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core module for querydsl
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/*
 * Copyright 2020, The Querydsl Team (http://www.querydsl.com/team)
 *
 * 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 com.querydsl.core.group;

import com.mysema.commons.lang.CloseableIterator;
import com.querydsl.core.FetchableQuery;
import com.querydsl.core.Tuple;
import com.querydsl.core.types.Expression;
import com.querydsl.core.types.FactoryExpression;
import com.querydsl.core.types.FactoryExpressionUtils;
import com.querydsl.core.types.Projections;
import com.querydsl.core.util.TupleUtils;
import java.util.Collection;
import java.util.Objects;
import java.util.function.Supplier;

/**
 * Provides aggregated results as a collection
 *
 * @param  Key type
 * @param  Value type
 * @param  Concrete collection type
 * @author Jan-Willem Gmelig Meyling
 */
public class GroupByGenericCollection>
    extends AbstractGroupByTransformer {

  private final Supplier resultFactory;

  GroupByGenericCollection(
      Supplier resultFactory, Expression key, Expression... expressions) {
    super(key, expressions);
    this.resultFactory = resultFactory;
  }

  @Override
  public RES transform(FetchableQuery query) {
    // create groups
    FactoryExpression expr = FactoryExpressionUtils.wrap(Projections.tuple(expressions));
    boolean hasGroups = false;
    for (Expression e : expr.getArgs()) {
      hasGroups |= e instanceof GroupExpression;
    }
    if (hasGroups) {
      expr = withoutGroupExpressions(expr);
    }
    final CloseableIterator iter = query.select(expr).iterate();

    RES list = resultFactory.get();
    GroupImpl group = null;
    K groupId = null;
    while (iter.hasNext()) {
      Tuple tuple = TupleUtils.toTuple(iter.next(), expressions);
      @SuppressWarnings("unchecked") // This type is mandated by the key type
      K[] row = (K[]) tuple.toArray();
      // end of workaround
      if (group == null) {
        group = new GroupImpl(groupExpressions, maps);
        groupId = row[0];
      } else if (!Objects.equals(groupId, row[0])) {
        list.add(transform(group));
        group = new GroupImpl(groupExpressions, maps);
        groupId = row[0];
      }
      group.add(row);
    }
    if (group != null) {
      list.add(transform(group));
    }
    iter.close();
    return list;
  }

  @SuppressWarnings("unchecked")
  protected V transform(Group group) {
    return (V) group;
  }
}