LINQ query not working properly for many-to-many relationship entities in EF core

[csnarain]

I have two entities in my database schema which has many-to-many relationship. I followed the EF core documentation (https://docs.microsoft.com/en-us/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-simple-key%2Csimple-key) by setting up a bridge table and mentioning the foreign key in DbContext appropriately. However, when I try to query my db using the LINQ query (see below), it's simply returning only the parent object and returning null for my child objects. I've setup a navigation property appropriately.

_context.Activities.Where(a => a.Id == id)
                .Include(a => a.Groups)
                .ThenInclude(b => b.GroupMembers)
                .ThenInclude(p => p.Members)
                .ToListAsync();

Also configured the composite keys using fluent api as shown below:

         modelBuilder.Entity<StudentCourse>().HasKey(p => new { p.StudentId, p.CourseId});

I tried to parse the underlying SQL query using SQL studio profiler which is executing the correct sql queries and the results are also returned accurately. It's only when the results are returned back, it's not getting displayed properly. My class structure is as given below. Group and Member are the entities that have many-to-many relationship and GroupMember is my bridge entity class. Is this an issue or am I doing something wrong here.

public class Activity
{
    public int Id { get; set; }
    public string ActivityName { get; set; }
    public DateTime ActivityDate { get; set; }
    
    [ForeignKey("Event")]
    public int EventId { get; set; }
    
   
    //navigation property
    public List<Group> Groups{ get; set; } = new List<Groups>();
}
public class Group
{
    public int Id { get; set; }
    [ForeignKey("Activity")]
    public int ActivityId { get; set; }
    
    public string GroupName { get; set; }
    
    //navigation property
    public List<GroupMember> GroupMembers { get; set; } = new List<GroupMember>();

}
public class GroupMember
{
    public int GroupId { get; set; }
    public int MemberId { get; set; }

    public Group Groups { get; set; } = new Group();
    public Member Members { get; set; } = new Member();
}

public class Member
{
    public int Id { get; set; }
    public string DisplayName { get; set; }
    public string Email { get; set; }
    
    [ForeignKey("Event")]
    public int EventId { get; set; }
    
    public bool IsDeleted { get; set; }
    
    //navigation property
    public List<GroupMember> GroupMembers { get; set; } = new List<GroupMember>();
}

[smitpatel]

Please share a runnable repro code which demonstrate issue you are seeing.

[csnarain]

I'm not allowed to share my source files. However, whatever I've provided above is very similar to what I'm using in my modules. All I'd like to know is if there is anything I'm missing wrt configuring m2m relationship in efcore

[ajcvickers]

@csnarain You cannot initialize reference navigation properties to empty objects. So this:

    public Group Groups { get; set; } = new Group();
    public Member Members { get; set; } = new Member();

Should be

    public Group Groups { get; set; }
    public Member Members { get; set; }

See #18007 for more info.