为什么在 Ef 核心数据读取器中打开我的连接

Question

我是新手。对我放轻松。
这是我的操作代码

[HttpGet]
    public async  Task<IActionResult> EditRole(string id)
    {
        var role = await roleManager.FindByIdAsync(id);
        if(role == null)
        {
            ViewBag.ErrorMessage = $"Role with Id = {id} cant be found";
            return View("NotFound");
        }

        var model = new EditRoleViewModel()
        {
            Id = role.Id,
            RoleName = role.Name
        };

        foreach(var user in userManager.Users)
        {
            try
            {
                if (await userManager.IsInRoleAsync(user, role.Name))
                {
                    model.Users.Add(user.UserName);
                }
            }
            catch (Exception ex)
            {

                throw;
            }
            
        }

        return View(model);
    }

并且在检查我的用户是否处于此角色时抛出此异常

{"There is already an open DataReader associated with this Connection which must be closed first."}

Answer 1

由此变化：

 foreach(var user in userManager.Users)
        {
            try
            {
                if (await userManager.IsInRoleAsync(user, role.Name))
                {
                    model.Users.Add(user.UserName);
                }
            }
            catch (Exception ex)
            {

                throw;
            }
            
        }

为此：

var users = userManager.Users.ToList();

 foreach(var user in users)
        {
            try
            {
                if (await userManager.IsInRoleAsync(user, role.Name))
                {
                    model.Users.Add(user.UserName);
                }
            }
            catch (Exception ex)
            {

                throw;
            }
            
        }

将 userManager.Users 放在 foreach 循环上会创建一个连接以从数据库中检索用户，并且在完成之前不会关闭，然后当您调用 userManager.IsInRoleAsync 时已经有一个连接打开分贝。