查询使用查询生成器从另一个表进行链接的表中的所有行

Question

我有一个只有几行变量的表。此行中的一行链接到另一个具有更多行的表。

要说清楚，1个表称为连接。变量是：

name, groupname, etc. 

groupname应链接到第二个名为ConnectionGroup的表。变量是：

name, id. 

我的想法是按名称查询到ConnectionGroup表。对于连接和ConnectionGroup抽象类是这样的：

public abstract class Connection_ { 

    public static volatile SingularAttribute<Connection, String>name; 
    public static volatile SingularAttribute<Connection, String>host; 
    public static volatile SetAttribute<Connection, ConnectionGroup>connectionGroups; 
} 

public abstract class ConnectionGroup_ { 

    public static volatile SingularAttribute<ConnectionGroup, String> name; 
    public static volatile SingularAttribute<ConnectionGroup, Long> id; 

} 

查询这个，我想我也来加入这两个表，然后只对它们进行查询。这是我曾尝试代码：

@PersistenceContext 
private EntityManager em; 

public List<Connection> retrieveAll(String groupFilter, int start, int length) { 
    ServiceUtil.requireAdmin(); 
    CriteriaBuilder cb = em.getCriteriaBuilder(); 
    CriteriaQuery<Connection> q = cb.createQuery(Connection.class); 
    Root<Connection> c = q.from(Connection.class); 
    Join<Connection, ConnectionGroup> join = c.join(Connection_.connectionGroups); 
    q.select(c); 

    c.fetch(Connection_.connectionGroups).fetch(ConnectionGroup_.id); 
    Predicate groupPredicate = cb.equal(
    c.get(Connection_.connectionGroups), "%" + groupFilter + "%"); 
    q.where(groupPredicate); 

    List<Connection> results = em.createQuery(q).setFirstResult(start) 
      .setMaxResults(length).getResultList(); 
    for (Connection conn : results) { 
     logger.info("getconnectionGroups =["+ conn.getConnectionGroups() + "]"); 
     for (ConnectionGroup conngroup : conn.getConnectionGroups()) { 
      logger.info("connectiongroups = [" + conngroup.getName() + "]"); 
     } 
    } 
} 

的事情，我都试过了，改变这个：

Predicate groupPredicate = cb.equal(
    c.get(Connection_.connectionGroups), "%" + groupFilter + "%"); 

这样：

Predicate groupPredicate = cb.equal(join.get(ConnectionGroup_.name), 
      "%" + groupFilter + "%"); 

更改此：

Join<Connection, ConnectionGroup> join = c 
      .join(Connection_.connectionGroups); 

对此：

Join<Connection, ConnectionGroup> join = c.join("connectionGroups"); 

当我尝试这些方法，我不断收到一个例外Cannot join to attribute of basic type

我也试图改变代码到这个：

CriteriaBuilder cb = em.getCriteriaBuilder(); 
CriteriaQuery<Connection> q = cb.createQuery(Connection.class); 
Root<Connection> c = q.from(Connection.class); 
Join<Connection, ConnectionGroup> join = (Join<Connection, ConnectionGroup>) c.fetch(Connection_.connectionGroups); 
q.select(c); 

Predicate groupPredicate = cb.equal(join.get(ConnectionGroup_.name), "%" + groupFilter + "%"); 
q.where(groupPredicate); 
List<Connection> results = em.createQuery(q).setFirstResult(start) 
      .setMaxResults(length).getResultList(); 

它会返回一个例外：

query specified join fetching, but the owner of the fetched association was not present in the select list

我使用这些网站作为参考编写鳕鱼E：

JPA CriteriaBuilder using fetch joins and result objects

JPA 2 Criteria Fetch Path Navigation

wiki.eclipse.org

developer.com

我如何可以查询从ConnectionGroup表的名字吗？我的方法错了吗？

Answer 1

如果您想通过字符串匹配使用名称过滤，CriteriaBuilder.like（）比CriteriaBuilder.equal（）更适合使用。

要实现您要查询的内容，您可以使用ff。JP QL查询：

SELECT DISTINCT conn FROM Connection conn JOIN conn.connectionGroups connGrp 
WHERE connGrp.name LIKE :groupFilter 

翻译JP QL到CriteriaQuery中，你必须：

CriteriaBuilder cb = em.getCriteriaBuilder(); 
CriteriaQuery<Connection> q = cb.createQuery(Connection.class); 
Root<Connection> conn = q.from(Connection.class); 
Join<Connection, ConnectionGroup> connGrp = conn.join(Connection_.connectionGroups); 
q.select(conn).distinct(true); 
ParameterExpression<String> param = cb.parameter(String.class, "%"+ groupFilter + "%"); 
q.where(cb.like(connGrp.get(ConnectionGroup_name), param));