How can I select a column within a dictionary value with nhibernate?

问题

I have structure similar to this:

public class Entity
{
    public int Id { get; set; }
    public IDictionary<string, EntityLocale> Locales { get; set; }
}
public class EntityLocale
{
    public string Name { get; set; }
}
public class EntityMap : ClassMap<Entity>
{
    public EntityMap()
    {
        HasMany(x => x.Locales)
                .AsMap<string>("Locale")
                .Component(
                c => {
                         c.Map(x => x.Name);
                     }
                );
    }
}

And I want to recieve all names of product locales with a "en" key. With linq it will be:

var names = Session.QueryOver<Product>().List().Select(x => x.Locales["en"].Name).ToList();

How do I achieve this with nhibernate? (I don't care if it's QueryOver or Criteria api, I just don't want to select everything).

Update

I came up with the following ugly hack (which I'm not satisfied with, I don't want any sql in my code):

var names = Session.CreateSQLQuery("SELECT Name FROM ProductLocales WHERE Locale = 'en'").List<string>()

回答1:

For these cases, NHibernate has very nice solution: 18.1. NHibernate filters. At the end, we will select Product and apply filter on the dictionary... therefore having only SingleOrDefault() item in the Locales.

Definiton of the Filter

public class CulturFilter : FilterDefinition
{
  public CulturFilter()
  {
    WithName("CulturFilter")
        .AddParameter("culture",NHibernate.NHibernateUtil.String);
  }
}

and apply it

HasMany(x => x.Locales)
  .AsMap<string>("Locale")
  ... 
  .ApplyFilter<CulturFilter>("Locale = :culture"))
;

From that moment, whenever you enable the filter in the session (even with some AOP filter), you can be sure that the IDictionary contains exactly one (or none) element..

session.EnableFilter("CultureFilter")
    .SetParameter("culture", "en");

// applied every time
var criteria = session.CreateCritieria...
var query = session.QueryOver....

There is similar posts with some more links if needed https://stackoverflow.com/a/17109300/1679310

EDIT: Restricting the column "Locale" directly, getting the list of Names

Other approach (keeping the current solution almost the same) which could be used (and I know about) is to extend the LocalEntity mapping

public class EntityLocale
{
    public virtual string CultureName { get; set; }
    public virtual string Name { get; set; }
}
public class EntityMap : ClassMap<Entity>
{
    public EntityMap()
    {
        HasMany(x => x.Locales)
            .AsMap<string>("Locale")
            .Component(
            c => {
                c.Map(x => x.CultureName).Formula("Locale").Not.Insert().Not.Update();
                c.Map(x => x.Name);
            }
        );
    }
}

Having this, we can get the list of all "en" Names like this:

var criteria = 
    session.QueryOver<Entity>()
    .JoinQueryOver<IDictionary<string, EntityLocale>>(c => c.Locales)
    .UnderlyingCriteria;

var list = criteria
    .Add(Restrictions.Eq("CultureName", "en"))
    .SetProjection(Projections.SqlProjection("Name"
        , new string[] { "name" }
        , new IType[] { NHibernateUtil.String }))
    .List()
    .Cast<string>()
    .ToList<String>();

Now we have a list containing all the Names from EntityLocale filtered by "en" culture

来源：https://stackoverflow.com/questions/17240037/how-can-i-select-a-column-within-a-dictionary-value-with-nhibernate

标签

nhibernate

queryover

nhibernate-criteria