Question

我正在使用EF 4.0，我需要使用一个内部联接和N个外部联接来实现查询我开始使用不同的方法实现这一点，但在某些时候陷入困境。

以下是我使用ObjectQuery<'T'> and Linq to Entity

开始执行此操作的两个示例

1）使用ObjectQuery<'T'>我实现了灵活的外连接，但我不知道在这种情况下如何使用实体规则执行内连接（默认情况下包括（“规则”）进行外连接，但我需要内部联接由Id）。

    public static IEnumerable<Race> GetRace(List<string> includes, DateTime date)
    {
        IRepository repository = new Repository(new BEntities());

        ObjectQuery<Race> result = (ObjectQuery<Race>)repository.AsQueryable<Race>();

        //perform outer joins with related entities
        if (includes != null)                   
            foreach (string include in includes)
                result = result.Include(include);


        //here i need inner join insteard of default outer join
        result = result.Include("Rules"); 

        return result.ToList();
    }

2）使用Linq To Entity我需要有一种外连接（在GetRace（）中有些东西，我可以传递一个包含实体的List）并且我还需要用实体规则执行正确的内连接

    public static IEnumerable<Race> GetRace2(List<string> includes, DateTime date)
    {
        IRepository repository = new Repository(new BEntities());

        IEnumerable<Race> result = from o in repository.AsQueryable<Race>()
                                   from b in o.RaceBetRules
                                   select new
                                   {
                                     o
                                   });

        //I need here:
        // 1. to perform the same way inner joins with related entities like with ObjectQuery above

        //here i getting List<AnonymousType> which i cant cast to 
        //IEnumerable<Race> when i did try to cast like 
        //(IEnumerable<Race>)result.ToList(); i did get error:
        //Unable to cast object of type 
        //'System.Collections.Generic.List`1[<>f__AnonymousType0`1[BetsTipster.Entity.Tip.Types.Race]]' 
        //to type 
        //'System.Collections.Generic.IEnumerable`1[BetsTipster.Entity.Tip.Types.Race]'.
        return result.ToList();
    }

可能有人对此有一些想法。

Answer 1

    public static IEnumerable<Race> GetRace(List<string> includes, DateTime date)
    {
        IRepository repository = new Repository(new BEntities());

        ObjectQuery<Race> result = (ObjectQuery<Race>)repository.AsQueryable<Race>();

        //perform outer joins with related entities
        if (includes != null)
            foreach (string include in includes)
                result = result.Include(include);


        //Perform inner join with "Rules" table
        result = (ObjectQuery<Race>)result.Include("Rules").Where(x => x.RaceBetRules.Any());

        result = (ObjectQuery<Race>)result.OrderBy(x => x.RaceDate);


        return result.ToList();
    }

Answer 2

这是一个post处理LINQ to Entities中的Inner Join。
希望这会为你指明正确的方向。

Entity Framework 4.0中的内部联接和外部联接选项

2 个答案: