如何在正确处理NULL值的同时在LINQ中连接字符串

Question

我想要一种使用LINQ将多个列连接在一起的优雅方法,但是当任何列为NULL时使用+运算符或concat()会导致连接后的值为NULL.

有没有类似于concat()以不同的方式处理NULL,或者我是否以不正确的方式考虑这个？

任何帮助表示赞赏!

这是我正在使用的代码:

List<CustomObject> objects = (
    from obj in ObjectTable
    where obj.Id == Id
    select new CustomObject()
    {
        EnteredBy = obj.EnteredBy, 
        EntryDate = obj.EntryDate, 
        WorknoteText = 
            obj.VchWorkNote1 +
            obj.VchWorkNote2 + 
            obj.VchWorkNote3 +
            obj.VchWorkNote4 +
            obj.VchWorkNote5 +
            obj.VchWorkNote6 +
            obj.VchWorkNote7 +
            obj.VchWorkNote8 +
            obj.VchWorkNote9 +
            obj.VchWorkNote10 +
            obj.VchWorkNote11 +
            obj.VchWorkNote12 +
            obj.VchWorkNote13 +
            obj.VchWorkNote14 +
            obj.VchWorkNote15 +
            obj.VchWorkNote16 +
            obj.VchWorkNote17 +
            obj.VchWorkNote18 +
            obj.VchWorkNote19 +
            obj.VchWorkNote20
    }).ToList();

Answer 1

一种选择是使用null合并运算符:

List<CustomObject> objects = (from o in ObjectTable
                              where o.Id == Id
                              select new CustomObject(){
                              EnteredBy = o.EnteredBy, 
                              EntryDate = o.EntryDate, 
                              WorknoteText = 
                              (o.VchWorkNote1 ?? "") +
                              (o.VchWorkNote2 ?? "") + 
                              (o.VchWorkNote3 ?? "") +
                              (o.VchWorkNote4 ?? "") +
                              ...
                              (o.VchWorkNote20 ?? "")
                              }).ToList();

希望生成的SQL将使用适当的转换.