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An example Calcite provider that reads CSV files

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you 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 org.apache.calcite.adapter.csv;

import org.apache.calcite.DataContext;
import org.apache.calcite.linq4j.AbstractEnumerable;
import org.apache.calcite.linq4j.Enumerable;
import org.apache.calcite.linq4j.Enumerator;
import org.apache.calcite.linq4j.QueryProvider;
import org.apache.calcite.linq4j.Queryable;
import org.apache.calcite.linq4j.tree.Expression;
import org.apache.calcite.plan.RelOptTable;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.type.RelProtoDataType;
import org.apache.calcite.schema.QueryableTable;
import org.apache.calcite.schema.SchemaPlus;
import org.apache.calcite.schema.Schemas;
import org.apache.calcite.schema.TranslatableTable;
import org.apache.calcite.util.Source;

import java.lang.reflect.Type;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Table based on a CSV file.
 */
public class CsvTranslatableTable extends CsvTable
    implements QueryableTable, TranslatableTable {
  /** Creates a CsvTable. */
  CsvTranslatableTable(Source source, RelProtoDataType protoRowType) {
    super(source, protoRowType);
  }

  public String toString() {
    return "CsvTranslatableTable";
  }

  /** Returns an enumerable over a given projection of the fields.
   *
   * 
Called from generated code. */
  public Enumerable project(final DataContext root,
      final int[] fields) {
    final AtomicBoolean cancelFlag = DataContext.Variable.CANCEL_FLAG.get(root);
    return new AbstractEnumerable() {
      public Enumerator enumerator() {
        return new CsvEnumerator<>(source, cancelFlag, fieldTypes, fields);
      }
    };
  }

  public Expression getExpression(SchemaPlus schema, String tableName,
      Class clazz) {
    return Schemas.tableExpression(schema, getElementType(), tableName, clazz);
  }

  public Type getElementType() {
    return Object[].class;
  }

  public  Queryable asQueryable(QueryProvider queryProvider,
      SchemaPlus schema, String tableName) {
    throw new UnsupportedOperationException();
  }

  public RelNode toRel(
      RelOptTable.ToRelContext context,
      RelOptTable relOptTable) {
    // Request all fields.
    final int fieldCount = relOptTable.getRowType().getFieldCount();
    final int[] fields = CsvEnumerator.identityList(fieldCount);
    return new CsvTableScan(context.getCluster(), relOptTable, this, fields);
  }
}

// End CsvTranslatableTable.java
    

    

    

            

    

            



    
    






    
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