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SQL support for Querydsl
There is a newer version: 6.9
/*
 * Copyright 2015, 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.sql;

import com.querydsl.core.types.*;
import com.querydsl.core.types.dsl.ComparableExpressionBase;
import com.querydsl.core.types.dsl.Expressions;
import com.querydsl.core.types.dsl.SimpleExpression;
import com.querydsl.core.types.dsl.SimpleOperation;
import com.querydsl.core.util.CollectionUtils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.jetbrains.annotations.Nullable;

/**
 * {@code WithinGroup} is a builder for {@code WITHIN GROUP} constructs
 *
 * @param  expression type
 * @author tiwe
 */
public class WithinGroup extends SimpleOperation {

  private static final long serialVersionUID = 464583892898579544L;

  private static Expression merge(Expression... args) {
    if (args.length == 1) {
      return args[0];
    } else {
      return ExpressionUtils.list(Object.class, args);
    }
  }

  /** Intermediate step */
  public class OrderBy extends MutableExpressionBase {

    private static final long serialVersionUID = -4936481493030913621L;

    private static final String ORDER_BY = "order by ";

    @Nullable private transient volatile SimpleExpression value;

    private final List> orderBy = new ArrayList>();

    public OrderBy() {
      super(WithinGroup.this.getType());
    }

    @SuppressWarnings("unchecked")
    public SimpleExpression getValue() {
      if (value == null) {
        int size = 0;
        List> args = new ArrayList<>();
        StringBuilder builder = new StringBuilder();
        builder.append("{0} within group (");
        args.add(WithinGroup.this);
        size++;
        if (!orderBy.isEmpty()) {
          builder.append(ORDER_BY);
          builder.append("{").append(size).append("}");
          args.add(ExpressionUtils.orderBy(orderBy));
        }
        builder.append(")");
        value =
            Expressions.template(
                (Class) WithinGroup.this.getType(),
                builder.toString(),
                CollectionUtils.unmodifiableList(args));
      }
      return value;
    }

    @Override
    public  R accept(Visitor v, C context) {
      return getValue().accept(v, context);
    }

    public OrderBy orderBy(ComparableExpressionBase orderBy) {
      value = null;
      this.orderBy.add(orderBy.asc());
      return this;
    }

    public OrderBy orderBy(ComparableExpressionBase... orderBy) {
      value = null;
      for (ComparableExpressionBase e : orderBy) {
        this.orderBy.add(e.asc());
      }
      return this;
    }

    public OrderBy orderBy(OrderSpecifier orderBy) {
      value = null;
      this.orderBy.add(orderBy);
      return this;
    }

    public OrderBy orderBy(OrderSpecifier... orderBy) {
      value = null;
      Collections.addAll(this.orderBy, orderBy);
      return this;
    }
  }

  public WithinGroup(Class type, Operator op) {
    super(type, op, Collections.emptyList());
  }

  public WithinGroup(Class type, Operator op, Expression arg) {
    super(type, op, Collections.singletonList(arg));
  }

  public WithinGroup(Class type, Operator op, Expression arg1, Expression arg2) {
    super(type, op, Arrays.asList(arg1, arg2));
  }

  public WithinGroup(Class type, Operator op, Expression... args) {
    super(type, op, merge(args));
  }

  public OrderBy withinGroup() {
    return new OrderBy();
  }
}