控制器中的存储库模式空引用异常

Question

我已经实现了通用存储库模式和UnitOfWork，但是当我尝试填充模型类的新实例时，控制器中出现了Null引用异常。

这是我的存储库模式：

class GenericRepository<TEntity> where TEntity : class
{
    internal PropmetEntities context;
    internal DbSet<TEntity> dbSet;

    public GenericRepository(PropmetEntities context)
    {
        this.context = context;
        this.dbSet = context.Set<TEntity>();
    }

    public virtual IEnumerable<TEntity> Get()
    {
        IQueryable<TEntity> query = dbSet;
        return query.ToList();
    }

    public virtual TEntity GetByID(object id)
    {
        return dbSet.Find(id);
    }

    public virtual void Insert(TEntity entity)
    {
        dbSet.Add(entity);
    }

    public virtual void Delete(object id)
    {
        TEntity entityToDelete = dbSet.Find(id);
        Delete(entityToDelete);
    }

    public virtual void Delete(TEntity entityToDelete)
    {
        if (context.Entry(entityToDelete).State == EntityState.Detached)
        {
            dbSet.Attach(entityToDelete);
        }
        dbSet.Remove(entityToDelete);
    }

    public virtual void Update(TEntity entityToUpdate)
    {
        dbSet.Attach(entityToUpdate);
        context.Entry(entityToUpdate).State = EntityState.Modified;
    }
}

这是我的工作单位：

class UnitOfWork 
{
    private PropmetEntities context = new PropmetEntities();
    private GenericRepository<User> userRepository;

    public GenericRepository<User> UserRepository
    {
        get
        {
            if (this.userRepository == null)
                this.userRepository = new GenericRepository<User>(context);
            return userRepository;
        }
    }
}

这是我的模型课：

public class UserGridModel
{
    public int ID { get; set; }
    public string Username {get; set;}
    public string EMail { get; set; }
    public string Surname { get; set; }
    public string Role { get; set; }
    public ContactInformation ContactInformation { get; set; }
    public Role Role1 { get; set; }
}

这是我的控制器操作：

private UnitOfWork.UnitOfWork unitOfWork = new UnitOfWork.UnitOfWork();

    [PrivilegeFilter(priv = Privileges.UserView)]
    public ActionResult Grid(GridSettings set)
    {
        var userList = from user in unitOfWork.UserRepository.Get() select user;
        var users = new List<UserGridModel>();
        if (userList.Any())
        {
            foreach (var user in userList)
            {
                users.Add(new UserGridModel()
                {
                    ID = user.ID,
                    Username = user.Username,
                    EMail = user.ContactInformation.EMail,
                    Surname = user.ContactInformation.Surname,
                    Role = user.Role1.Description
                });



            }
        }

        GridModel grid = new GridModel(set, users.Count());
        grid.rows = users.Skip((set.PageIndex - 1) * set.PageSize).Take(set.PageSize).ToList();
        return Json(grid, JsonRequestBehavior.AllowGet);

    }

我在这里得到一个空引用异常：

users.Add(new UserGridModel()
            {
                ID = user.ID,
                Username = user.Username,
                EMail = user.ContactInformation.EMail,
                Surname = user.ContactInformation.Surname,
                Role = user.Role1.Description
            });

Answer 1

您有该用户的ContactInformation吗？ 我的猜测是user.ContactInformation为null，并且在获取user.ContactInformation.Email时遇到错误。

Answer 2

可能的原因是user.ContactInformation == null或user.Role1 == null 。 您应该在UserGridModel创建代码中添加一些对null的检查。

Answer 3

您可以通过执行以下操作来null检查：

foreach (var user in userList.Where(x => x.ContactInformation != null && x.Role1 != null))
{
    users.Add(new UserGridModel()
    {
        ID = user.ID,
        Username = user.Username,
        EMail = user.ContactInformation.EMail,
        Surname = user.ContactInformation.Surname,
        Role = user.Role1.Description
    });
 }

当这些属性之一为null时，这至少将阻止您获取Null Reference Exception 。