[英]Avoiding excessive control flow working with Id arrays in MVC
MVC中的多选列表似乎没有绑定到复杂的模型。 相反,它们返回选定ID号的数组。
我在页面上有这样的控件,而让我不得不部署大量条件逻辑才能使我感到烦恼。 有问题的对象是一个Staff对象,可以拥有一个或多个团队的TeamMember成员身份。
我的对象来自实体框架。 我将此添加到Staff对象:
public int[] SelectedTeamMembers
{
get; set;
}
现在,我可以在视图中绑定到该属性,用户可以编辑多选列表。 在发回编辑表单时,我必须这样做(为清楚起见添加了注释):
//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,我可以通过将一点点耕种到某个功能上来整理一下,但是仍然感觉像是敲碎坚果的大锤。
有没有更整洁的方法来实现这一目标?
您应该评估将for
和foreach
循环合并为一个循环的可能性,以此作为简化此代码的第一步。
另外,您知道如何使用LINQ(如您的初始Where()
语句所证明的),因此也可以使用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);
});
}
尽管这并没有降低条件的复杂性(因为所有条件仍然存在),但语法更具可读性。
您可以通过这种方式进行操作...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; }
}
行动
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();
}
希望这可以帮助。
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