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Dataset API: Allow empty projection #24

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Jul 1, 2021
Merged

Dataset API: Allow empty projection #24

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4 changes: 1 addition & 3 deletions cpp/src/jni/dataset/jni_wrapper.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -590,9 +590,7 @@ JNIEXPORT jlong JNICALL Java_org_apache_arrow_dataset_jni_JniWrapper_createScann
JniAssertOkOrThrow(scanner_builder->Pool(pool));

std::vector<std::string> column_vector = ToStringVector(env, columns);
if (!column_vector.empty()) {
JniAssertOkOrThrow(scanner_builder->Project(column_vector));
}
JniAssertOkOrThrow(scanner_builder->Project(column_vector));
JniAssertOkOrThrow(scanner_builder->BatchSize(batch_size));
// initialize filters
jsize exprs_len = env->GetArrayLength(filter);
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21 changes: 21 additions & 0 deletions java/dataset/src/test/java/org/apache/arrow/dataset/file/TestFileSystemDataset.java
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Expand Up @@ -137,6 +137,27 @@ public void testParquetProjector() throws Exception {
AutoCloseables.close(factory);
}

@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(),
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