无法使用实体框架中的相关数据填充ICollection

Question

I have tables with created using below models in Entity Framework

public class User
{
    public int Id{ get; set; }
    public string Name { get; set; }       
    public bool IsActive { get; set; }
    public ICollection<AssigneeMonth> AssigneeMonths { get; set; }
}

public class AssigneeMonth
{
    public int Id { get; set; }
    public int AssigneeId { get; set; }
    public Month Month { get; set; }
    public User Assignee { get; set; }
}

public class ProjectAssignee
{
    public int Id { get; set; }
    public int ProjectId { get; set; }
    public int AssigneeId { get; set; }

    public bool IsActive { get; set; }
    public AutomationProject Project { get; set; }

    [ForeignKey("AssigneeId")]
    public User User { get; set; }
}

I am trying to get data into the collection AssigneeMonths from AssigneeMonth using this code:

 var assn = dataContext.ProjectAssignees
                       .Where(r => r.Project.Name == project.Name && r.IsActive)
                       .Include(u => u.User)
                       .ToList();

But AssigneeMonths collection in the above assn is always null even if I have data in AssigneeMonth for the user

May I know what's wrong with the above code?

Answer 1

Since you're using eager loading, you're only loading the information for user, not its navigational properties.

You can use the code in this answer , which applied to your case will look like this:

var assn = dataContext.ProjectAssignees
                   .Where(r => r.Project.Name == project.Name && r.IsActive)
                   .Include(u => u.User.SelectMany(u => u.AssigneeMonths))
                   .ToList();

Since AssigneeMonths is a collection, you need to use SelectMany instead of Select.

Other option would be to do it like this (as posted in other answers in that link):

var assn = dataContext.ProjectAssignees
                   .Where(r => r.Project.Name == project.Name && r.IsActive)
                   .Include(u => u.User)
                   .Include("User.AssigneeMonths")
                   .ToList();

But I personally don't like the second method because its easy to make mistakes with the string and it will hide the errors until runtime.