ASP.NET Web API with Many-Many relationships - asp.net

Question

I'm having some trouble with ASP.NET Web API with many-many relationships between models. Here are my models (which I've simplified for brevity):
public class Model1
{
public int Model1ID { get; set; }
public string Name { get; set; }
public virtual ICollection<Model2> Model2s{ get; set; }
public string Self
{
get
{
return string.Format(CultureInfo.CurrentCulture,
"api/model1/{0}", this.Model1ID);
}
set { }
}
}
public class Model2
{
public int Model2ID { get; set; }
public string Name { get; set; }
public virtual ICollection<Model1> Model1s{ get; set; }
public string Self
{
get
{
return string.Format(CultureInfo.CurrentCulture,
"api/model2/{0}", this.Model2ID);
}
set { }
}
}
and my relevant Model1 API controller excerpt:
public class Model1sController : ApiController
{
private ApplicationDbContext db = new ApplicationDbContext();
// GET: api/Model1s
public IQueryable<Model1> GetModel1s()
{
return db.Model1s;
}
...
}
When I navigate to /api/model1s I get a long JSON nested error, here is the innermost Exception message.
There is already an open DataReader associated with this Command which must be closed first.
What I'm trying to achieve is output like this, but I cannot figure out how to get it working.
[{
"Model1ID": 1,
"Name": "Some model 2 name",
"Model2s": [{
"Model2ID": 1,
"Name": "Another model 2 name"
}, {
"Model2ID": 2,
"Name": "Some model 2 name"
}]
}, {
"Model1ID": 2,
"Name": "Another model 1 name",
"Model2s": [{
"Model2ID": 2,
"Name": "Some model 2 name"
}]
}]

Answer 1

What you need is called and associative entity, some devs call them a lookup table. An associative entity will hold the “association” between two other entities. In your case I believe that there is a scaffolding engine that will build the database tables for you based on the classes you create. Someone else may be able to speak to how the scaffolding engine works.
I would create a class called “TvProgramming” and give it properties Name, Id, Host_Id, Host_Name, and List. Now with this set up you can have as many hosts and as many tv shows as you want and still create unique programming schedules.
Adjust the tv show and host objects so that they only have properties that are unique to themselves ie a TvShow will have an name, id, and maybe a length. A host may have name, id, network, and location info however notice that the host object and tv show object have no knowledge of the other, only the associative entity holds knowledge of the relationship between them.
At the end of the day what your api should return is a set of TvProgramming objects that contain the hosts and for each host a list of tv shows… here is an quick example of the class structure I’m talking about, you’ll have to tweak it a bit to fit your needs but it should get started.
namespace YourProjectName.Models
{
public class TvShow
{
public int id { get; set; }
public string name { get; set; }
public TimeSpan length { get; set; }
public string rating { }
public TvShow() { }
}
public class Host
{
public int id { get; set; }
public string name { get; set; }
public string network { get; set; }
public string city { get; set; }
public string state { get; set; }
public string zip { get; set; }
public string country { get; set; }
public Host() { }
}
public class TvProgramming
{
public int id { get; set; }
public string name { get; set; }
public int host_Id { get; set; }
public string host_Name { get; set; }
public List<TvShow> shows { get; set; }
public TvProgramming()
{
this.shows = new List<TvShow>();
}
}
}

Answer 2

As a way of possibly preventing the error you are getting, try modifying your Controller code like this:
public class Model1sController : ApiController
{
// GET: api/Model1s
public IQueryable<Model1> GetModel1s()
{
using (var db = new ApplicationDbContext())
{
return db.Model1s;
}
}
}