[英]Hibernate Criteria: counting the most recent entries, grouped per attribute
This is a knot I find quite hard to untie. 这是一个我很难解开的结。
My requirement is to use the Criteria
API. 我的要求是使用
Criteria
API。
I have a Team
class defined as follows: 我有一个
Team
类定义如下:
@Entity
@Table(name="TEAMS")
public class Team{
private Set<State> states = new HashSet<State>();
@OneToMany(cascade=CascadeType.ALL, orphanRemoval=true, mappedBy="team")
public Set<State> getStates() {
return states;
}
}
A Team
has a list of State
s because it transits through different states during its lifecycle. Team
有一个State
列表,因为它在其生命周期中通过不同的状态。 So the State
class is defined as follows. 所以
State
类定义如下。
@Entity
@Table(name="STATES")
public class State{
private Team team;
private StateType type;
private Date date;
@ManyToOne
@JoinColumn(name="TEAM_ID")
public Team getTeam() {
return team;
}
@Column(name="STATE_TYPE")
public StateType getType() {
return type;
}
@Temporal(TemporalType.DATE)
@Column(name="DATE")
public Date getDate() {
return date;
}
}
Now, what I want is to count the number of teams which are currently in a given state. 现在,我想要的是计算当前处于给定状态的团队数量。 The current state is the one with the most recent
date
value. 当前状态是具有最新
date
值的状态。
I tried with the following statement, but with no luck. 我尝试了以下声明,但没有运气。
public Long getStateTypeNumber(StateType type)
{
Session session = sessionFactory.getCurrentSession();
Criteria criteria = session.createCriteria(State.class);
criteria.add(Restrictions.eq("type", type));
criteria.addOrder(Order.desc("date"));
criteria.setProjection(Projections.distinct(Projections.property("team")));
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
criteria.setProjection(Projections.rowCount());
return (Long) criteria.uniqueResult();
}
can anyone provide some help? 谁能提供一些帮助? Thanks.
谢谢。
Well from what I see you're missing a join on your Team
. 好吧,从我看到你错过了你的
Team
加入。 But I would try it coming from Team
and joining your State
class. 但我会尝试从
Team
加入你的State
班级。
Session session = sessionFactory.getCurrentSession();
Criteria criteria = session.createCriteria(Team.class);
criteria.createAlias("states", state);
criteria.add(Restrictions.eq("state.type", type));
criteria.setProjection(Projections.rowCount());
(Long) criteria.uniqueResult();
Didn't test it because I don't have the enviroment with me, hope it works. 没有测试它,因为我没有环境,希望它有效。
I write in the following the solution I found for this problem. 我在下面写了我找到的解决这个问题的方法。 First, I have to retrieve a view of my
State
table containing the rows of the most recent states grouped by team, then I have to add restrictions for the type
. 首先,我必须检索包含按团队分组的最新状态行的
State
表的视图,然后我必须为该type
添加限制。 The trick here is to generate a subquery with a DetachedCriteria
to be used inside a Criteria
(thanks to @Jan for pointing it out). 这里的技巧是生成一个带有
DetachedCriteria
的子查询,以便在Criteria
(感谢@Jan指出它)。
public Long getStateTypeNumber(StateType type)
{
DetachedCriteria maxDateQuery = DetachedCriteria.forClass(State.class);
maxDateQuery.setProjection(Projections.projectionList().
add(Projections.max("date")).
add(Projections.groupProperty("team")));
Session session = sessionFactory.getCurrentSession();
Criteria criteria = session.createCriteria(State.class);
criteria.add(Subqueries.propertiesIn(new String[] {"date", "team"}, maxDateQuery));
criteria.add(Restrictions.eq("type", type));
criteria.setProjection(Projections.rowCount());
return (Long) criteria.uniqueResult();
}
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