[BEAM-11460] Support reading Parquet files with unknown schema

CHANGES.md

@@ -58,6 +58,7 @@
 * ReadFromMongoDB/WriteToMongoDB will mask password in display_data (Python) ([BEAM-11444](https://issues.apache.org/jira/browse/BEAM-11444).)
 * Support for X source added (Java/Python) ([BEAM-X](https://issues.apache.org/jira/browse/BEAM-X)).
 * There is a new transform `ReadAllFromBigQuery` that can receive multiple requests to read data from BigQuery at pipeline runtime. See [PR 13170](https://github.com/apache/beam/pull/13170), and [BEAM-9650](https://issues.apache.org/jira/browse/BEAM-9650).
+* ParquetIO can now read files with an unknown schema. See [PR-13554](https://github.com/apache/beam/pull/13554) and ([BEAM-11460](https://issues.apache.org/jira/browse/BEAM-11460))
 
 ## New Features / Improvements
 

sdks/java/io/parquet/src/main/java/org/apache/beam/sdk/io/parquet/ParquetIO.java

@@ -18,6 +18,7 @@
 package org.apache.beam.sdk.io.parquet;
 
 import static java.lang.String.format;
+import static org.apache.parquet.Preconditions.checkArgument;
 import static org.apache.parquet.Preconditions.checkNotNull;
 import static org.apache.parquet.hadoop.ParquetFileWriter.Mode.OVERWRITE;
 
@@ -38,21 +39,30 @@
 import org.apache.beam.sdk.annotations.Experimental;
 import org.apache.beam.sdk.annotations.Experimental.Kind;
 import org.apache.beam.sdk.coders.AvroCoder;
+import org.apache.beam.sdk.coders.CannotProvideCoderException;
+import org.apache.beam.sdk.coders.Coder;
+import org.apache.beam.sdk.coders.CoderRegistry;
 import org.apache.beam.sdk.coders.StringUtf8Coder;
 import org.apache.beam.sdk.io.FileIO;
+import org.apache.beam.sdk.io.FileIO.ReadableFile;
 import org.apache.beam.sdk.io.fs.ResourceId;
 import org.apache.beam.sdk.io.hadoop.SerializableConfiguration;
+import org.apache.beam.sdk.io.parquet.ParquetIO.ReadFiles.ReadFn;
+import org.apache.beam.sdk.io.parquet.ParquetIO.ReadFiles.SplitReadFn;
 import org.apache.beam.sdk.io.range.OffsetRange;
 import org.apache.beam.sdk.options.ValueProvider;
 import org.apache.beam.sdk.transforms.Create;
 import org.apache.beam.sdk.transforms.DoFn;
 import org.apache.beam.sdk.transforms.PTransform;
 import org.apache.beam.sdk.transforms.ParDo;
+import org.apache.beam.sdk.transforms.SerializableFunction;
 import org.apache.beam.sdk.transforms.display.DisplayData;
 import org.apache.beam.sdk.transforms.splittabledofn.OffsetRangeTracker;
 import org.apache.beam.sdk.transforms.splittabledofn.RestrictionTracker;
 import org.apache.beam.sdk.values.PBegin;
 import org.apache.beam.sdk.values.PCollection;
+import org.apache.beam.sdk.values.TypeDescriptors;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.annotations.VisibleForTesting;
 import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.ImmutableSet;
 import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
 import org.apache.hadoop.conf.Configuration;
@@ -152,6 +162,44 @@
  * *
  * }</pre>
  *
+ * <h3>Reading records of an unknown schema</h3>
+ *
+ * <p>To read records from files whose schema is unknown at pipeline construction time or differs
+ * between files, use {@link #parseGenericRecords(SerializableFunction)} - in this case, you will
+ * need to specify a parsing function for converting each {@link GenericRecord} into a value of your
+ * custom type.
+ *
+ * <p>For example:
+ *
+ * <pre>{@code
+ * Pipeline p = ...;
+ *
+ * PCollection<Foo> records =
+ *     p.apply(
+ *       ParquetIO.parseGenericRecords(
+ *           new SerializableFunction<GenericRecord, Foo>() {
+ *               public Foo apply(GenericRecord record) {
+ *                   // If needed, access the schema of the record using record.getSchema()
+ *                   return ...;
+ *               }
+ *           })
+ *           .setFilePattern(...));
+ *
+ * // For reading from files
+ *  PCollection<FileIO.ReadableFile> files = p.apply(...);
+ *
+ *  PCollection<Foo> records =
+ *     files
+ *       .apply(
+ *           ParquetIO.parseFilesGenericRecords(
+ *               new SerializableFunction<GenericRecord, Foo>() {
+ *                   public Foo apply(GenericRecord record) {
+ *                       // If needed, access the schema of the record using record.getSchema()
+ *                       return ...;
+ *                   }
+ *           }));
+ * }</pre>
+ *
  * <h3>Writing Parquet files</h3>
  *
  * <p>{@link ParquetIO.Sink} allows you to write a {@link PCollection} of {@link GenericRecord} into
@@ -202,7 +250,30 @@ public static Read read(Schema schema) {
    */
   public static ReadFiles readFiles(Schema schema) {
     return new AutoValue_ParquetIO_ReadFiles.Builder()
+        .setSplittable(false)
         .setSchema(schema)
+        .build();
+  }
+
+  /**
+   * Reads {@link GenericRecord} from a Parquet file (or multiple Parquet files matching the
+   * pattern) and converts to user defined type using provided parseFn.
+   */
+  public static <T> Parse<T> parseGenericRecords(SerializableFunction<GenericRecord, T> parseFn) {
+    return new AutoValue_ParquetIO_Parse.Builder<T>()
+        .setParseFn(parseFn)
+        .setSplittable(false)
+        .build();
+  }
+
+  /**
+   * Reads {@link GenericRecord} from Parquet files and converts to user defined type using provided
+   * {@code parseFn}.
+   */
+  public static <T> ParseFiles<T> parseFilesGenericRecords(
+      SerializableFunction<GenericRecord, T> parseFn) {
+    return new AutoValue_ParquetIO_ParseFiles.Builder<T>()
+        .setParseFn(parseFn)
         .setSplittable(false)
         .build();
   }
@@ -300,6 +371,121 @@ public void populateDisplayData(DisplayData.Builder builder) {
     }
   }
 
+  /** Implementation of {@link #parseGenericRecords(SerializableFunction)}. */
+  @AutoValue
+  public abstract static class Parse<T> extends PTransform<PBegin, PCollection<T>> {
+    abstract @Nullable ValueProvider<String> getFilepattern();
+
+    abstract SerializableFunction<GenericRecord, T> getParseFn();
+
+    abstract boolean isSplittable();
+
+    abstract Builder<T> toBuilder();
+
+    @AutoValue.Builder
+    abstract static class Builder<T> {
+      abstract Builder<T> setFilepattern(ValueProvider<String> inputFiles);
+
+      abstract Builder<T> setParseFn(SerializableFunction<GenericRecord, T> parseFn);
+
+      abstract Builder<T> setSplittable(boolean splittable);
+
+      abstract Parse<T> build();
+    }
+
+    public Parse<T> from(ValueProvider<String> inputFiles) {
+      return toBuilder().setFilepattern(inputFiles).build();
+    }
+
+    public Parse<T> from(String inputFiles) {
+      return from(ValueProvider.StaticValueProvider.of(inputFiles));
+    }
+
+    public Parse<T> withSplit() {
+      return toBuilder().setSplittable(true).build();
+    }
+
+    @Override
+    public PCollection<T> expand(PBegin input) {
+      checkNotNull(getFilepattern(), "Filepattern cannot be null.");
+      return input
+          .apply("Create filepattern", Create.ofProvider(getFilepattern(), StringUtf8Coder.of()))
+          .apply(FileIO.matchAll())
+          .apply(FileIO.readMatches())
+          .apply(
+              parseFilesGenericRecords(getParseFn())
+                  .toBuilder()
+                  .setSplittable(isSplittable())
+                  .build());
+    }
+  }
+
+  /** Implementation of {@link #parseFilesGenericRecords(SerializableFunction)}. */
+  @AutoValue
+  public abstract static class ParseFiles<T>
+      extends PTransform<PCollection<FileIO.ReadableFile>, PCollection<T>> {
+
+    abstract SerializableFunction<GenericRecord, T> getParseFn();
+
+    abstract boolean isSplittable();
+
+    abstract Builder<T> toBuilder();
+
+    @AutoValue.Builder
+    abstract static class Builder<T> {
+      abstract Builder<T> setParseFn(SerializableFunction<GenericRecord, T> parseFn);
+
+      abstract Builder<T> setSplittable(boolean split);
+
+      abstract ParseFiles<T> build();
+    }
+
+    public ParseFiles<T> withSplit() {
+      return toBuilder().setSplittable(true).build();
+    }
+
+    @Override
+    public PCollection<T> expand(PCollection<ReadableFile> input) {
+      checkArgument(!isGenericRecordOutput(), "Parse can't be used for reading as GenericRecord.");
+
+      PCollection<T> parsedRecords =
+          isSplittable()
+              ? input.apply(ParDo.of(new SplitReadFn<>(null, null, getParseFn())))
+              : input.apply(ParDo.of(new ReadFn<>(null, getParseFn())));
+
+      return parsedRecords.setCoder(inferCoder(input.getPipeline().getCoderRegistry()));
+    }
+
+    /** Returns true if expected output is {@code PCollection<GenericRecord>}. */
+    private boolean isGenericRecordOutput() {
+      String outputType = TypeDescriptors.outputOf(getParseFn()).getType().getTypeName();
+      return outputType.equals(GenericRecord.class.getTypeName());
+    }
+
+    /**
+     * Identifies the {@code Coder} to be used for the output PCollection.
+     *
+     * <p>Returns {@link AvroCoder} if expected output is {@link GenericRecord}.
+     *
+     * @param coderRegistry the {@link org.apache.beam.sdk.Pipeline}'s CoderRegistry to identify
+     *     Coder for expected output type of {@link #getParseFn()}
+     */
+    private Coder<T> inferCoder(CoderRegistry coderRegistry) {
+      if (isGenericRecordOutput()) {
+        throw new IllegalArgumentException("Parse can't be used for reading as GenericRecord.");
+      }
+
+      // If not GenericRecord infer it from ParseFn.
+      try {
+        return coderRegistry.getCoder(TypeDescriptors.outputOf(getParseFn()));
+      } catch (CannotProvideCoderException e) {
+        throw new IllegalArgumentException(
+            "Unable to infer coder for output of parseFn. Specify it explicitly using withCoder().",
+            e);
+      }
+    }
+  }
+
   /** Implementation of {@link #readFiles(Schema)}. */
   @AutoValue
   public abstract static class ReadFiles
@@ -357,26 +543,35 @@ public PCollection<GenericRecord> expand(PCollection<FileIO.ReadableFile> input)
       if (isSplittable()) {
         Schema coderSchema = getProjectionSchema() == null ? getSchema() : getEncoderSchema();
         return input
-            .apply(ParDo.of(new SplitReadFn(getAvroDataModel(), getProjectionSchema())))
+            .apply(
+                ParDo.of(
+                    new SplitReadFn<>(
+                        getAvroDataModel(),
+                        getProjectionSchema(),
+                        GenericRecordPassthroughFn.create())))
             .setCoder(AvroCoder.of(coderSchema));
       }
       return input
-          .apply(ParDo.of(new ReadFn(getAvroDataModel())))
+          .apply(ParDo.of(new ReadFn<>(getAvroDataModel(), GenericRecordPassthroughFn.create())))
           .setCoder(AvroCoder.of(getSchema()));
     }
 
     @DoFn.BoundedPerElement
-    static class SplitReadFn extends DoFn<FileIO.ReadableFile, GenericRecord> {
+    static class SplitReadFn<T> extends DoFn<FileIO.ReadableFile, T> {
       private Class<? extends GenericData> modelClass;
       private static final Logger LOG = LoggerFactory.getLogger(SplitReadFn.class);
       private String requestSchemaString;
       // Default initial splitting the file into blocks of 64MB. Unit of SPLIT_LIMIT is byte.
       private static final long SPLIT_LIMIT = 64000000;
 
-      SplitReadFn(GenericData model, Schema requestSchema) {
+      private final SerializableFunction<GenericRecord, T> parseFn;
+
+      SplitReadFn(
+          GenericData model, Schema requestSchema, SerializableFunction<GenericRecord, T> parseFn) {
 
         this.modelClass = model != null ? model.getClass() : null;
         this.requestSchemaString = requestSchema != null ? requestSchema.toString() : null;
+        this.parseFn = checkNotNull(parseFn, "GenericRecord parse function can't be null");
       }
 
       ParquetFileReader getParquetFileReader(FileIO.ReadableFile file) throws Exception {
@@ -388,7 +583,7 @@ ParquetFileReader getParquetFileReader(FileIO.ReadableFile file) throws Exceptio
       public void processElement(
           @Element FileIO.ReadableFile file,
           RestrictionTracker<OffsetRange, Long> tracker,
-          OutputReceiver<GenericRecord> outputReceiver)
+          OutputReceiver<T> outputReceiver)
           throws Exception {
         LOG.debug(
             "start "
@@ -468,7 +663,7 @@ record = recordReader.read();
                     file.toString());
                 continue;
               }
-              outputReceiver.output(record);
+              outputReceiver.output(parseFn.apply(record));
             } catch (RuntimeException e) {
 
               throw new ParquetDecodingException(
@@ -618,12 +813,15 @@ public Progress getProgress() {
       }
     }
 
-    static class ReadFn extends DoFn<FileIO.ReadableFile, GenericRecord> {
+    static class ReadFn<T> extends DoFn<FileIO.ReadableFile, T> {
 
       private Class<? extends GenericData> modelClass;
 
-      ReadFn(GenericData model) {
+      private final SerializableFunction<GenericRecord, T> parseFn;
+
+      ReadFn(GenericData model, SerializableFunction<GenericRecord, T> parseFn) {
         this.modelClass = model != null ? model.getClass() : null;
+        this.parseFn = checkNotNull(parseFn, "GenericRecord parse function is null");
       }
 
       @ProcessElement
@@ -647,7 +845,7 @@ public void processElement(ProcessContext processContext) throws Exception {
         try (ParquetReader<GenericRecord> reader = builder.build()) {
           GenericRecord read;
           while ((read = reader.read()) != null) {
-            processContext.output(read);
+            processContext.output(parseFn.apply(read));
           }
         }
       }
@@ -838,6 +1036,25 @@ public void close() throws IOException {
     }
   }
 
+  /**
+   * Passthrough function to provide seamless backward compatibility to ParquetIO's functionality.
+   */
+  @VisibleForTesting
+  static class GenericRecordPassthroughFn
+      implements SerializableFunction<GenericRecord, GenericRecord> {
+
+    private static final GenericRecordPassthroughFn singleton = new GenericRecordPassthroughFn();
+
+    static GenericRecordPassthroughFn create() {
+      return singleton;
+    }
+
+    @Override
+    public GenericRecord apply(GenericRecord input) {
+      return input;
+    }
+  }
+
   /** Disallow construction of utility class. */
   private ParquetIO() {}
 }