0 ? null : new OneRow(value);
+
+        // Legacy single-field end-of-stream marker (empty byte[]), keep behavior
+        if (record.size() == 1 && record.get(0).val instanceof byte[]) {
+            byte[] value = (byte[]) record.get(0).val;
+            if (value.length == 0) {
+                return null;
+            }
+            // Preserve legacy single-field behavior: return the bytes as-is
+            return new OneRow(value);
+        }
+
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < record.size(); i++) {
+            Object val = record.get(i).val;
+            if (val instanceof byte[]) {
+                sb.append(new String((byte[]) val, StandardCharsets.UTF_8));
+            } else if (val != null) {
+                sb.append(val.toString());
+            }
+            if (i < record.size() - 1) {
+                sb.append(',');
+            }
+        }
+        sb.append('\n');
+
+        return new OneRow(sb.toString().getBytes(StandardCharsets.UTF_8));
     }
 }

server/pxf-api/src/test/java/org/greenplum/pxf/api/DemoResolverTest.java

@@ -19,7 +19,6 @@
  * under the License.
  */
 
-
 import org.greenplum.pxf.api.examples.DemoResolver;
 import org.greenplum.pxf.api.examples.DemoTextResolver;
 import org.greenplum.pxf.api.model.RequestContext;
@@ -79,7 +78,7 @@ public void testSetTextData() throws Exception {
 
     @Test
     public void testSetEmptyTextData() throws Exception {
-        OneField field = new OneField(VARCHAR.getOID(), new byte[]{});
+        OneField field = new OneField(VARCHAR.getOID(), new byte[] {});
         OneRow output = textResolver.setFields(Collections.singletonList(field));
         assertNull(output);
     }
@@ -97,16 +96,17 @@ public void testSetTextDataEmptyInput() {
     }
 
     @Test
-    public void testSetTextDataManyElements() {
-        assertThrows(Exception.class,
-                () -> textResolver.setFields(Arrays.asList(field, field)));
+    public void testSetTextDataManyElements() throws Exception {
+        OneRow output = textResolver.setFields(Arrays.asList(field, field));
+        assertArrayEquals("value1,value2,value1,value2\n".getBytes(),
+                (byte[]) output.getData());
     }
 
     @Test
     public void testSetFieldsIsUnsupported() {
-      Exception e = assertThrows(UnsupportedOperationException.class,
+        Exception e = assertThrows(UnsupportedOperationException.class,
                 () -> customResolver.setFields(null));
 
-      assertEquals("Demo resolver does not support write operation", e.getMessage());
+        assertEquals("Demo resolver does not support write operation", e.getMessage());
     }
 }