Dataset API: Allow empty projection (apache#24)

zhztheplayer · Feb 28, 2022 · 6799b38 · 6799b38
1 parent 5b633c5
commit 6799b38
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Showing 2 changed files with 24 additions and 4 deletions.
diff --git a/cpp/src/jni/dataset/jni_wrapper.cc b/cpp/src/jni/dataset/jni_wrapper.cc
@@ -413,10 +413,9 @@ JNIEXPORT jlong JNICALL Java_org_apache_arrow_dataset_jni_JniWrapper_createScann
  std::shared_ptr<arrow::dataset::ScannerBuilder> scanner_builder =
  JniGetOrThrow(dataset->NewScan());
  JniAssertOkOrThrow(scanner_builder->Pool(pool));
- if (columns != nullptr) {
- std::vector<std::string> column_vector = ToStringVector(env, columns);
- JniAssertOkOrThrow(scanner_builder->Project(column_vector));
- }
+
+ std::vector<std::string> column_vector = ToStringVector(env, columns);
+ JniAssertOkOrThrow(scanner_builder->Project(column_vector));
  JniAssertOkOrThrow(scanner_builder->BatchSize(batch_size));
 
  auto scanner = JniGetOrThrow(scanner_builder->Finish());

diff --git a/java/dataset/src/test/java/org/apache/arrow/dataset/file/TestFileSystemDataset.java b/java/dataset/src/test/java/org/apache/arrow/dataset/file/TestFileSystemDataset.java
@@ -143,6 +143,27 @@ public void testParquetProjectSingleColumn() throws Exception {
  AutoCloseables.close(datum);
  }
 
+ @Test
+ public void testEmptyProjector() throws Exception {
+ ParquetWriteSupport writeSupport = ParquetWriteSupport.writeTempFile(AVRO_SCHEMA_USER, TMP.newFolder(), 1, "a",
+ 2, "b");
+
+ FileSystemDatasetFactory factory = new FileSystemDatasetFactory(rootAllocator(), NativeMemoryPool.getDefault(),
+ FileFormat.PARQUET, writeSupport.getOutputURI());
+ ScanOptions options = new ScanOptions(new String[]{}, Filter.EMPTY, 100);
+ Schema schema = inferResultSchemaFromFactory(factory, options);
+ List<ArrowRecordBatch> datum = collectResultFromFactory(factory, options);
+ org.apache.avro.Schema expectedSchema = truncateAvroSchema(writeSupport.getAvroSchema(), 0, 1);
+
+ assertSingleTaskProduced(factory, options);
+ assertEquals(0, schema.getFields().size());
+ assertEquals(1, datum.size());
+
+ AutoCloseables.close(datum);
+ AutoCloseables.close(factory);
+ }
+
+
  @Test
  public void testParquetBatchSize() throws Exception {
  ParquetWriteSupport writeSupport = ParquetWriteSupport.writeTempFile(AVRO_SCHEMA_USER, TMP.newFolder(),