Linq To Entities中的左外部联接（不能在LINQ to Entities查询中构造实体或复杂类型。）

Question

I have two class that map two tables of my database:

public class Product
{
    public int Id { get; set; }
    public string Token { get; set; }
    public string Name { get; set; }
    public decimal Value { get; set; }
}

public class Ticket
{
    public int Id { get; set; }
    public string SerialNumber { get; set; }
    public string ProductToken { get; set; }
    public Product Product { get; set; }
}

For some domain reasons, Product and Ticket are logically linked, in other words, they are not linked in a database relationship that could be mapped by EF, they will be linked in my app with a linq query that "must" be translated in a SQL Outer Left Join. From this, i did the following query:

IQueryble<Ticket> query = from ts in context.Tickets
                          join ps in context.Products 
                               on ts.ProductToken equals ps.Token into p
                          select new Ticket
                          {
                              Id = t.Id,  
                              SerialNumber = t.SerialNumber,
                              ProductToken = t.ProductToken,
                  Goal -----> Product = p.FirstOrDefault()
                          };

The query keeps as IQueryble because after that, the query keeps to be refined with a filter.

The problem is when i run the following code:

var tickets = query.OrderBy(t => t.SerialNumber).ToList();

I got the following error:

"The entity or complex type 'Model.Ticket' cannot be constructed in a LINQ to Entities query."

So, how can i reach my goal?

Answer 1

You cannot project the result to a mapped entity, either you could project it to a annonymous type or create your own Ticket type something like:

public class myTicket
{
    public int Id { get; set; }
    public string SerialNumber { get; set; }
    public string ProductToken { get; set; }
    public Product Product { get; set; }
}

and then:

IQueryble<myTicket> query = from ts in context.Tickets
                          join ps in context.Products 
                               on t.ProductToken equals p.Token into p
                          select new myTicket
                          {
                              Id = t.Id,  
                              SerialNumber = t.SerialNumber,
                              ProductToken = t.ProductToken,
                              Product = p.FirstOrDefault()
                          };

Also you need to use DefaultIfEmpty() for left outer join