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SQL support for Querydsl
There is a newer version: 5.1.0
/*
 * 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 java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javax.annotation.Nullable;

import com.google.common.collect.ImmutableList;
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;

/**
 * {@code WindowFirstLast} is a builder for window function expressions
 *
 * @author tiwe
 *
 * @param 
 */
public class WindowFirstLast extends MutableExpressionBase {

    private static final long serialVersionUID = 4107262569593794721L;

    private static final String ORDER_BY = "order by ";

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

    @Nullable
    private transient volatile SimpleExpression value;

    private final Expression target;

    private final boolean first;

    public WindowFirstLast(WindowOver target, boolean first) {
        super(target.getType());
        this.target = target;
        this.first = first;
    }

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

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

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

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

    public WindowFirstLast orderBy(OrderSpecifier... orderBy) {
        value = null;
        this.orderBy.addAll(Arrays.asList(orderBy));
        return this;
    }

    SimpleExpression getValue() {
        if (value == null) {
            if (orderBy.isEmpty()) {
                // TODO this check should be static
                throw new IllegalStateException("No order by arguments given");
            }
            ImmutableList.Builder> args = ImmutableList.builder();
            StringBuilder builder = new StringBuilder();
            builder.append("{0} keep (dense_rank ");
            args.add(target);
            builder.append(first ? "first " : "last ");
            builder.append(ORDER_BY);
            builder.append("{1}");
            args.add(ExpressionUtils.orderBy(orderBy));
            builder.append(")");
            value = Expressions.template(target.getType(), builder.toString(), args.build());
        }
        return value;
    }

    public WindowFunction over() {
        return new WindowFunction(getValue());
    }

}