用LINQ连接联接表中的列

Question

I have 3 EF entities: Appeal , AppealPerson , Person .

Appeal and Person entities joined by AppealPerson entity (many-to-many relation). I want to select appeals with concatenated person full names.

+----------+----------+--------------------------------------------------+
| AppealId | Appeal.* | Person.Surname + Person.Name + Person.MiddleName |
+----------+----------+--------------------------------------------------+
| 1        | ..info.. | Aaa Aaa Aaa, Bbb Bbb Bbb, Ccc Ccc Ccc            |
+----------+----------+--------------------------------------------------+
| 2        | ..info.. | Aaa Aaa Aaa, Bbb Bbb Bbb                         |
+----------+----------+--------------------------------------------------+

Now I'm using this query:

context.Appeals
.Select(a => new
{
  Appeal = a,
  Persons = a.AppealPersons
    .Select(ap => ap.Person)
    .Select(p => new { p.Surname, p.Name, p.MiddleName })
    .ToList()
})
.AsEnumerable()
.Select(a => new
{
  Id = a.Appeal.Id,
  Persons = a.Persons.Select(p => string.Format("{0} {1} {2}", p.Surname, p.Name, p.MiddleName).Trim()),
})
.ToList<object>();

This query is very slow. List for ~500 rows generated in 30 seconds. Please help to optimize query.

Answer 1

Try with joins such as:

from a in context.Appeals
join ap in context.AppealPerson
on a.Id equals ap.AppealId
join p in context.Person
on p.Id equals ap.PersonId
...

Answer 2

Looking at your relationships, I think you can do this with a GroupBy clause. Given the formatting has to happen client-side it would be a bit less cluttered if you either had a function which wrapped up this or, even better, override ToString on Person

public partial class Person
{
    ...
    public string override ToString()
    {
        return String.Format("{0} {1} {2}", Surname, Name, MiddleName).Trim();
    }
}
...
context.AppealPersons
    .GroupBy(ap => ap.Appeal.Id, ap => ap,
        (key, g) => new { 
            AppealId = key, 
            Appeal = g.FirstOrDefault().Appeal, 
            Persons = String.Join(",", g.Select(x => x.Person).AsEnumerable()
                .Select(p => p.ToString()))
        })
    .ToList();