java – Generic querydsl orderBy使用左连接生成动态路径

2019年7月21日 313次阅读

我在使用带有Querydsl和Hibernate的JPA进行数据存储管理时遇到了问题.样本模型如下：

@Entity
public class User {
    ....

    @ManyToOne
    @JoinColumn(name = "CATEGORY_ID")
    private Category category;
}

@Entity
public class Category {
    ..
    private String acronym;

    @OneToMany(mappedBy = "category")    
    List<User> userList;    
}

在我的Spring MVC webapp中,我有一个包含User parameters和orderBy select的搜索表单. orderBy select可以是User属性或Category属性. orderBy参数存储为Map(fe {“login”：“adm”,{“firstName”：“John”}.搜索功能接收搜索参数(作为字符串)和上面带有订单规范的地图.简化代码订购如下：

Map<String, String> orderByMap = new HashMap<String, String>();
orderByMap.put("firstName", "asc");
orderByMap.put("unit.acronym", "desc");

PathBuilder<User> pbu = new PathBuilder<User>(User.class, "user");

....

for (Map.Entry<String, String> order : orderByMap.entrySet())
{
    // for simplicity I've omitted asc/desc chooser
    query.orderBy(pbu.getString(order.getKey()).asc());
}

当我想按类别的参数引入排序时,问题就出现了,例如{“category.acronym”,“desc”}.正如here所解释的,上面的代码将使querydsl使用与Category表的交叉连接并且省略没有类别的用户,这不是预期的行为.

我知道,我必须使用Categories引入左连接并使用别名进行排序以使其正常工作,我正在寻找有效的方法来动态地完成它.剥离每个字符串寻找类别或任何其他实体(如“user.category.subcategory.propetry”)将引入许多丑陋的代码,我宁愿不这样做.

我会感谢一些更优雅的解决方案.

最佳答案 我现在在Querydsl
https://github.com/mysema/querydsl/issues/582的测试方面添加了一个原型实现

如果这是一个常见的用例,我会考虑直接集成到Querydsl

public class OrderHelper {

private static final Pattern DOT = Pattern.compile("\\.");

public static PathBuilder<?> join(JPACommonQuery<?> query, PathBuilder<?> builder, Map<String, PathBuilder<?>> joins, String path) {
    PathBuilder<?> rv = joins.get(path);
    if (rv == null) {
        if (path.contains(".")) {
            String[] tokens = DOT.split(path);
            String[] parent = new String[tokens.length - 1];
            System.arraycopy(tokens, 0, parent, 0, tokens.length - 1);
            String parentKey = StringUtils.join(parent, ".");
            builder = join(query, builder, joins, parentKey);
            rv = new PathBuilder(Object.class, StringUtils.join(tokens, "_"));
            query.leftJoin((EntityPath)builder.get(tokens[tokens.length - 1]), rv);
        } else {
            rv = new PathBuilder(Object.class, path);
            query.leftJoin((EntityPath)builder.get(path), rv);
        }
        joins.put(path, rv);
    }
    return rv;
}

public static void orderBy(JPACommonQuery<?> query, EntityPath<?> entity, List<String> order) {
    PathBuilder<?> builder = new PathBuilder(entity.getType(), entity.getMetadata());
    Map<String, PathBuilder<?>> joins = Maps.newHashMap();

    for (String entry : order) {
        String[] tokens = DOT.split(entry);
        if (tokens.length > 1) {
            String[] parent = new String[tokens.length - 1];
            System.arraycopy(tokens, 0, parent, 0, tokens.length - 1);
            PathBuilder<?> parentAlias = join(query, builder, joins, StringUtils.join(parent, "."));
            query.orderBy(parentAlias.getString(tokens[tokens.length - 1]).asc());
        } else {
            query.orderBy(builder.getString(tokens[0]).asc());
        }
    }
}

}
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