Nullable object must have a value in join tables query

Question

I have three tables TableTeam, TableUser and TableLink. I want to join them to get a list.

var teams = _db.TableTeam;
var users = _db.TableUser;
var managerIds = teams.Select(x=>x.ManagerId).ToList();
var list = (from user in _db.TableUser
        where user.EndDate == null && user.ManagerId != null && managerIds.Contains(user.ManagerId.Value)
        let r = _db.TableLink.FirstOrDefault(l => l.ProjectId == projectId && l.UserId  == user.UserId)
        let t = _db.TableTeam.FirstOrDefault(m => m.ManagerId == user.ManagerId)
        select new MyDto
        {
            ProjectId = projectId,
            UserId = user.UserId,
            IsAssigned = r.AssignedId > 0 ?true : false,
            AssignedId = r.AssignedId,
            Percent = r.Percent.HasValue ? (r.Percent.Value).ToString() + "%": ""
        }).GroupBy(d => d.UserId).ToList();

For the table TableLink, the corresponding dataSet class in entity framework is:

public LinkDto
{
   public int AssignedId {get;set;}
   public short ProjectId {get;set;}
   public short UserId {get;set;}
   public decimal? Percent {get;set;}
   // ...
}   

However I got the error:

Nullable object must have a value

I think that it may be caused by decimal? Percent. But not sure how to fix it. Also I can use the store d procedure as well, which means if you can solve it by SQL query, that is also great.

Answer 1

It turns out I have to move let codes before where clause then add the condition to where.

Such as

var list = (from user in _db.TableUser
    let r = _db.TableLink.FirstOrDefault(l => l.ProjectId == projectId && l.UserId  == user.UserId)
    let t = _db.TableTeam.FirstOrDefault(m => m.ManagerId == user.ManagerId)
    where user.EndDate == null && user.ManagerId != null && managerIds.Contains(user.ManagerId.Value) 
    && r != null && t != null
    select new MyDto
    {
        ProjectId = projectId,
        UserId = user.UserId,
        IsAssigned = r.AssignedId > 0 ?true : false,
        AssignedId = r.AssignedId,
        Percent = r.Percent.HasValue ? (r.Percent.Value).ToString() + "%": ""
    }).GroupBy(d => d.UserId).ToList();