Cannot deserialize the current JSON array (e.g. [1, 2, 3]) into type help me

Question

1.00/5 (1 vote)

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JavaScript

[
	{	"id" : "hoho1"
		"pw" : "08217"
		"name" : "Potter"
	},
	{	"id" : "hoho2"
		"pw" : "1677"
		"name" : "Kane"
	},
	{	"id" : "hoho3"
		"pw" : "1541",
		"name" : "Moody"
	},
	{	"id" : "hoho4"
		"pw" : "0510"
		"name" : "christina"
	},
]

-------------------------------------------------------

C#

public class Employee
{
    public string id { get; set; }
    public string pw { get; set; }
    public string name { get; set; }
}

-------------------------------------------------------

C#

StreamReader r = new StreamReader("user.json");
string sc = r.ReadToEnd();  

Employee m = JsonConvert.DeserializeObject<Employee>(sc);

-------------------------------------------------------

C#

if (ID.Text == m.id && PW.Text == m.pw)
{
	MessageBox.Show("Login Success");

	this.Hide();
	Form2 Form = new Form2();
	Form.Show();
}
else
{
	MessageBox.Show("Login Failed");
}

What I have tried:

This is first time to programming.

I write code like that but
I got "Cannot deserialize the current JSON array (e.g. [1,2,3]) into type Exception code.
I want to know How to work?

Posted 20-Sep-23 18:36pm

Member 16097205

Updated 20-Sep-23 20:06pm

Graeme_Grant

v4

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2 solutions

Solution 2

C#

Employee m = JsonConvert.DeserializeObject<employee>(sc);

Above you're saying that there is only 1 item, not a list of items. Use:

C#

List<Employee> m = JsonConvert.DeserializeObject<List<Employee>>(sc);

UPDATE: Here is a working example using the answer above:

C#

using Newtonsoft.Json;

string rawJson = @"[ { ""id"" : ""hoho1"",
""pw"" : ""08217"",
""name"" : ""Potter""
},
{ ""id"" : ""hoho2"",
""pw"" : ""1677"",
""name"" : ""Kane""
},
{ ""id"" : ""hoho3"",
""pw"" : ""1541"",
""name"" : ""Moody""
},
{ ""id"" : ""hoho4"",
""pw"" : ""0510"",
""name"" : ""christina""
}
]";

List<Employee> results = JsonConvert.DeserializeObject<List<Employee>>(rawJson);

foreach (var item in results)
    Console.WriteLine($"id: {item.id} | pw: {item.pw} | name: {item.name}");

Console.ReadKey();

public class Employee
{
    public string id { get; set; }
    public string pw { get; set; }
    public string name { get; set; }
}

NOTE: The above code is for a .Net 7.0 console app. Same applies to .Net Framework 4.8 and earlier, just needs to be wrapped in a standard console app.

And the output:

id: hoho1 | pw: 08217 | name: Potter
id: hoho2 | pw: 1677 | name: Kane
id: hoho3 | pw: 1541 | name: Moody
id: hoho4 | pw: 0510 | name: christina

Posted 20-Sep-23 19:16pm

Graeme_Grant

Updated 20-Sep-23 20:00pm

v2

Comments

Graeme_Grant 21-Sep-23 1:56am

the issue is not with my answer. I'll post a full example with output.

Member 16097205 21-Sep-23 5:48am

Then I have compile Error that There is no 'm' in current context. How can I use m?

Graeme_Grant 21-Sep-23 5:52am

This is programming 101... it depends on where you declared it and where you are using it. Move the declaration to where you need it.

Here are a couple of links that cover this topic in more detail for beginners like yourself:
* Variable Scopes in C#[^]
* Control variable scope and logic using code blocks in C# - Training | Microsoft Learn[^]

Graeme_Grant 21-Sep-23 6:27am

Please do not post code in comments.

What you are asking me to do is outside of the scope of Quick Answers forum. I have given you pointers to training materials to answer your variable scope issue causing your compile-time error. Now you need to roll up your sleeves and do some reading, learning and possibly more research. Good luck with it.

Dave Kreskowiak 21-Sep-23 9:30am

It doesn't work because you don't know how any of the individual statements work. You have no clue what variable scope is, nor what the individual variables represent at any point during execution.

This all comes down to a complete lack of understanding that you are going to need books and classes to get through. NOT A FORUM ENVIRONMENT. These text boxes are way too small to type small books into to teach you everything you need to know just to get this little bit of code to work.

CPallini 21-Sep-23 2:24am

5.

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OriginalGriff · Accepted Answer · 2023-09-20T18:52:00

Solution 1

That's because your JSON is not valid - it doesn't follow the rules for JSON: JSON Introduction[^]

JSON

[ { "id" : "hoho1"
"pw" : "08217"
"name" : "Potter"
},
{ "id" : "hoho2"
"pw" : "1677"
"name" : "Kane"
},
{ "id" : "hoho3"
"pw" : "1541",
"name" : "Moody"
},
{ "id" : "hoho4"
"pw" : "0510"
"name" : "christina"
},
]

You need to separate each item with commas:

JSON

[ { "id" : "hoho1",
"pw" : "08217",
"name" : "Potter"
},
{ "id" : "hoho2",
"pw" : "1677",
"name" : "Kane"
},
{ "id" : "hoho3",
"pw" : "1541",
"name" : "Moody"
},
{ "id" : "hoho4",
"pw" : "0510",
"name" : "christina"
}
]

Posted 20-Sep-23 18:52pm

OriginalGriff

Comments

Member 16097205 21-Sep-23 0:57am

OK, I separate each item with commas then,
but I got same exception code too.

Is there any error about
StreamReader r = new StreamReader("user.json");
string sc = r.ReadToEnd();

Employee m = JsonConvert.DeserializeObject<employee>(sc); ??

I'm beginner of programming.
I need your help!!

OriginalGriff 21-Sep-23 1:52am

Well, there are several things wrong with it, but as far as "processing JSON" goes they are not relevant: the file is stored in the wrong place so it will fail in production, the passwords are in clear text so you will get MASSIVE fines from the EU because you ignored GDPR, and your naming conventions are a poor choice.

The code itself won't work (provided you edited the JSON correctly, but I can't access your HDD to tell that! :D ) because:
1)An Employee is not the same as an employee - C# is case sensitive!
2) You aren't deserializing a single Employee instance, you are reading a collection of Employees - so you need to tell NewtonSoft that:

List<Employee> employees = JsonConvert.DeserializeObject<List<Employee>>(sc);

OriginalGriff 21-Sep-23 6:18am

Have you ever heard of loops?

Member 16097205 21-Sep-23 6:25am

for() or foreach()?
I heard that.

OriginalGriff 21-Sep-23 6:34am

Come on man, this is basic stuff. If you can't work out "Oh, I need a loop" and "I'll use a ??? loop" for yourself, then you have very, very little chance of getting your project off the ground at all - and what you do produce will be horrendous: bloated, unreliable, hard to maintain, and very, very prone to you getting fined.

Shelve this - back it up somewhere so you can look at it later - and go back to the beginning with a course or a book and learn the basics properly before starting again. Then in six months time, drag out this project and squirm in horror at the monstrosity you were bolting together so hopefully ... :laugh:

OriginalGriff 21-Sep-23 9:21am

"t's easy to solve exception for you, but I'm not. lol.
can you know me code to solve this exception?"
No, I can't - the exception happens because of something you aren't telling us: if I copy your code as modified below:

            StreamReader r = new StreamReader(@"D:\Temp\user.json");
            string sc = r.ReadToEnd();
            List<Employee> employees = JsonConvert.DeserializeObject<List<Employee>>(sc);

and create a user.json file containing the JSON as modified by me originally, it runs without an exception: I get a collection of four Employee instances as I would expect, and the debugger shows me that it all worked fine.

Now, I can't believe that you can't cope with editing your code, so my guess - and that's all it can be without access to your files - is that you are picking up the wrong file, editing the wrong file, or doing something else in code that I can't see.

So no, I can't tell you "do this" and it'll be fixed - it needs you to know what you are doing and without meaning to be cruel or nasty you aren't showing any signs of that at the moment!

"Why everybody always say that it is easy so you study yourself? lol."
Because if you study it properly, it really is - but that doesn't mean "guess and hope it's right" or "find the code on the internet and hope that works"! It means following a course, or getting a book and reading it cover to cover, plus doing the exercises to make sure it "goes into your brain" correctly.

"Can you teach me next monday if I can't solve this exception?"

:laugh:
No - partly because I'm not a teacher, partly because I can't see when your eyes start to glaze over, partly because I have a lot to do in order to get paid (this site is all volunteers), but mostly because those books I mentioned tend to run well over a thousand pages and even I can't read that fast! :D

Member 16097205 21-Sep-23 22:31pm

OK. Thank your for response about my question.
what I cand do is just give up this exception and make other Program.
I'll study harder so that I'll teach someone to help this code.
I think this exception is hard to me.
Just What I can do is study harder!!
Thank you for your time!!

OriginalGriff 22-Sep-23 1:08am

Don't give up on it, use the debugger to find out why it's happening!
Look at what is in the string you pass to Newtonsoft, look at where the exception happens. This is a tiny piece of code, so learning to debug on it is fairly easy (even if it looks really difficult from your current position.)

My guess is that you are editing the wrong use.json file - so changes you make aren't reflected in the app when it runs - and since you are using the current directory to access it that's entirely feasible. The debugger can tell you exactly what was in the file, so use it to find out.
This isn't difficult; you have the tools you need - just not the "mental attitude" to look at the problem yet, and until you do develop that skill you are going to come across similar "unsolvable" problems in every project you try!

Member 16097205 24-Sep-23 21:12pm

Oh, I solve it using for() loops that you advise me!
I feel fly away!
Next step is using DB, and write SQL query.
Have a nice day

CPallini 21-Sep-23 2:24am

5.