在JavaScript中使用空C＃模型

Question

i'm trying to use my viewmodel from Razor in my script. The problem is that sometimes, my complex Model generated by EF which have cyclic values is null.

var skill = @Model.Skill1 != null ? "@Model.Skill1.SkillName" : "";

When the @Model.Skill1 is not null, i can use @Model.Skill1.SkillName. But if @Model.Skill1 is null the result is

Object reference not set to an instance of an object.

And the page is not even render.

It seem that @Model.Skill1.SkillName can't be write in the code even if the condition to access the property SkillName is not triggered.

So i tried to convert my object into a Json object but this time i have the cyclic values generating problem.

Any idea or way to bypass the problem?

Answer 1

You're mixing languages. If this is in your JavaScript block:

var skill = @Model.Skill1 != null ? "@Model.Skill1.SkillName" : "";

then you have two server-side statements there. With no logic determining whether or not to execute them. So they both execute, and the second one is a NullReferenceException .

Basically, you're trying to emit a null reference to the client and so the client can check if it's null. But by then you've already tried to dereference it, hence the error.

Conduct the null check server-side and just emit the result to the client-side code. Something like this:

var skill = '@(Model.Skill1 != null ? Model.Skill1.SkillName : "")';

Wrapping a value-emitting expression in parentheses in Razor @() means that the whole statement is server-side code and should result in a single emitted value.