可为空的对象必须在连接表查询中具有值

Question

我有三个 table TableTeam、TableUser 和 TableLink。我想加入他们得到一个列表。

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();

对于tableTableLink，entity framework中对应的dataSetclass是：

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

但是我得到了错误：

Nullable object must have a value

我认为可能是decimal? Percent造成的。但不确定如何修复它。我也可以使用 store d 过程，这意味着如果你可以通过 SQL 查询解决它，那也很好。

Answer 1

事实证明，我必须在 where 子句之前移动 let 代码，然后将条件添加到 where。

比如

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();

可为空的对象必须在连接表查询中具有值

Nullable object must have a value in join tables query

c#

sql-server

entity-framework-core-2.1