Question

我有一些我正在尝试重构的linq代码，因为它不是很好：

基本上，我想知道是否有更好的方法来执行以下操作：

if (!string.IsNullOrWhiteSpace(_filter.AssignedTo)
{
var query = from ticket in dataClassesDataContext.TicketsIssues
            where ticket.ClosedDate == null 
            && cUser.GetUserNameUsingGUID(ticket.AssignTicketToUser) == _filter.AssignedTo                                                   
            select new
            {
                Priority = ticket.TicketPriority.TicketPriorityName,
                Description = ticket.Description.Replace("\n", ", "),
            };
}
else
{
var query = from ticket in dataClassesDataContext.TicketsIssues
            where ticket.ClosedDate == null 
            select new
            {
                Priority = ticket.TicketPriority.TicketPriorityName,
                Description = ticket.Description.Replace("\n", ", "),
            };
}

除了where子句检查AssignTicketToUser之外，它们都是相同的。

我希望有一个更好的方法来避免使用if else语句？我有一些这些代码块，不想复制很多代码！

Answer 1

var query = from ticket in dataClassesDataContext.TicketsIssues
            where ticket.ClosedDate == null 
            && (string.IsNullOrWhiteSpace(_filter.AssignedTo) ? true : cUser.GetUserNameUsingGUID(ticket.AssignTicketToUser) == _filter.AssignedTo)                                                   
            select new
            {
                Priority = ticket.TicketPriority.TicketPriorityName,
                Description = ticket.Description.Replace("\n", ", "),
            };

你可以完全摆脱if-else语句。将if条件转移到2nd where子句，并删除！。第二个where子句成为三元运算符。

如果条件为真，即如果_filter.AssignedTo为null，则不要通过返回true来测试_filter.AssignedTo。如果它不为null或为空，则继续执行原始else块中的子句。

Answer 2

一种方式可能是：

var query = from ticket in dataClassesDataContext.TicketsIssues
            where ticket.ClosedDate == null 
            select new
            {
                Priority = ticket.TicketPriority.TicketPriorityName,
                Description = ticket.Description.Replace("\n", ", "),
            };

if (!string.IsNullOrWhiteSpace(_filter.AssignedTo)
    query = query.Where(w => cUser.GetUserNameUsingGUID(w.AssignTicketToUser) == _filter.AssignedTo));

Answer 3

看看PredicateBuilder implementation from C# In a Nutshell，And方法应该以更通用的方式解决您的问题，并帮助建立对LINQ和表达式树的理解。你最终会得到类似的东西：

var query = from ticket in dataClassesDataContext.TicketsIssues
            where ticket.ClosedDate == null
            select new
            {
                Priority = ticket.TicketPriority.TicketPriorityName,
                Description = ticket.Description.Replace("\n", ", "),
            };

if (!string.IsNullOrWhiteSpace(_filter.AssignedTo))
{
     query = query.And(ticket => cUser.GetUserNameUsingGUID(ticket.AssignTicketToUser) == _filter.AssignedTo);
}

c＃linq where条件if

3 个答案: