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JPA 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.jpa;

import java.util.List;

import javax.persistence.Entity;

import com.google.common.collect.Lists;
import com.querydsl.core.support.ConstantHidingExpression;
import com.querydsl.core.support.EnumConversion;
import com.querydsl.core.support.NumberConversion;
import com.querydsl.core.support.NumberConversions;
import com.querydsl.core.types.*;
import com.querydsl.core.types.dsl.Expressions;
import com.querydsl.sql.RelationalPath;
import com.querydsl.sql.SQLOps;

/**
 * {@code Conversions} provides module specific projection conversion functionality
 *
 * @author tiwe
 *
 */
public final class Conversions {

    public static  Expression convert(Expression expr) {
        if (expr instanceof FactoryExpression) {
            FactoryExpression factoryExpr = (FactoryExpression) expr;
            for (Expression e: factoryExpr.getArgs()) {
                if (needsConstantRemoval(e)) {
                    return convert(new ConstantHidingExpression(factoryExpr));
                }
            }
            for (Expression e : factoryExpr.getArgs()) {
                if (needsNumberConversion(e)) {
                    return new NumberConversions(factoryExpr);
                }
            }
        } else if (needsNumberConversion(expr)) {
            return new NumberConversion(expr);
        }
        return expr;
    }

    private static boolean needsConstantRemoval(Expression expr) {
        expr = ExpressionUtils.extract(expr);
        return expr instanceof Constant || expr.equals(Expressions.TRUE) || expr.equals(Expressions.FALSE) ||
              (expr instanceof Operation && ((Operation) expr).getOperator() == Ops.ALIAS
                  && needsConstantRemoval(((Operation) expr).getArg(0)));
    }

    private static boolean needsNumberConversion(Expression expr) {
        expr = ExpressionUtils.extract(expr);
        return Number.class.isAssignableFrom(expr.getType()) && !Path.class.isInstance(expr);
    }

    private static boolean isEntityPathAndNeedsWrapping(Expression expr) {
        if ((expr instanceof Path && expr.getType().isAnnotationPresent(Entity.class)) ||
            (expr instanceof EntityPath && !RelationalPath.class.isInstance(expr))) {
            Path path = (Path) expr;
            if (path.getMetadata().getParent() == null) {
                return true;
            }
        }
        return false;
    }

    private static  FactoryExpression createEntityPathConversions(FactoryExpression factoryExpr) {
        List> conversions = Lists.newArrayList();
        for (Expression e : factoryExpr.getArgs()) {
            if (isEntityPathAndNeedsWrapping(e)) {
                conversions.add(ExpressionUtils.operation(e.getType(), SQLOps.ALL, e));
            } else {
                conversions.add(e);
            }
        }
        return FactoryExpressionUtils.wrap(factoryExpr, conversions);
    }

    public static  Expression convertForNativeQuery(Expression expr) {
        if (isEntityPathAndNeedsWrapping(expr)) {
            return ExpressionUtils.operation(expr.getType(), SQLOps.ALL, expr);
        } else if (Number.class.isAssignableFrom(expr.getType())) {
            return new NumberConversion(expr);
        } else if (Enum.class.isAssignableFrom(expr.getType())) {
            return new EnumConversion(expr);
        } else if (expr instanceof FactoryExpression) {
            FactoryExpression factoryExpr = (FactoryExpression) expr;
            boolean numberConversions = false;
            boolean hasEntityPath = false;
            for (Expression e : factoryExpr.getArgs()) {
                if (isEntityPathAndNeedsWrapping(e)) {
                    hasEntityPath = true;
                } else if (Number.class.isAssignableFrom(e.getType())) {
                    numberConversions = true;
                } else if (Enum.class.isAssignableFrom(e.getType())) {
                    numberConversions = true;
                }
            }
            if (hasEntityPath) {
                factoryExpr = createEntityPathConversions(factoryExpr);
            }
            if (numberConversions) {
                factoryExpr = new NumberConversions(factoryExpr);
            }
            return factoryExpr;
        }
        return expr;
    }

    private Conversions() { }

}