[英]Hibernate criteria on collection values
I'm trying to put together a complicated query using Hibernate. 我正在尝试使用Hibernate组合一个复杂的查询。 I've been leaning toward Criteria, but I'm beginning to suspect it's not possible, and so any suggestions would be helpful.
我一直倾向于Criteria,但我开始怀疑它不可能,所以任何建议都会有所帮助。
I have an entity structure like the following: 我有一个如下的实体结构:
public class Attribute {
private Integer id;
private String name;
private Set<Value> values;
}
public class Instance {
private Integer id;
private int instanceRef;
private Set<Value> values;
}
public class Value {
private Integer id;
private Attribute attribute;
private String localAttributeName;
private Instance instance;
private String value;
}
These entities are related as you'd expect: 这些实体与您期望的相关:
value.attribute_id --> attribute.id
value.instance_id --> instance.id
Now, I would like to be able to take a set of attribute/value pairs (Strings) and find all instances that contain all of them. 现在,我希望能够获取一组属性/值对(字符串)并查找包含所有这些属性/值对的所有实例。 In Value, only one of attribute and localAttributeName are non-null, so the attribute name may match either localAttributeName or attribute.name.
在Value中,attribute和localAttributeName中只有一个是非null,因此属性名称可以匹配localAttributeName或attribute.name。 And to complicate things one last time, the unique index on Value is on (instance, attribute, value) or (instance, localAttributeName, value) -- that is, within an Instance, any given Attribute may have multiple Values.
最后一次使事情复杂化,Value上的唯一索引是(实例,属性,值)或(实例,localAttributeName,value) - 也就是说,在实例中,任何给定的Attribute都可能有多个值。
This is what I have so far: 这是我到目前为止:
public List<Instance> getMatchingInstances(Map<String, String> attrValues) {
Criteria crit = session.createCriteria(Instance.class, "i");
for(Map.Entry<String, String> entry : attrValues) {
DetachedCriteria valueCrit = DetachedCriteria.forClass(Value.class, "v");
// Do something here with valueCrit
crit.add(Subqueries.exists(valueCrit));
}
return crit.list();
}
Based on the research I've done, what I've tried for that Do something section is: 基于我已经完成的研究,我尝试过的是做某事的部分是:
// This would only check localAttributeName and not attribute.name.
// That's okay -- once I get the rest to work, I can figure this out.
valueCrit.add(Restrictions.eq("localAttributeName", entry.getKey());
valueCrit.add(Restrictions.eq("value", entry.getValue());
valueCrit.add(Restrictions.eqProperty("v.instance_id", "i.id"));
But this throws the exception below, which I suspect is telling me I can't do this with Criteria, but I'd love to learn otherwise: 但是这引发了下面的例外情况,我怀疑它是告诉我我不能用Criteria做到这一点,但是我很乐意学习:
java.lang.NullPointerException
at org.hibernate.loader.criteria.CriteriaQueryTranslator.getProjectedTypes(CriteriaQueryTranslator.java:341)
What would be the best way to go about doing this? 这样做最好的方法是什么?
I figured out the solution after a few hours of banging on it. 经过几个小时的撞击,我找到了解决方案。 Hopefully, this is of use to others.
希望这对其他人有用。 There were three main points that I needed to solve to make this feasible:
为了使这个可行,我需要解决三个要点:
I've highlighted each of these in the below code. 我在下面的代码中突出显示了这些内容。
First, to get rid of the exception, I discovered that the subquery needed a projection, highlighted below. 首先,为了摆脱异常,我发现子查询需要一个投影,下面突出显示。 I just did a projection on the "id" property of Instance.
我刚刚对Instance的“id”属性进行了投影。
Second, to get the join, I used the Criteria.createCriteria() methods to create a left outer join. 其次,为了获得连接,我使用了Criteria.createCriteria()方法来创建左外连接。 Because I had multiple conditions at different levels of the join, I had to save the joined Criteria and attach expressions to them separately.
因为我在连接的不同级别有多个条件,所以我必须保存连接的Criteria并将表达式分别附加到它们。 This let me do my OR expression in the subquery.
这让我在子查询中做我的OR表达式。
Finally, I had to add an eqProperty() clause to map the subquery back to the main Criteria. 最后,我必须添加一个eqProperty()子句来将子查询映射回主Criteria。 Just like it would need to be in the resulting SQL, I used: instance.id = i.id.
就像它需要在结果SQL中一样,我使用了:instance.id = i.id. Because I had already mapped the Instance Criteria to "i" and was adding this clause to the Value Criteria, this translated to the SQL: v.instance_id = i.id.
因为我已经将实例标准映射到“i”并且正在将此子句添加到Value Criteria,所以这转换为SQL:v.instance_id = i.id.
Here's the working code: 这是工作代码:
public List<Instance> getMatchingInstances(Map<String, String> attrValues) {
Criteria crit = session.createCriteria(Instance.class, "i");
for(Map.Entry<String, String> entry : attrValues) {
String attrName = entry.getKey();
String val = entry.getValue();
// Create the subquery
DetachedCriteria valueCrit = DetachedCriteria.forClass(Value.class, "v");
// Join the Attribute object (left outer join)
DetachedCriteria attrCrit =
valueCrit.createCriteria("attribute", CriteriaSpecification.LEFT_JOIN);
// Put together the OR statement on the Attribute joined criterion.
Criterion localAttr = Restrictions.eq("v.localAttributeName", attrName);
Criterion globalAttr = Restrictions.eq("name", attrName);
attrCrit.add(Restrictions.or(localAttr, globalAttr));
// Simple column equality on the subquery criterion.
valueCrit.add(Restrictions.eq("value", val));
// Map the subquery back to the outer query.
valueCrit.add(Restrictions.eqProperty("instance.id", "i.id"));
// Add the missing projection.
valueCrit.setProjection(Projections.property("id"));
// Add this subquery to the outer query.
crit.add(Subqueries.exists(valueCrit));
}
return crit.list();
}
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