parquet-cascading/src/main/java/parquet/cascading/SchemaIntersection.java

/**
 * Copyright 2012 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package parquet.cascading;

import parquet.schema.MessageType;
import parquet.schema.Type;

import cascading.tuple.Fields;

import java.util.List;
import java.util.ArrayList;

public class SchemaIntersection {

  private final MessageType requestedSchema;
  private final Fields sourceFields;

  public SchemaIntersection(MessageType fileSchema, Fields requestedFields) {
    if(requestedFields == Fields.UNKNOWN)
      requestedFields = Fields.ALL;

    Fields newFields = Fields.NONE;
    List<Type> newSchemaFields = new ArrayList<Type>();
    int schemaSize = fileSchema.getFieldCount();

    for (int i = 0; i < schemaSize; i++) {
      Type type = fileSchema.getType(i);
      Fields name = new Fields(type.getName());

      if(requestedFields.contains(name)) {
        newFields = newFields.append(name);
        newSchemaFields.add(type);
      }
    }

    this.sourceFields = newFields;
    this.requestedSchema = new MessageType(fileSchema.getName(), newSchemaFields);
  }

  public MessageType getRequestedSchema() {
    return requestedSchema;
  }

  public Fields getSourceFields() {
    return sourceFields;
  }
}