如何在LINQ中连接字符串，同时正确处理NULL值 [英] How to concat strings in LINQ while properly dealing with NULL values

问题描述

我想使用LINQ将多个列连接在一起的一种优雅方法，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.

I'd like an elegant way to concatenate several columns together using LINQ, but using the + operator or concat() when any of the columns are NULL results in NULL for the value after concatenation.

是否存在类似于concat()的其他处理NULL的东西，或者我是否以错误的方式考虑了此问题?

Is there anything similar to concat() that handles NULL differently, or am I thinking about this in the incorrect way?

感谢您的帮助！

这是我正在使用的代码:

Here is the code I am using:

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();

推荐答案

一种选择是使用空合并运算符:

One option is to use the null coalescing operator:

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将使用适当的翻译.

Hopefully the generated SQL will use an appropriate translation.

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