blocks|key|3072051|text|如果我正确理解了您的配置，这实际上是预期的行为。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3072052|在任何结果中都会得到相同的Order实例，但是由于现在您正在使用OrderTransaction进行连接，因此它必须返回与常规sql连接相同数量的结果|offset|length|style|CODE|3072053|所以实际上它应该出现多次。作者(Gavin+King)本人here很好地解释了这一点:它既解释了原因，也解释了如何仍然获得明显的结果|3072054|​|3072055|3072056|在Hibernate+FAQ中也提到：|3072057|3072058|对于为集合启用了外部连接获取的查询，|3072059|+Hibernate不会返回distinct结果(即使我使用了distinct关键字)？首先，您需要了解SQL以及外连接在SQL中是如何工作的。如果您不能完全理解和理解SQL中的外部连接，请不要继续阅读本常见问题解答，而应参考SQL手册或教程。否则，您将无法理解下面的解释，并且您将在Hibernate论坛上抱怨此行为。|blockquote|BOLD|3072060|3072061|可能返回相同Order对象的重复引用的典型示例：|3072062|List+result+=+session.createCriteria(Order.class)+.setFetchMode("lineItems"，FetchMode.JOIN)+.list()；|3072063|3072064|3072065|..。|3072066|3072067|List+result+=+session.createCriteria(Order.class)+.list()；List+result+=+session.createQuery("select+o+from+Order+O+left+join+fetch+o.lineItems").list()；|3072068|所有这些示例都会生成相同的SQL语句：|3072069|SELECT+o.*，l.*+from+ORDER+O+LEFT+OUTER+JOIN+LINE_ITEMS+l+ON+o.ID+=+l.ORDER_ID|3072070|想知道为什么会有重复的东西吗？查看SQL结果集，Hibernate不会在外部连接结果的左侧隐藏这些重复项，而是返回驱动表的所有重复项。如果数据库中有5个订单，并且每个订单有3个行项目，则结果集将为15行。这些查询的Java结果列表将有15个元素，它们的类型都是Order。Hibernate只会创建5个Order实例，但SQL结果集的副本将保留为对这5个实例的重复引用。如果您不理解这最后一句话，您需要阅读Java以及Java堆上的实例和对此类实例的引用之间的区别。|3072071|(为什么是左外部连接？如果您有一个没有行项目的额外订单，结果集将是16行，右侧填充为空，其中行项目数据用于其他订单。即使他们没有行项目，你也想要订单，对吧？如果没有，请在HQL中使用内部连接获取)。|3072072|默认情况下，Hibernate不会过滤掉这些重复的引用。有些人(而不是你)实际上想要这样。你怎么过滤掉它们呢？|3072073|如下所示：|3072074|采集结果=新的LinkedHashSet(+session.create*(...).list()+)；|3072075|entityMap|0|LINK|mutability|MUTABLE|url|http://community.jboss.org/wiki/HibernateFAQ-AdvancedProblems#Hibernate_does_not_return_distinct_results_for_a_query_with_outer_join_fetching_enabled_for_a_collection_even_if_I_use_the_distinct_keyword|1^0|0|D|5|W|G|0|T|4|0|0|0|0|B|3|1|0|0|0|1|4F|0|0|0|O|0|0|2S|0|0|0|0|3|0|0|0|48|0|0|J|0|0|25|0|0|6H|0|0|2R|0|0|1J|0|0|5|0|0|1G|0^^$0|@$1|2|3|4|5|6|7|1U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1V|8|@$D|1W|E|1X|F|G]|$D|1Y|E|1Z|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|20|8|@]|9|@$D|21|E|22|1|23]]|A|$]]|$1|J|3|K|5|6|7|24|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|25|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|26|8|@]|9|@$D|27|E|28|1|29]]|A|$]]|$1|O|3|K|5|6|7|2A|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|2B|8|@]|9|@]|A|$]]|$1|R|3|S|5|T|7|2C|8|@$D|2D|E|2E|F|U]]|9|@]|A|$]]|$1|V|3|-4|5|6|7|2F|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|2G|8|@$D|2H|E|2I|F|U]]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|2J|8|@$D|2K|E|2L|F|U]]|9|@]|A|$]]|$1|10|3|-4|5|6|7|2M|8|@]|9|@]|A|$]]|$1|11|3|-4|5|6|7|2N|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|2O|8|@$D|2P|E|2Q|F|U]]|9|@]|A|$]]|$1|14|3|-4|5|6|7|2R|8|@]|9|@]|A|$]]|$1|15|3|16|5|6|7|2S|8|@$D|2T|E|2U|F|U]]|9|@]|A|$]]|$1|17|3|18|5|6|7|2V|8|@$D|2W|E|2X|F|U]]|9|@]|A|$]]|$1|19|3|1A|5|6|7|2Y|8|@$D|2Z|E|30|F|U]]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|31|8|@$D|32|E|33|F|U]]|9|@]|A|$]]|$1|1D|3|1E|5|6|7|34|8|@$D|35|E|36|F|U]]|9|@]|A|$]]|$1|1F|3|1G|5|6|7|37|8|@$D|38|E|39|F|U]]|9|@]|A|$]]|$1|1H|3|1I|5|6|7|3A|8|@$D|3B|E|3C|F|U]]|9|@]|A|$]]|$1|1J|3|1K|5|6|7|3D|8|@$D|3E|E|3F|F|U]]|9|@]|A|$]]|$1|1L|3|-4|5|6|7|3G|8|@]|9|@]|A|$]]]|1M|$1N|$5|1O|1P|1Q|A|$1R|1S]]|1T|$5|1O|1P|1Q|A|$1R|1S]]]]

This is actually the expected behaviour if I understood your configuration correctly.

You get the same <code>Order</code> instance in any of the results, but since now you are doing a join with the <code>OrderTransaction</code>, it has to return the same amount of results a regular sql join will return

So actually it should apear multiple times. this is explained very well by the author (Gavin King) himself <a href="http://community.jboss.org/wiki/HibernateFAQ-AdvancedProblems#Hibernate_does_not_return_distinct_results_for_a_query_with_outer_join_fetching_enabled_for_a_collection_even_if_I_use_the_distinct_keyword" rel="noreferrer">here</a>: 
It both explains why, and how to still get distinct results

<hr>
Also mentioned in the Hibernate <a href="http://community.jboss.org/wiki/HibernateFAQ-AdvancedProblems#Hibernate_does_not_return_distinct_results_for_a_query_with_outer_join_fetching_enabled_for_a_collection_even_if_I_use_the_distinct_keyword" rel="noreferrer">FAQ</a> :

<blockquote>
 Hibernate does not return distinct results for a query with outer join fetching enabled for a collection (even if I use the distinct
 keyword)? First, you need to understand SQL and how OUTER JOINs work
 in SQL. If you do not fully understand and comprehend outer joins in
 SQL, do not continue reading this FAQ item but consult a SQL manual or
 tutorial. Otherwise you will not understand the following explanation
 and you will complain about this behavior on the Hibernate forum.
 
 Typical examples that might return duplicate references of the same
 Order object:

<pre><code>List result = session.createCriteria(Order.class)
 .setFetchMode("lineItems", FetchMode.JOIN)
 .list();
</code></pre>
 
 <hr>

<pre><code>&lt;class name="Order"&gt;
 ...
 &lt;set name="lineItems" fetch="join"&gt;
</code></pre>
 
 <hr>

<pre><code>List result = session.createCriteria(Order.class)
 .list();
List result = session.createQuery("select o from Order o left join fetch o.lineItems").list();
</code></pre>
 
 All of these examples produce the same SQL statement:

<pre><code>SELECT o.*, l.* from ORDER o LEFT OUTER JOIN LINE_ITEMS l ON o.ID = l.ORDER_ID
</code></pre>
 
 Want to know why the duplicates are there? Look at the SQL resultset,
 Hibernate does not hide these duplicates on the left side of the outer
 joined result but returns all the duplicates of the driving table. If
 you have 5 orders in the database, and each order has 3 line items,
 the resultset will be 15 rows. The Java result list of these queries
 will have 15 elements, all of type Order. Only 5 Order instances will
 be created by Hibernate, but duplicates of the SQL resultset are
 preserved as duplicate references to these 5 instances. If you do not
 understand this last sentence, you need to read up on Java and the
 difference between an instance on the Java heap and a reference to
 such an instance.
 
 (Why a left outer join? If you'd have an additional order with no line
 items, the result set would be 16 rows with NULL filling up the right
 side, where the line item data is for other order. You want orders
 even if they don't have line items, right? If not, use an inner join
 fetch in your HQL).
 
 Hibernate does not filter out these duplicate references by default.
 Some people (not you) actually want this. How can you filter them out?
 
 Like this:

<pre><code>Collection result = new LinkedHashSet( session.create*(...).list() );
</code></pre>
</blockquote>

blocks|key|3285545|text|除了Eran提到的之外，另一种获得你想要的行为的方法是设置结果转换器：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3285546|criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);|code-block|syntax|javascript|3285547|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In addition to what is mentioned by Eran, another way to get the behavior you want, is to set the result transformer:

<pre><code>criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
</code></pre>

blocks|key|322435|text|试一试|type|unstyled|depth|inlineStyleRanges|entityRanges|data|322436|@Fetch+(FetchMode.SELECT)+|code-block|syntax|javascript|322437|例如|322438|@OneToMany(targetEntity+=+OrderTransaction.class,+fetch+=+FetchType.EAGER,+cascade+=+CascadeType.ALL)
@Fetch+(FetchMode.SELECT)
public+List<OrderTransaction>+getOrderTransactions()+{
return+orderTransactions;|322439|}|322440|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

try

<pre><code>@Fetch (FetchMode.SELECT) 
</code></pre>

for example

<pre><code>@OneToMany(targetEntity = OrderTransaction.class, fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@Fetch (FetchMode.SELECT)
public List&lt;OrderTransaction&gt; getOrderTransactions() {
return orderTransactions;
</code></pre>

}

blocks|key|319905|text|不要使用List和ArrayList，而要使用Set和HashSet。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|319906|@OneToMany(targetEntity+=+OrderTransaction.class,+cascade+=+CascadeType.ALL)
public+Set<OrderTransaction>+getOrderTransactions()+{
++++return+orderTransactions;
}|code-block|syntax|javascript|319907|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Do not use List and ArrayList but Set and HashSet.

<pre><code>@OneToMany(targetEntity = OrderTransaction.class, cascade = CascadeType.ALL)
public Set&lt;OrderTransaction&gt; getOrderTransactions() {
 return orderTransactions;
}
</code></pre>

blocks|key|3285666|text|使用Java+8和我在实用程序方法中添加的Streams，该return语句如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3285667|return+results.stream().distinct().collect(Collectors.toList());|code-block|syntax|javascript|3285668|数据流删除重复项的速度非常快。我在实体类中使用注释，如下所示：|3285669|@OneToMany(cascade+=+CascadeType.ALL,+fetch+=+FetchType.EAGER)
@JoinTable(name+=+"STUDENT_COURSES")
private+List<Course>+courses;|3285670|我想在我的应用程序中使用会话的方法是我需要数据库中的数据。完成后关闭会话。当然，将我的实体类设置为使用leasy+fetch类型。我去重构。|3285671|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Using Java 8 and Streams I add in my utility method this return statment:

<pre><code>return results.stream().distinct().collect(Collectors.toList());
</code></pre>

Streams remove duplicate very fast. I use annotation in my Entity class like this:

<pre><code>@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
@JoinTable(name = "STUDENT_COURSES")
private List&lt;Course&gt; courses;
</code></pre>

I think is bether in my app to use session in method where I need data from data base. Closse session when I done. Ofcourse set my Entity class to use leasy fetch type. I go to refactor.

blocks|key|319945|text|我在获取2个关联的集合时也遇到了同样的问题:用户有2个角色(Set)和2个套餐(List)，并且套餐是重复的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|319946|@Table(name+=+"users")
public+class+User+extends+AbstractNamedEntity+{

+++@CollectionTable(name+=+"user_roles",+joinColumns+=+@JoinColumn(name+=+"user_id"))
+++@Column(name+=+"role")
+++@ElementCollection(fetch+=+FetchType.EAGER)
+++@BatchSize(size+=+200)
+++private+Set<Role>+roles;

+++@OneToMany(fetch+=+FetchType.LAZY,+mappedBy+=+"user")
+++@OrderBy("dateTime+DESC")
+++protected+List<Meal>+meals;
+++...
}|code-block|syntax|javascript|319947|DISTINCT没有帮助(DATA-JPA查询)：|319948|@EntityGraph(attributePaths={"meals",+"roles"})
@QueryHints({@QueryHint(name=+org.hibernate.jpa.QueryHints.HINT_PASS_DISTINCT_THROUGH,+value+=+"false")})+//+remove+unnecessary+distinct+from+select
@Query("SELECT+DISTINCT+u+FROM+User+u+WHERE+u.id=?1")
User+getWithMeals(int+id);|319949|最后我找到了两个解决方案：|319950|319951|Change+List+to+LinkedHashSet|ordered-list-item|offset|length|319952|Use+EntityGraph只有一个字段"meal“和类型LOAD，它按照角色声明的方式加载角色(EAGER和by+BatchSize=200以防止N%2B1问题)：|319953|319954|最终解决方案：|319955|@EntityGraph(attributePaths+=+{"meals"},+type+=+EntityGraph.EntityGraphType.LOAD)
@Query("SELECT+u+FROM+User+u+WHERE+u.id=?1")
User+getWithMeals(int+id);|319956|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.jboss.org/wiki/HibernateFAQ-AdvancedProblems#jive_content_id_Hibernate_does_not_return_distinct_results_for_a_query_with_outer_join_fetching_enabled_for_a_collection_even_if_I_use_the_distinct_keyword^0|0|0|0|0|0|0|0|S|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|19|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1B|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|1D|8|@]|9|@$Q|1E|R|1F|1|1G]]|A|$]]|$1|S|3|T|5|P|7|1H|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|1J|8|@]|9|@]|A|$]]|$1|X|3|Y|5|D|7|1K|8|@]|9|@]|A|$E|F]]|$1|Z|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]]|10|$11|$5|12|13|14|A|$15|16]]]]

I have the same problem to fetch 2 associated collections: user has 2 roles (Set) and 2 meals (List) and meals are duplicated.

<pre><code>@Table(name = "users")
public class User extends AbstractNamedEntity {

 @CollectionTable(name = "user_roles", joinColumns = @JoinColumn(name = "user_id"))
 @Column(name = "role")
 @ElementCollection(fetch = FetchType.EAGER)
 @BatchSize(size = 200)
 private Set&lt;Role&gt; roles;

 @OneToMany(fetch = FetchType.LAZY, mappedBy = "user")
 @OrderBy("dateTime DESC")
 protected List&lt;Meal&gt; meals;
 ...
}
</code></pre>

DISTINCT doesn't help (DATA-JPA query):

<pre><code>@EntityGraph(attributePaths={"meals", "roles"})
@QueryHints({@QueryHint(name= org.hibernate.jpa.QueryHints.HINT_PASS_DISTINCT_THROUGH, value = "false")}) // remove unnecessary distinct from select
@Query("SELECT DISTINCT u FROM User u WHERE u.id=?1")
User getWithMeals(int id);
</code></pre>

At last I've found 2 solutions:

<ol>
<li><a href="https://developer.jboss.org/wiki/HibernateFAQ-AdvancedProblems#jive_content_id_Hibernate_does_not_return_distinct_results_for_a_query_with_outer_join_fetching_enabled_for_a_collection_even_if_I_use_the_distinct_keyword" rel="nofollow noreferrer">Change List to LinkedHashSet</a></li>
<li>Use EntityGraph with only field "meal" and type LOAD, which load roles as they declared (EAGER and by BatchSize=200 to prevent N+1 problem):</li>
</ol>

Final solution:

<pre><code>@EntityGraph(attributePaths = {"meals"}, type = EntityGraph.EntityGraphType.LOAD)
@Query("SELECT u FROM User u WHERE u.id=?1")
User getWithMeals(int id);
</code></pre>

blocks|key|319958|text|应用外部连接并带来重复的结果听起来并不是一个很好的行为。剩下的唯一解决方案是使用streams过滤我们的结果。感谢java8提供了更简单的过滤方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|319959|return+results.stream().distinct().collect(Collectors.toList());|code-block|syntax|javascript|319960|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

It doesn't sounds a great behavior applying an outer join and bring duplicated results. The only solution left is to filter our result using streams. Thanks java8 giving easier way to filter.

<pre><code>return results.stream().distinct().collect(Collectors.toList());
</code></pre>

blocks|key|3072252|text|而不是使用像这样的黑客：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3072253|用|3072254|Set代替List|unordered-list-item|offset|length|style|CODE|3072255|criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);|3072256|3072257|不修改您的sql查询，我们可以使用(引用JPA规范)|3072258|q.select(emp).distinct(true);|code-block|syntax|javascript|3072259|它确实修改了所得到的sql查询，因此其中具有DISTINCT。|3072260|entityMap^0|0|0|0|3|5|4|0|0|1P|0|0|0|0|M|8|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@$G|11|H|12|I|J]|$G|13|H|14|I|J]]|9|@]|A|$]]|$1|K|3|L|5|F|7|15|8|@$G|16|H|17|I|J]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|18|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|19|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|1A|8|@]|9|@]|A|$S|T]]|$1|U|3|V|5|6|7|1B|8|@$G|1C|H|1D|I|J]]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|X|$]]

Instead of using hacks like :

<ul>
<li><code>Set</code> instead of <code>List</code></li>
<li><code>criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);</code></li>
</ul>

which don't modify your sql query , we can use (quoting JPA specs)

<pre><code>q.select(emp).distinct(true);
</code></pre>

which does modify the resulting sql query,thus having a <code>DISTINCT</code> in it.

I have an <code>Order</code> class that has a list of <code>OrderTransactions</code> and I mapped it with a one-to-many Hibernate mapping like so:

<pre><code>@OneToMany(targetEntity = OrderTransaction.class, cascade = CascadeType.ALL)
public List&lt;OrderTransaction&gt; getOrderTransactions() {
 return orderTransactions;
}
</code></pre>

These <code>Order</code>s also have a field <code>orderStatus</code>, which is used for filtering with the following Criteria: 

<pre><code>public List&lt;Order&gt; getOrderForProduct(OrderFilter orderFilter) {
 Criteria criteria = getHibernateSession()
 .createCriteria(Order.class)
 .add(Restrictions.in("orderStatus", orderFilter.getStatusesToShow()));
 return criteria.list();
}
</code></pre>

This works and the result is as expected.

Now here is my question: Why, when I set the fetch type explicitly to <code>EAGER</code>, do the <code>Order</code>s appear multiple times in the resulting list?

<pre><code>@OneToMany(targetEntity = OrderTransaction.class, fetch = FetchType.EAGER, cascade = CascadeType.ALL)
public List&lt;OrderTransaction&gt; getOrderTransactions() {
 return orderTransactions;
}
</code></pre>

How would I have to change my Criteria code to reach the same result with the new setting?

Hibernate Criteria returns children multiple times with FetchType.EAGER

我有一个包含OrderTransactions列表的Order类，并将其映射为一个一对多的Hibernate映射，如下所示：@OneToMany(targetEntity = OrderTransaction.class, cascade = CascadeType.ALL)public List<OrderTrans...

问Hibernate Criteria使用FetchType.EAGER多次返回子对象
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