How to propogate null instance in C#/MVC without If/Else or Try/Catch?

Question

I have an entry in Razor View which is

<li data-img-url="@stock["images"][0]["url"]">
@* stock is a JObject which can contain or cannot contain ["images"]*@

Irrespective of location of null occurence, how to get the final string data-img-url="". Also how to handle such situations where output of statement is needed without adding extra code blocks such as If/Else or Try/Catch

Just create a function that gets the URL and has the if/else logic in it. — DavidG, Oct 15 '19 at 09:46
I am using the null-propagating operator to avoid accessing null object properties and variables hence avoiding the null reference exception — Conrad, Oct 15 '19 at 10:16

score 2 · Accepted Answer · answered Oct 15 '19 at 10:11

JObject has a SelectToken method which you can utilize for your scenario.

  JObject jsonDoc = JObject.Parse(json);

  Console.WriteLine(jsonDoc.SelectToken("images[0].url"));

Here you will find reference code for SelectToken

SelectToken will return empty if no token found and return results if its a valid result

score 1 · Answer 2 · answered Oct 15 '19 at 09:54

In just C#, the null-propagating operator can help here, i.e.

var x = obj?["bar"];

note however that this only deals with nulls; it won't help you if the problem is a KeyNotFoundException (because obj isn't null, but there's no key "bar"). So: in the general case: just write a method that does what you need, and which also makes everything cleaner; this could be an extension method on whatever stock is, noting that extension methods do not null check on the this argument:

public static string GetFrob(this Stock stock, string grapple, int foo, string blap)
{...}

...

<li data-img-url="@stock.GetFrob("images", 0, "url")">

score 0 · Answer 3 · answered Oct 15 '19 at 09:57

0

I do not know if I have understood the question well, but according to what you want to do you have to put an if:

@(stock["images"][0]["url"] == null ? "" : stock["images"][0]["url"])

it is an if, but with linear syntax

answered Oct 15 '19 at 09:57

Ahmed Msaouri

316
1
10

score 0 · Answer 4 · answered Oct 15 '19 at 10:24

0

Use a ternary:

<li data-img-url="@(stock["images"][0]["url"]! = null:stock["images"][0]["url"]:"""> @* stock is a JObject which can contain or cannot contain ["images"]*@

If the doesn't work, encase the entire attribute in the ternary.

answered Oct 15 '19 at 10:24

Ashmosis

1

How to propogate null instance in C#/MVC without If/Else or Try/Catch?

4 Answers4