如何在实体框架模型中的两个SQL视图上进行多联接？

Question

I have two views in my model.

I basically need to do an INNER JOIN on them based on three columns:

• dataSource
• ShowID
• EpisodeID

The first thing I don't know how to do is add the SQL "AND" operator to the LINQ expression.

The second thing is, I don't know how to SELECT the JOINED table.

Can someone give me a hand?

var query = (from s in db.TVData_VW_ShowList 
                         from z in db.TVData_VW_Schedule
                         where s.dataSource = z.dataSource
                         && s.ShowID = z.ShowID
                         && s.EpisodeId = z.EpisodeId select ...

Answer 1

You can use anonymous types to your advantage here, both to join across multiple columns, and to project into a new type containing data from both sides of the join. Here's a working example using Linq to objects:

namespace LinqExample
{
    class Program
    {
        static void Main()
        {
            var Shows = new List<ShowData> { new ShowData { dataSource = "foo", EpisodeID = "foo", ShowID = "foo", SomeShowProperty = "showFoo" }};
            var Schedules = new List<ScheduleData> { new ScheduleData { dataSource = "foo", EpisodeID = "foo", ShowID = "foo", SomeScheduleProperty = "scheduleFoo" } };

            var results =
                from show in Shows
                join schedule in Schedules
                    on new { show.dataSource, show.ShowID, show.EpisodeID }
                    equals new { schedule.dataSource, schedule.ShowID, schedule.EpisodeID }
                select new { show.SomeShowProperty, schedule.SomeScheduleProperty };

            foreach (var result in results)
            {
                Console.WriteLine(result.SomeShowProperty + result.SomeScheduleProperty); //prints "showFoo scheduleFoo"
            }

            Console.ReadKey();
        }
    }

    public class ShowData
    {
        public string dataSource { get; set; }
        public string ShowID { get; set; }
        public string EpisodeID { get; set; }
        public string SomeShowProperty { get; set; }
    }

    public class ScheduleData
    {
        public string dataSource { get; set; }
        public string ShowID { get; set; }
        public string EpisodeID { get; set; }
        public string SomeScheduleProperty { get; set; }
    }
}

Answer 2

So to join you can use the join keyword then use on to specify the conditions. && (the logical and operator in C#) will be translated to the SQL AND keyword.

Also, in EF they have what are known as "implicit joins" meaning if I have TableA with a foreign key to TableB, call it fKey.

Doing where TableA.fKey == TableB.pKey will cause the provider to put a join there. To select you simply need to do;

select new { prop1 = TableA.Prop1, prop2 = TableB.Prop1 }

this will create a new anonymous which selects values from both tables.

Below is a more complete example of the join syntax. I think it uses all of the things you asked about;

var result = from a in TableA
             join b in TableB on a.fKey equals b.pKey && b.Status equals 1
             select new { a.Prop1, a.Prop2, b.Prop1 };

Answer 3

First you need to create an auxiliar class that contains the columns of both views, something like:

public class viewItem 
{
   public int ShowID { get; set; }
   public int EpisodeID { get; set; }
   public int dataSource { get; set; }
   ...
}

then your linq query would be:

var query = (from s in db.TVData_VW_ShowList
             join z in db.TVData_VW_Schedule 
             on s.dataSource equals z.dataSource
             where s.ShowID == z.ShowID
             && s.EpisodeID == z.EpisodeID
             select new viewItem {
                ShowID = s.ShowID,
                EpisodeID = s.EpisodeID,
                dataSource = s.dataSource,
                ...
             }