Question

我有很多关系：

帖子可以包含多个标签
标签可以有很多帖子

型号：

public class Post
{
    public virtual string Title { get; set; }
    public virtual string Content{ get; set; }
    public virtual User User { get; set; }
    public virtual ICollection<Tag> Tags { get; set; }
}

public class Tag
{
    public virtual string Title { get; set; }
    public virtual string Description { get; set; }
    public virtual User User { get; set; }
    public virtual ICollection<Post> Posts { get; set; }
}

我想计算属于多个标签的所有帖子，但我不知道如何在NHibernate中执行此操作。我不确定这是否是最好的方法，但我在MS SQL中使用了这个查询：

SELECT COUNT(*) 
    FROM 
    (
    SELECT Posts.Id FROM Posts
    INNER JOIN Users ON Posts.UserId=Users.Id 
    LEFT JOIN TagsPosts ON Posts.Id=TagsPosts.PostId 
    LEFT JOIN Tags ON TagsPosts.TagId=Tags.Id 
    WHERE Users.Username='mr.nuub' AND (Tags.Title in ('c#', 'asp.net-mvc')) 
    GROUP BY Posts.Id 
    HAVING COUNT(Posts.Id)=2
    )t

但是NHibernate不允许from子句中的子查询。如果有人能告诉我如何在HQL中执行此操作，那将会很棒。

Answer 1

我找到了一种如何在没有子查询的情况下获得此结果的方法，这适用于nHibernate Linq。实际上并不那么容易，因为nqibernate支持linq表达式的子集...但是无论如何

查询：

var searchTags = new[] { "C#", "C++" };
var result = session.Query<Post>()
        .Select(p => new { 
            Id = p.Id, 
            Count = p.Tags.Where(t => searchTags.Contains(t.Title)).Count() 
        })
        .Where(s => s.Count >= 2)
        .Count();

它产生以下sql语句：

select cast(count(*) as INT) as col_0_0_ 
from Posts post0_ 
where (
    select cast(count(*) as INT)
    from PostsToTags tags1_, Tags tag2_ 
    where post0_.Id=tags1_.Post_id 
    and tags1_.Tag_id=tag2_.Id 
    and (tag2_.Title='C#' or tag2_.Title='C++'))>=2

我希望你能够在此构建用户限制。

以下是我的测试设置和生成的随机数据

public class Post
{
    public Post()
    {
        Tags = new List<Tag>();
    }
    public virtual void AddTag(Tag tag)
    {
        this.Tags.Add(tag);
        tag.Posts.Add(this);
    }
    public virtual string Title { get; set; }
    public virtual string Content { get; set; }
    public virtual ICollection<Tag> Tags { get; set; }
    public virtual int Id { get; set; }
}

public class PostMap : ClassMap<Post>
{
    public PostMap()
    {
        Table("Posts");

        Id(p => p.Id).GeneratedBy.Native();

        Map(p => p.Content);

        Map(p => p.Title);

        HasManyToMany<Tag>(map => map.Tags).Cascade.All();
    }
}

public class Tag
{
    public Tag()
    {
        Posts = new List<Post>();
    }
    public virtual string Title { get; set; }
    public virtual string Description { get; set; }
    public virtual ICollection<Post> Posts { get; set; }
    public virtual int Id { get; set; }
}

public class TagMap : ClassMap<Tag>
{
    public TagMap()
    {
        Table("Tags");
        Id(p => p.Id).GeneratedBy.Native();

        Map(p => p.Description);
        Map(p => p.Title);
        HasManyToMany<Post>(map => map.Posts).LazyLoad().Inverse();
    }
}

试运行：

var sessionFactory = Fluently.Configure()
    .Database(FluentNHibernate.Cfg.Db.MsSqlConfiguration.MsSql2012
        .ConnectionString(@"Server=.\SQLExpress;Database=TestDB;Trusted_Connection=True;")
        .ShowSql)
    .Mappings(m => m.FluentMappings
        .AddFromAssemblyOf<PostMap>())
    .ExposeConfiguration(cfg => new SchemaUpdate(cfg).Execute(false, true))
    .BuildSessionFactory();

using (var session = sessionFactory.OpenSession())
{
    var t1 = new Tag() { Title = "C#", Description = "C#" };
    session.Save(t1);
    var t2 = new Tag() { Title = "C++", Description = "C/C++" };
    session.Save(t2);
    var t3 = new Tag() { Title = ".Net", Description = "Net" };
    session.Save(t3);
    var t4 = new Tag() { Title = "Java", Description = "Java" };
    session.Save(t4);
    var t5 = new Tag() { Title = "lol", Description = "lol" };
    session.Save(t5);
    var t6 = new Tag() { Title = "rofl", Description = "rofl" };
    session.Save(t6);
    var tags = session.Query<Tag>().ToList();
    var r = new Random();

    for (int i = 0; i < 1000; i++)
    {
        var post = new Post()
        {
            Title = "Title" + i,
            Content = "Something awesome" + i,
        };

        var manyTags = r.Next(1, 3);

        while (post.Tags.Count() < manyTags)
        {
            var index = r.Next(0, 6);
            if (!post.Tags.Contains(tags[index]))
            {
                post.AddTag(tags[index]);
            }
        }

        session.Save(post);
    }
    session.Flush();

    /* query test */
    var searchTags = new[] { "C#", "C++" };
    var result = session.Query<Post>()
            .Select(p => new { 
                Id = p.Id, 
                Count = p.Tags.Where(t => searchTags.Contains(t.Title)).Count() 
            })
            .Where(s => s.Count >= 2)
            .Count();

    var resultOriginal = session.CreateQuery(@"
       SELECT COUNT(*) 
        FROM 
        (
        SELECT count(Posts.Id)P FROM Posts
        LEFT JOIN PostsToTags ON Posts.Id=PostsToTags.Post_id 
        LEFT JOIN Tags ON PostsToTags.Tag_id=Tags.Id 
        WHERE Tags.Title in ('c#', 'C++')
        GROUP BY Posts.Id 
        HAVING COUNT(Posts.Id)>=2
        )t
    ").List()[0];

    var isEqual = result == (int)resultOriginal;
}

正如您在最后看到的那样，我会根据您的原始查询进行测试（没有用户），它实际上是相同的数量。

Answer 2

编辑：将来我应该阅读问题，直到最后的话。我会看到in HQL ...

经过一番搜索，意识到RowCount删除了查询中的任何分组（https://stackoverflow.com/a/8034921/1236044）。我找到了使用QueryOver和SubQuery的解决方案，我在此处将其作为信息发布。我发现这个解决方案很有意思，因为它提供了一些模块化，并从子查询本身分离计数，可以按原样重复使用。

var searchTags = new[] { "tag1", "tag3" };
var userNames = new[] { "mr.nuub" };
Tag tagAlias = null;
Post postAlias = null;
User userAlias = null;

var postsSubquery =
    QueryOver.Of<Post>(() => postAlias)
            .JoinAlias(() => postAlias.Tags, () => tagAlias)
            .JoinAlias(() => postAlias.User, () => userAlias)
            .WhereRestrictionOn(() => tagAlias.Title).IsIn(searchTags)
            .AndRestrictionOn(() => userAlias.UserName).IsIn(userNames)
            .Where(Restrictions.Gt(Projections.Count<Post>(p => tagAlias.Title), 1));

var numberOfPosts = session.QueryOver<Post>()
            .WithSubquery.WhereProperty(p => p.Id).In(postsSubquery.Select(Projections.Group<Post>(p => p.Id)))
            .RowCount();

希望这会有所帮助

Answer 3

在HQL中：

var hql = "select count(p) from Post p where p in " +
    "(select t.Post from Tag t group by t.Post having count(t.Post) > 1)";
var result = session.Query(hql).UniqueResult<long>();

如果需要指定标记或其他条件，可以向子查询添加其他条件。

如何计算NHibernate中属于多个标签的所有帖子？

3 个答案: