[英]How do I do a custom projection with the Criteria API in NHibernate?
With HQL I can use dynamic instantiation like this: 使用HQL,我可以像这样使用动态实例化:
select new ItemRow(item.Id, item.Description, bid.Amount)
from Item item join item.Bids bid
where bid.Amount > 100
Now I need to create my queries dynamically with the Criteria API. 现在我需要使用Criteria API动态创建我的查询。 How can I obtain the same results that I would have obtained with HQL, but using the Criteria API?
我如何获得与使用HQL获得的结果相同的结果,但使用Criteria API?
Thank you. 谢谢。
You can use the AliasToBean result transformer. 您可以使用AliasToBean结果转换器。 ( Doc 1.2 ) It assigns every projection to a property of the same name.
( Doc 1.2 )它将每个投影分配给同名的财产。
session.CreateCriteria(typeof(Item), "item")
.CreateCriteria("Bids", "bid")
.SetProjection(Projections.ProjectionList()
.Add(Projections.Property("item.Id"), "Id" )
.Add(Projections.Property("item.Description"), "Description" )
.Add(Projections.Property("bid.Amount"), "Amount" ))
.Add(Expression.Gt("bid.Amount", 100))
.SetResultTransformer(Transformers.AliasToBean(typeof(ItemRow)))
.List();
Assuming you are using NHibernate 2.0.1 GA, here is the pertinent documentation: 假设您使用的是NHibernate 2.0.1 GA,以下是相关文档:
http://nhibernate.info/doc/nh/en/index.html#querycriteria-projection http://nhibernate.info/doc/nh/en/index.html#querycriteria-projection
Hope that helps! 希望有所帮助!
When you use a projection, the return type becomes Object or Object[] instead of the criteria type. 使用投影时,返回类型将变为Object或Object [],而不是条件类型。 You have to use a transformer.
你必须使用变压器。
Here is a simple ResultTransformer: 这是一个简单的ResultTransformer:
private class ProjectionTransformer implements ResultTransformer {
private String[] propertysList;
private Class<?> classObj;
/**
* @param propertysList
*/
public ProjectionTransformer(String[] propertysList) {
this.classObj = persistentClass;
this.propertysList = propertysList;
}
/**
* @param classObj
* @param propertysList
*/
public ProjectionTransformer(Class<?> classObj, String[] propertysList) {
this.classObj = classObj;
this.propertysList = propertysList;
}
@SuppressWarnings("unchecked")
public List transformList(List arg0) {
return arg0;
}
public Object transformTuple(Object[] resultValues, String[] arg1) {
Object retVal = null;
try {
retVal = Class.forName(classObj.getName()).newInstance();
int dot = -1;
for (int i = 0; i < resultValues.length; i++) {
if ((dot = propertysList[i].indexOf(".")) > 0) {
propertysList[i] = propertysList[i].substring(0, dot);
}
PropertyUtils.setProperty(retVal, propertysList[i], resultValues[i]);
}
} catch (Exception e) {// convert message into a runtimeException, don't need to catch
throw new RuntimeException(e);
}
return retVal;
}
}
Here's how you use it: 以下是您使用它的方式:
ProjectionList pl = (...)
String[] projection = new String[]{"Id","Description","Bid.Amount"};
crit.setProjection(pl).setResultTransformer(new ProjectionTransformer(projection));
I have not tested it for relations (eg: Bid.Amount). 我没有测试它的关系(例如:Bid.Amount)。
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