NHibernate 3.2 QueryOver按属性区分 [英] NHibernate 3.2 QueryOver distinct by property

问题描述

我有两节课

public class News
{
    public virtual int Id { get; protected set; }
    public virtual string Topic { get; set; }
    public virtual Category Category { get; set; }
}

public class Category
{
     public virtual int Id { get; protected set; }
     public virtual string Name { get; set; }
     public virtual ISet<News> News { get; set; }
}

和映射

 <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="News" namespace="NewsManagement.Models">
     <class name="News" table="News">
        <id name="Id">
             <generator class="native" />
         </id>
         <property name="Date" not-null="true" />
         <many-to-one name="Category" fetch="join" column="CategoryId" class="Category, NHibernateManyToOne" not-null="true"/>
     </class>
 </hibernate-mapping>

 <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="News" namespace="NewsManagement.Models">
     <class name="Category" table="Categories">
         <id name="Id" column="Id">
             <generator class="native" />
         </id>
         <set name="News" fetch="join" cascade="all-delete-orphan">
             <key column="CategoryId" />
             <one-to-many class="News, NHibernateOneToMany" /> 
         </set>
     </class>
 </hibernate-mapping>

我想获取分页新闻，按其类别名称排序. 这是查询:

And i want to take paged news, sorted by its category's name. Here is the query:

Session.QueryOver<News>().JoinQueryOver(x => x.Category).OrderBy(x => x.Name).Asc.Skip(pageNumber*pageSize).Take(pageSize).List<News>();

但是结果，我在列表中选择了许多重复的新闻.我认为这可能是因为在映射中启用了联接并且在查询中使用了联接.那么，有什么解决方案可以通过一个属性或另一种方法来区分来避免此问题吗?

But in result i take many duplicated news in my list. I think it's probably because of joins both enabled in mappings and used in query. So, is there any solution how to do distinct by one property or another way to avoid this problem?

推荐答案

您可以实现自己的IEqualityComparer并将其添加到查询中.

You can implement your own IEqualityComparer and add it to your query like this.

class MyEqualityComparer : IEqualityComparer<News>
{
    public bool Equals(News x, News y)
    {
        return x.Id == y.Id;
    }

    public int GetHashCode(News obj)
    {
        return obj.Id.GetHashCode();
    }
}

然后像这样使用它

 Session.QueryOver<News>().JoinQueryOver(x => x.Category).List<News>()
            .Distinct(new MyEqualityComparer())
            .OrderBy(x => x.Category.Name).Skip(pageNumber * pageSize).Take(pageSize).ToList();

考虑修复您的联接，这样就不会在将.Left添加到联接中时得到重复.

Consider fixing your join so you don't get duplicates adding .Left to your join.

Session.QueryOver<News>().Left.JoinQueryOver(x => x.Category)

如文档中所述.

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