How do you search a JSON file in C# to find a specific value?

Question

I have a json file that looks like this:

{
  "id": 1,
  "FirstName": "jen",
  "LastName": "may",
  "UserName": "jenmay",
  "Password": "august",
  "securityQ1": "leeds",
  "securityQ2": "smith"
}{
  "id": 2,
  "FirstName": "lucy",
  "LastName": "reed",
  "UserName": "lucyreed1",
  "Password": "bucket",
  "securityQ1": "manchester",
  "securityQ2": "bow"
}

I want to read the file to check that a username and password match a users input. I have the input as uname and pword.

I first attempt to deserialize the JSON.

public List<User> DeserializedUsersList(string json)
        {
            List<User> user = JsonConvert.DeserializeObject<List<User>>(json);
            return user;
        }

it keeps throwing me a 'Newtonsoft.Json.JsonSerializationException' exception.

I'm really new to C# and I'm not sure how to find username in the file. Then check that password matches the inputted password. How should I go about this?

Thank you!

Can you add more information about the exception? Looking the file content you posted, there are two errors: 1) Array in JSON reqires the [] that are missing 2) Between the elements, a comma is needed (in your post there is no comma betweens the data of the two users) — PiGi78
– PiGi78, Commented Dec 13, 2020 at 21:20

Jawad · Accepted Answer · 2020-12-13 21:20:30Z

3

Your JSON is a bit off, meaning, you're missing commas between objects and square brackets around it. If it is an array of objects, you can use Linq to query specific user.

[{
  "id": 1,
  "FirstName": "jen",
  "LastName": "may",
  "UserName": "jenmay",
  "Password": "august",
  "securityQ1": "leeds",
  "securityQ2": "smith"
},{
  "id": 2,
  "FirstName": "lucy",
  "LastName": "reed",
  "UserName": "lucyreed1",
  "Password": "bucket",
  "securityQ1": "manchester",
  "securityQ2": "bow"
}
]

and your code would look something like this,

var user = JsonConvert.DeserializeObject<List<User>>(json);
var selectedUser = user.Where(x => x.UserName.Equals("jenmay")).FirstOrDefault();

answered Dec 13, 2020 at 21:20

Jawad

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Kalten · Accepted Answer · 2020-12-13 22:55:05Z

Json.Net support multiple content deserialization when using underlying JsonTextReader class.

var json = @"
{""id"": 1,""FirstName"": ""jen"",""LastName"": ""may"",""UserName"": ""jenmay"",""Password"": ""august"",""securityQ1"": ""leeds"",""securityQ2"": ""smith""}
{""id"": 2,""FirstName"": ""lucy"",""LastName"": ""reed"",""UserName"": ""lucyreed1"",""Password"": ""bucket"",""securityQ1"": ""manchester"",""securityQ2"": ""bow""}";


var jsonSerializer = new JsonSerializer();
using var reader = new JsonTextReader(new System.IO.StringReader(json));
reader.SupportMultipleContent = true;

var users = new List<User>();
while (reader.Read())
{
    var item = (User)jsonSerializer.Deserialize(reader, typeof(User));
    users.Add(item);
}

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