MVC中的多选列表似乎与复杂模型绑定。相反,它们返回一组选定的Id编号。
我在页面上有这样的控件,我对为了让它工作而必须部署的条件逻辑的数量感到恼火。有问题的对象是一个Staff对象,其TeamMember成员资格可以是任何一个或多个团队。
我的对象来自实体框架。我将此添加到Staff对象:
public int[] SelectedTeamMembers
{
get; set;
}
我现在可以在我的视图中绑定到此属性,用户可以编辑多选列表。在回发编辑表格时,我必须这样做(为了清楚起见添加了评论):
//user.TeamMembers not bound, so get existing memberships
IEnumerable<TeamMember> existingTeamMembers = rep.TeamMembers_Get().Where(t => t.UserId == user.UserID);
//if array is empty, remove all team memberships & avoid null checks in else
if(user.SelectedTeamMembers == null)
{
foreach(TeamMember tm in existingTeamMembers)
{
rep.TeamMembers_Remove(tm);
}
}
else
{
// if team members have been deleted, delete them
foreach (TeamMember tm in existingTeamMembers)
{
if (!user.SelectedTeamMembers.Contains(tm.TeamId))
{
rep.TeamMembers_Remove(tm);
}
}
// if there are new team memberships, add them
foreach (int i in user.SelectedTeamMembers)
{
if (!existingTeamMembers.Select(t => t.TeamId).Contains(i))
{
TeamMember tm = new TeamMember { TeamId = i, UserId = user.UserID };
rep.TeamMembers_Change(tm);
}
}
}
当然,我可以通过将每一部分分解成一个功能来整理这一点,但它仍然感觉像是一个大锤来破解坚果。
是否有更简洁的方法来实现这一目标?
答案 0 :(得分:2)
作为简化此代码的第一步,您应该评估将for
和foreach
循环组合到一个循环中的可能性。
此外,您知道如何使用LINQ(由初始Where()
语句证明),因此使用LINQ及其一些辅助扩展来简化null
条件操作:
//user.TeamMembers not bound, so get existing memberships
IEnumerable<TeamMember> existingTeamMembers = rep.TeamMembers_Get().Where(t => t.UserId == user.UserID);
//if array is empty, remove all team memberships & avoid null checks in else
if(user.SelectedTeamMembers == null)
{
existingTeamMembers.ToList().ForEach(tm => rep.TeamMembers_Remove(tm));
}
else
{
// if team members have been deleted, delete them
existingTeamMembers.Where(tm => !user.SelectedTeamMembers.Contains(tm.TeamId)).ToList().ForEach(tm => rep.TeamMembers_Remove(tm));
// if there are new team memberships, add them
user.SelectedTeamMembers.Except(existingTeamMembers.Select(t=> t.TeamId)).ToList().ForEach(i =>
{
TeamMember tm = new TeamMember { TeamId = i, UserId = user.UserID };
rep.TeamMembers_Change(tm);
});
}
虽然这并未降低条件复杂性(因为所有条件仍然存在),但语法更具可读性。
答案 1 :(得分:0)
你可以这样做......它依赖于使用RemoveRange
方法。
实体 - 我将自己用于演示目的
public class User
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid Id { get; set; }
public String Name { get; set; }
}
<强>动作强>
public ActionResult Action(Guid[] selectedTeamMembers)
{
using (var ctx = new DatabaseContext())
{
//
// Start by targeting all users!
//
var usersToRemove = ctx.Users.AsQueryable();
//
// if we have specified a selection then select the inverse.
//
if (selectedTeamMembers != null)
{
usersToRemove = usersToRemove.Where(x => !selectedTeamMembers.Contains(x.Id));
}
//
// Use the Set Generic as this gives us access to the Remove Range method
//
ctx.Set<User>().RemoveRange(usersToRemove);
ctx.SaveChanges();
}
return View();
}
希望这有帮助。