Return Json object with Duplicate Keys using C#

Question

I\'m using WEB API to receive the request from the Client application to save the Contact Information and I need to send the Error Message only if data has an error otherwise no

Answer 1

You have a classic "XY" problem. You have asked "How do I do X", but you really need to do Y and you think that X is the only way to get to Y -- but X is either impossible or very hard. By changing your requirements a little, you can get to Y a different way, but you haven't seen that yet since you're stuck on X.

Here's your X: the JSON format that you want to get:

{
    "error" : {
        "SaveContactMethod":"FirstName Invalid",
        "SaveContactMethod":"LastName Invalid",
        "SaveContactMethod":"MiddleName Invalid"
    }
}

This will, as others have said, throw away all the error messages except for one when you load it into your C# code.

However, there's a very simple way to get all the error messages. You simply need to change the JSON you're expecting to look something like this instead:

{
    "error" : {
        "SaveContactMethod": [
            "FirstName Invalid",
            "LastName Invalid",
            "MiddleName Invalid"
        ]
    }
}

If you only had a single error message, you should still use a list:

{
    "error" : {
        "SaveContactMethod": [
            "FirstName Invalid"
        ]
    }
}

That way when you load the JSON into your C# code, it will always have the same type, Dictionary<string,List<string>>, whether there was one error or many.

That's the Y in your XY problem. Instead of beating your head against the wall of "I want to have duplicate keys in JSON", find a way around the wall: have a single key with a list of values. And now you can do what you really needed, which is to get all the error messages from your form with just a single key name for every single error message.

Answer 2

No, this is not possible.

This would be invalid* JSON:

{
    "error" : {
        "SaveContactMethod":"FirstName Invalid",
        "SaveContactMethod":"LastName Invalid",
        "SaveContactMethod":"MiddleName Invalid"
    }
}

You can check this here:

Warning:Duplicate key, names should be unique.[Code 23, Structure 9]
Warning:Duplicate key, names should be unique.[Code 23, Structure 13]

_{*Depending on what you call valid}

_{If you realy want to go this route, according to RFC 4627, you could use the StringBuilder class.}

---

Since you don't seem to understand, what Depending on what you call valid means.

ECMA-262:

In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.

That means: If you get three SaveContactMethod's, you only want "MiddleName Invalid" in ECMA Script (JS). With c# serialization, this would not even be possible. You need to write your own JsonSerializer for it.