Fetching complex objects by raw SQL query in Entity Framework

问题

I would like to fetch from database complex object using single query. Let's look at the following example:

SELECT TableA.*, TableB.*
FROM TableA
INNER JOIN TableA.B_Id = TableB.Id

and corresponding classes:

public class QueryResult
{
    public TableA A { get; set; }
    public TableB B { get; set; }
}

public class TableA
{
    public int Id { get; set; }
    public string SomeContentA { get; set; }
    public int B_Id { get; set; }
}

public class TableB
{
    public int Id { get; set; }
    public int SomeContentB { get; set; }
}

I would like to execute the raw SQL query from above against the database and get collection of QueryResult objects with correctly set A and B properties. So far I tried using SqlQuery method, but I only managed to get collection of QueryResult objects with nulls in A and B properties (apparently returned result set was not correctly binded to properties):

var results = ctx.Database.SqlQuery<QueryResult>(\\example_query).ToList();

Note that:

I shouldn't list manually columns in SELECT statement. TableA and TableB classes and SQL tables are likely to change over time, but those changes will be consistent.
Three queries (one to fetch IDs from TableA and TableB, second to fetch objects from TableA, third for objects from TableB) will hurt performance and I should try avoid it if possible.

I am using Entity Framework 4.3 and SQL Server 2012.

Thanks, Art

回答1:

You can still use regular EF constructions by just mapping your classes to their corresponding tables and forcing the join in LINQ-To-Entities:

using(var ctx = new MyDbContext())
{
    return ctx.TableA
         .Join(ctx.TableB, a=>a.B_Id, b=>b.Id, (a,b)=>
              new QueryResult{TableA=a, TableB=b});
}

I think that's the only way, at least up to EF6.

来源：https://stackoverflow.com/questions/31180826/fetching-complex-objects-by-raw-sql-query-in-entity-framework

标签

sql-server-2012

entity-framework-4.3