Hello,
I have a many to many relation with these models:
public class Bookmark{
public virtual string Title { get; set; }
public virtual string Link { get; set; }
public virtual User User { get; set; }
public virtual ICollection<Tag> Tags { get; set; }
public Bookmark()
{
Tags = new List<Tag>();
}}
public class Tag{
public virtual string Title { get; set; }
public virtual string Description { get; set; }
public virtual User User { get; set; }
public virtual ICollection<Bookmark> Bookmarks { get; set; }
public Tag()
{
Bookmarks = new List<Bookmark>();
}}
I need to load a specific tag for example: c# for user: Mr.nuub
In my view I use the tag title and description followed by all bookmarks
that this tag contains. For each bookmark I also need all tags that belongs
to it.
I used the following criteria:
public Tag GetTagByTitle(string username, string title){
ICriteria criteriaQuery = SessionFactory.GetCurrentSession()
.CreateCriteria(typeof(Tag))
.SetFetchMode("Bookmarks", FetchMode.Eager)
.CreateAlias("User", "User")
.Add(Restrictions.Eq("Title", title))
.Add(Restrictions.Eq("User.Username", username));
IList<Tag> tags = criteriaQuery.List<Tag>();
Tag tag = tags.FirstOrDefault();
return tag;}
This results in a join that returns a tag with its bookmarks. However for
each bookmark NHibernate creates a new query to obtain its tags. I want one
single query so I changed my criteria to this:
public Tag GetTagByTitle(string username, string title){
ICriteria criteriaQuery = SessionFactory.GetCurrentSession()
.CreateCriteria(typeof(Tag))
.SetFetchMode("Bookmarks", FetchMode.Eager)
.SetFetchMode("Bookmarks.Tags", FetchMode.Eager)
.CreateAlias("User", "User")
.Add(Restrictions.Eq("Title", title))
.Add(Restrictions.Eq("User.Username", username))
.SetResultTransformer(Transformers.DistinctRootEntity);
IList<Tag> tags = criteriaQuery.List<Tag>();
Tag tag = tags.FirstOrDefault();
return tag;}
I mapped the many to many as a set so this works fine. However NHibernate
Profiler tells me that I used too many joins and this might be a
performance problem. When is this becoming a performance problem and is
there a better way to do this? Is perhaps HQL better suited for this?
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