How to check and throw a Exception if duplicate values exist in a JSON file

Question

My JSON file:

[
  {
    "nome": "Marcos",
    "pontos": 12,
    "acesso": "2016-04-22T21:10:00.2874904-03:00"
  },
  {
    "nome": "Felipe",
    "pontos": 12,
    "acesso": "2016-04-22T21:10:00.2904923-03:00"
  },
  {
    "nome": "Augusto",
    "pontos": 15,
    "acesso": "2016-04-22T21:10:00.2909925-03:00"
  },
  {
    "nome": "Augusto",
    "pontos": 12,
    "acesso": "2016-04-22T21:10:00.2909925-03:00"
  }
]

The "nome" values must all be unique; which scan should I do? Go through the array and compare to see if it already exists? I'm currently using Newtonsoft.Json; is there any helper function for this?

This question has already been answered before http://stackoverflow.com/questions/3877526/json-net-newtonsoft-json-two-properties-with-same-name http://stackoverflow.com/questions/12806080/json-net-catching-duplicates-and-throwing-an-error — JazzCat, Apr 23 '16 at 00:29
@JazzCat Those questions deal with duplicate *keys* in the JSON, whereas this question seems to be asking about duplicate *values* — Brian Rogers, Apr 23 '16 at 00:38

Brian Rogers · Answer 1 · 2016-04-23T01:09:28.443

1

One easy way to generate an exception if there are duplicate values is to try to put them into a dictionary:

JArray array = JArray.Parse(json);

// This will throw an exception if there are duplicate "nome" values.
array.Select(jt => jt["nome"]).ToDictionary(jt => (string)jt);

Here is a working demo: https://dotnetfiddle.net/FSuoem

edited Apr 23 '16 at 01:09

answered Apr 23 '16 at 01:02

Brian Rogers

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score 0 · Answer 2 · answered Apr 23 '16 at 00:42

your problem is very specific. Because you need first do a parse of your Json data first. I recommend you to use System.Collections.Generic.HashSet to validate such rule.

//...
// Here you do your Json parse with you library:
//Then you need to iterate into the object adding those name values into a HashSet:
System.Collections.Generic.HashSet<String> names = new System.Collections.Generic.HashSet<string> ();
foreach (string name in ITERATE_HERE) {
    if (names.Contains (name)) {
        throw new System.ArgumentException("The name value need to be unique.", "some rule");
    }
    names.Add (name);
}
//...

So, i hope that may can help you.

score 0 · Accepted Answer · answered Apr 23 '16 at 01:07

Assuming you have a model for your JSON input like so:

public class Model {
    public string Nome { get; set; }
    public string Pontos { get; set; }
    public DateTime Acesso { get; set; }
}

It becomes quite easy to determine if duplicates are found.

var deserialized = JsonConvert.DeserializeObject<List<Model>>(json);

if (deserialized.Select(x => x.Nome).Distinct().Count() != deserialized.Count) {
    throw new Exception("Duplicate names found");
}

We know there are duplicates if the number of objects in our deserialized list is not equal to the number of distinct names we selected from the same list.

How to check and throw a Exception if duplicate values exist in a JSON file

3 Answers3