LINQ to Entities instead of stored procedure?

问题

I am using the Entity Framework to access my database and I just figured out that mapping stored procedures to methods using entity is a bit too complex and probably not well suited to do what I want exacltly. I am new to LINQ and I am wondering if I sould be better off just with ADO.NET. Here is the SQL code I need to translate:

SELECT p.Player_id, p.Name, p.Position, SUM(s.Goals) AS goalsb, SUM(s.Assists) AS assistsb, SUM(s.Points) AS pointsb
FROM Dim_Player AS p INNER JOIN Fact_Statistics AS s ON s.Player_id = p.Player_id
GROUP BY p.Player_id, p.Name, p.Position
ORDER BY pointsb DESC, goalsb DESC

With the Entities mapping for stored procedures, I had this code written:

HockeyStatsEntities db = new HockeyStatsEntities();

public ActionResult Index()
{
    ViewBag.Message = "League leaders";
    {
        return View(db.ListLeagueLeaders());
    }
}

public ActionResult About()
{
    return View();
}

private ICollection<ListLeagueLeaders_Result> ListLeagueLeaders()
{
    ICollection<ListLeagueLeaders_Result> leagueLeadersCollection = null;

    using (HockeyStatsEntities context = new HockeyStatsEntities())
    {
        foreach (ListLeagueLeaders_Result leagueLeader in
                  context.ListLeagueLeaders())
        {
            leagueLeadersCollection.Add(leagueLeader);
        }
    }
    return leagueLeadersCollection;
}

Here is the error I am getting:

The model item passed into the dictionary is of type 'System.Data.Objects.ObjectResult`1[NHLStats2.Models.ListLeagueLeaders_Result]', but this dictionary requires a model item of type 'NHLStats2.Models.ListLeagueLeaders_Result'.

But I realize that this is a bit of a pain in the ?&*@... How could I re-arrange this using a different, more effective method? Thanks for your help, it's really appreciated.

回答1:

You can write a simple LINQ query, using a model with these 2 tables, keeping their relationship:

from p in ctx.Dim_Player
select new {p.Player_id, p.Name, Goals = p.Fact_Statstics.Select(x=>(int?)x.Goals).Sum()}

You Dim_Player will have a FactStatistics property with the related statistics. You can apply subqueries with the SUMs and COUNTs you want.

The query above is returning an anonymous type, but you can create a class with the desired properties.

It's important to use the (int?) cast.

回答2:

Finally opting for using a stored procedure, this compiles and works:

Model1.tt.Context.cs (autogenerated)

public DbSet<Dim_Date> Dim_Date { get; set; }
    public DbSet<Dim_Player> Dim_Player { get; set; }
    public DbSet<Dim_Team> Dim_Team { get; set; }
    public DbSet<Fact_Statistics> Fact_Statistics { get; set; }
    public DbSet<Dim_Game> Dim_Game { get; set; }

    public virtual ObjectResult<ListLeagueLeaders_Result> ListLeagueLeaders()
    {
        ((IObjectContextAdapter)this).ObjectContext.MetadataWorkspace.LoadFromAssembly(typeof(ListLeagueLeaders_Result).Assembly);

        return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<ListLeagueLeaders_Result>("ListLeagueLeaders");
    }

View

@model System.Data.Objects.ObjectResult<NHLStats2.Models.ListLeagueLeaders_Result>

@{
    ViewBag.Title = "Index";
}

[...]

Problem was with the strongly typed view type not matching the System.Data.Objects.ObjectResult type. Was: @model NHLStats2.Models.ListLeagueLeaders_Result, changed to: @model System.Data.Objects.ObjectResult<NHLStats2.Models.ListLeagueLeaders_Result> Cheers!

来源：https://stackoverflow.com/questions/8543261/linq-to-entities-instead-of-stored-procedure