How to I read a json file containing array with C# and perform LINQ query on it?

Question

I am new on json in C#. I use newtonsoft.json I have a json file with data (array):

[ 
    {
         "firstName": "Joyce",
         "lastName": "Huff",
         "isActive": true,
         "age": 59,
         "gender": "female",
         "eyeColor": "green",
         "friends": [
                        "Kendra Buck"
                    ]
   },
   {
        "firstName": "Diann",
        "lastName": "Patrick",
        "isActive": true,
        "age": 45,
        "gender": "female",
        "eyeColor": "blue",
        "friends": [
                      "Roach Mills",
                      "Diaz Pickett"
                   ]
   },
   {
       "firstName": "Holt",
       "lastName": "Erickson",
       "isActive": false,
       "age": 53,
       "gender": "male",
       "eyeColor": "brown",
       "friends": [
                    "Lindsay Wyatt",
                    "Freeman Mcfadden",
                    "Matilda Franklin"
                  ]
  },
  {
      "firstName": "Crystal",
      "lastName": "Santiago",
      "isActive": false,
      "age": 31,
      "gender": "female",
      "eyeColor": "brown",
      "friends": [
                   "Stacy Joseph"
                 ]
   }
]

How to I read a json file containing array with C# and perform LINQ query on it? I found example on JObject to read json from file but I could not figure it out how do I handle json array. After reading json array, I would like to run query like: select count(*) from person where age>40;

Please suggest me. Thank you in advance.

https://www.newtonsoft.com/json/help/html/QueryingLINQtoJSON.htm — BehrouzMoslem, Mar 14 '18 at 09:22
@BehrouzMoslem the link you provided, I visited already, It shows the JObject not JArray — aliceangel, Mar 14 '18 at 09:26
[Here is the same question and answer](https://stackoverflow.com/questions/16339167/c-sharp-net-how-to-deserialize-complex-object-of-json) — Yaroslav N., Mar 14 '18 at 09:27
@Sabrina you can easily use JArray instead of JObject and that's shown in most links. Even JObject works, it returns an object that contains an arrya. What have you tried anyway? — Panagiotis Kanavos, Mar 14 '18 at 09:28
@PanagiotisKanavos I tried with JArray but I got array key/value problem, my program runs but no output is shown. It would be really very helpful, if you provide any code example. — aliceangel, Mar 14 '18 at 09:33
@Sabrina arrays don't have keys. Dictionaries and objects do. Unless you deserialize to concrete classes you'll have to juggle keys anyway. Post your code. Can't even give an example of fixing your code if you don't post it — Panagiotis Kanavos, Mar 14 '18 at 09:35
@Sabrina why don't you deserialize the string to concrete classes anyway? — Panagiotis Kanavos, Mar 14 '18 at 09:35
@YaroslavN. my question is not exactly the same as you provided — aliceangel, Mar 14 '18 at 09:35
@PanagiotisKanavos I will try the first answer given by Alex. — aliceangel, Mar 14 '18 at 09:38

Alex · Accepted Answer · 2018-03-14T09:38:37.840

7

Define model:

public class Person
{
    public string firstName { get; set; }
    public string lastName { get; set; }
    public bool isActive { get; set; }
    public int age { get; set; }
    public string gender { get; set; }
    public string eyeColor { get; set; }
    public List<string> friends { get; set; }
}

Read and deserialize JSON:

string json = System.IO.File.ReadAllText("test.json");
var people = Newtonsoft.Json.JsonConvert.DeserializeObject<List<Person>>(json);

Perform LINQ query:

var peopleOverForty = from p in people
                      where p.age > 40
                      select p;

edited Mar 14 '18 at 09:38

answered Mar 14 '18 at 09:27

Alex

1,433
9
18

Thank you very much for giving me an example. Can you please explain me if the json array data is coming from web api continuously and the size is really large like gigabyte, how could I handle it? – aliceangel Mar 14 '18 at 09:41

Vulpex · Answer 2 · 2018-03-14T10:23:16.397

I would suggest creating a Class for the Object you're trying to read, if possible at least.

Then I would deserialize the JSON String to an List<T>where T euqals your Modelclass.

List<YourObject> deserializedObject = JsonConvert.DeserializeObject<YourObject>(jsonString);

Wit this list you can then easily perform LINQ queries like

List<YourObject> selectedObjects = deserializedObject.Where(x => x.age > 31);

This gives you the object selectedObjects with only containing Objects where age > 31.

How to I read a json file containing array with C# and perform LINQ query on it?

2 Answers2

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