EF Code first - Detect one-to-many relationships property for given type

Question

We know that we do not need to configure for one-to-many relationships using Data Annotations, one-to-many relationship configured by convention.

In following example ICollection<Student> Students is an relationship property

public class Student
{
    public Student() { }

    public int StudentId { get; set; }
    public string StudentName { get; set; }

    public virtual Standard Standard { get; set; }
}

public class Standard
{
    public Standard()
    {
        Students = new List<Student>();
    }
    public int StandardId { get; set; }
    public string Description { get; set; }

    public virtual ICollection<Student> Students { get; set; }
}

So my question is, how can I detect a relationship propertys for a given type? My goal is to test the value of the property and how many items it contains

Something like that:

static void Test(object givenInstanse)
{
    foreach (PropertyInfo p in TryGetOneToManyRelationshipsPropertys(typeof(givenInstanse), dc))
    {
        var val = (ICollection)p.GetValue(givenInstanse);
        Console.WriteLine(val.Count);
    }
}

static IEnumerable<PropertyInfo> TryGetOneToManyRelationshipsPropertys(Type t, DbContext dc)
{
    // ...
}

Answer 1

In its simplest form (Not taking into considerations any custom attributes or custom Mappings). You can do this:

IEnumerable<PropertyInfo> GetOneToManyRelationships<T>()
{
    var collectionProps = from p in typeof(T).GetProperties()
                          where p.PropertyType.IsGenericType
                                && p.PropertyType.GetGenericTypeDefinition() 
                                                   == typeof(ICollection<>)
                          select p;

    foreach (var prop in collectionProps)
    {
        var type = prop.PropertyType.GetGenericArguments().First(); 

        // This checks if the other type has a One Property of this Type.
        bool HasOneProperty = type.GetProperties().Any(x => x.PropertyType == typeof(T));

        if(!HasOneProperty)
        {
            string pkName = typeof(T).Name + "Id";

            HasOneProperty = type.GetProperties().Any(x => x.Name.Equals(pkName, 
                                                      StringComparison.OrdinalIgnoreCase));
        }

        if (HasOneProperty)
        {
            yield return prop;
        }
    }
}

Usage:

var oneToManyProps = GetOneToManyRelationships<Standard>();

foreach(var prop in oneToManyProps)
{
    Console.WriteLine(prop.Name);
}

Output:

Students

You can extend this to check for Attributes tagged on properties, but i'll leave that to you as it is outside the scope of your question.