One-to-Many relations in RESTful api using Web Api 2 - json

Question

I have a question about setting up Web Api 2 so that if there is a relationship between two entities, at least querying one of those includes the other entities in the result. It's hard to explain but very easy concept if you look at the example below:
So, Imagine here is what we have in the Entity Framework:
public class student {
public int Id {get; set;}
public string Name {get; set;}
public int School_Id {get;set;}
public virtual School School {get; set;}
}
And:
public class school {
public int Id {get; set;}
public string Name {get; set;}
public IEnumerable<Student> Students {get; set;}
}
So obviously this is a very simple example. It's clear that these two classes can cause a circular reference, is there an easy way for me to generate json output that from one side, includes the related property and from the other side it doesn't? (to prevent the circular reference), to make it clear, when I query schools, I want to get this:
[{Id:1, Name: "School A", Students: [{Id:1, Name:"Mike"}, {Id:2, Name: "Sheila"}]} ,
{Id:2, Name: "School B", Students: [{Id:3, Name:"Joe"}, {Id:4, Name: "Sarah"}]}]
And when I query students, I only get this (see there is no school):
[{Id:1, Name:"Mike", School_Id:1}, {Id:2, Name:"Sheila", School_Id:1}, {Id:3, Name:"Joe", School_Id:2}, {Id:4, Name:"Sarah", School_Id:2}]

Answer 1

There are a few ways to handle this situation, and the method you choose depends on a few factors. I'll list the common ways this is normally dealt with, and you can evaluate each to decide which makes sense for both your client and server configuration.
Use a View Model or anonymous projection. This method involves creating a unique class which has only the properties you wish to send to the client.
public class StudentVm {
public int Id {get; set;}
public string Name {get; set;}
public string SchoolName {get;set;}
}
Use the [JsonIgnore] attribute on properties you do not want to have JSON serialize. If you prefer the Opt-In approach, use [DataMember] on properties you wish to include in serialization.
public class student {
public int Id {get; set;}
public string Name {get; set;}
public int School_Id {get;set;}
[JsonIgnore]
public virtual School School {get; set;} //omitted
}
public class student {
[DataMember]
public int Id {get; set;}
[DataMember]
public string Name {get; set;}
[DataMember]
public int School_Id {get;set;}
public virtual School School {get; set;} //omitted by default
}
Use the initializer for the JSON Formatter to preserve references. A unique $id field will be added to each object, and any object which may cause a circular reference will be replaced with a $ref pointing to that object's $id value.
var json = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling =
Newtonsoft.Json.PreserveReferencesHandling.All;
[{"$id":"1", "Id":"1", "Name":"Mike", "School_Id":"1",
{"$id":"2", "Id":"1", "Name": "School A", "Students": [{"$ref":"1"}]
}]
Note that using a combination of these methods together is acceptable; You could, for example, use a View Model and use References Handling together.
References from http://www.asp.net/web-api/overview/formats-and-model-binding/json-and-xml-serialization

Answer 2

Could you explicitly create objects in the form you want?
Schools.Select(s => new
{
s.Id,
s.Name,
Students = s.Students.Select(st => new {st.Id, st.Name})
})
Students.Select(st => new { st.Id, st.Name, st.School_Id })