Question

我正在使用ExpressMapper将Linq-To-Sql对象映射到另一个对象 - 但是我的字符串中的空值导致了问题。有没有办法从ExpressMapper中将这些空值转换为string.Empty？

E.g。鉴于以下类别：

class A
{
    string a = null;
}

class B
{
    string a;
}

进行转换时

B b = Mapper.Map<A, B>(new A(), new B());

我想b.a == ""而不是b.a == null

Answer 1

您可以使用helloworld.c功能：

xb@dnxb:/tmp/c c$ gdb -q /tmp/c\ c/main 
expansion:  History expansion on command input is on.
filename:  The filename in which to record the command history is "/home/xiaobai/.gdb_history".
remove-duplicates:  The number of history entries to look back at for duplicates is 0.
save:  Saving of the history record on exit is on.
size:  The size of the command history is 10000000.
Reading symbols from /tmp/c c/main...done.
(gdb) my
Breakpoint 1 at 0x40063a: file main.c, line 5.

Breakpoint 1, main () at main.c:5
5               hello();
(gdb) sn

[customStepping]


******************** /usr/src/glibc/glibc-2.24/sysdeps/unix/sysv/linux/_exit.c /tmp/c c/main.c ********************
hello () at helloworld.c:3
3         printf("Hello world!\n");
(gdb) 

[customStepping]


******************** /tmp/c c/helloworld.c ********************
File #1 [Stepping] Disabled 
Hello world!
4         printf("Next line\n");
(gdb) 

[customStepping]


******************** /tmp/c c/helloworld.c ********************
File #1 [Stepping] Disabled 
Next line
5       }
(gdb) 

[customStepping]


******************** /tmp/c c/helloworld.c ********************
File #1 [Stepping] Disabled 
main () at main.c:6
6               return 0;
(gdb) 

[customStepping]


******************** /tmp/c c/main.c ********************
7       }
(gdb) 

[customStepping]


******************** /tmp/c c/main.c ********************
__libc_start_main (main=0x400636 <main>, argc=1, argv=0x7fffffffd468, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, 
    stack_end=0x7fffffffd458) at ../csu/libc-start.c:325
325       exit (result);
(gdb) 
...

Answer 2

您可以使用null-coalescing operator。

string a = "";
string b = null;

string c = a ?? "xyz"; //a is not null, so empty string is assigned to c
string d = b ?? "xyz"; //b is null, so "xyz" is assigned to d

通过这种方式，您可以简化对此的调用：

B b = Mapper.Map<A, B>(new A(), new B());
b.a = b.a ?? "";
//"" can be String.Empty, whichever you prefer for your code style.

ExpressMapper - null到string.Empty

2 个答案: