How to extract a specific object from a JSON? - json

Question

I would like to know how to extract a specific object from a JSON.
I saw most of the problem solved on Stackoverflow before posting this, but there is no one who already talked about this.
I want need to get the slug value from the JSON objects.
Here is my code Get Users From JSON
Imports System
Imports Newtonsoft.Json.Linq
Public Module Module1
Public Sub Main()
Dim myJsonString = New System.IO.StreamReader(New System.Net.WebClient().
OpenRead("https://pastebin.com/raw/z4GZFuF3")).ReadToEnd()
Dim myJObject = JObject.Parse(myJsonString)
For Each match In myJObject("matches")
Console.WriteLine(match("id")("slug"))
Next
End Sub
End Module
And Here is the Output:
Run-time exception (line -1): Error reading JObject from JsonReader.
Current JsonReader item is not an object: StartArray. Path '', line 1, position 1.
Stack Trace:
[Newtonsoft.Json.JsonReaderException: Error reading JObject from JsonReader.
Current JsonReader item is not an object: StartArray. Path '', line 1, position 1.]
at Newtonsoft.Json.Linq.JObject.Load(JsonReader reader, JsonLoadSettings settings)
at Newtonsoft.Json.Linq.JObject.Parse(String json, JsonLoadSettings settings)
at Newtonsoft.Json.Linq.JObject.Parse(String json)
at Module1.Main()
What I have reduced since this error is that the object "matches" does not exist in the JSON text, but I have no idea what I should specify in its place to make this work.

Answer 1

The JSON that can be retrieved from the provided address:
(http://www.stginternational.org/wp-json/wp/v2/users)
is an array of Objects.
It can be parsed using JArray.Parse(), but I suggest to deserialize this JSON as .Net classes: it's much easier to handle.
The JSON's base object (each object in the array) is defined like this:
{
"id": 1,
"name": "drall",
"url": "",
"description": "",
"link": "http://www.stginternational.org/author/drall/",
"slug": "drall",
"avatar_urls": {
"24": "http://1.gravatar.com/avatar/dc6dd0ef71784957b629e124f19364cb?s=24&d=mm&r=g",
"48": "http://1.gravatar.com/avatar/dc6dd0ef71784957b629e124f19364cb?s=48&d=mm&r=g",
"96": "http://1.gravatar.com/avatar/dc6dd0ef71784957b629e124f19364cb?s=96&d=mm&r=g"
},
"meta": [],
"_links": {
"self": [
{
"href": "http://www.stginternational.org/wp-json/wp/v2/users/1"
}
],
"collection": [
{
"href": "http://www.stginternational.org/wp-json/wp/v2/users"
}
]
}
}
It can be represented by these .Net classes:
Public Class UserObject
Public Property Id As Long
Public Property Name As String
Public Property Url As String
Public Property Description As String
Public Property Link As Uri
Public Property Slug As String
<JsonProperty("avatar_urls")>
Public Property AvatarUrls As Dictionary(Of String, Uri)
Public Property Meta As List(Of Object)
<JsonProperty("_links")>
Public Property Links As Links
End Class
Public Class Links
Public Property Self As List(Of LinkCollection)
Public Property Collection As List(Of LinkCollection)
End Class
Public Class LinkCollection
Public property Href As Uri
End Class
With this model, you can simply use JsonConvert.DeserializeObject(), specifying the Type to deserialize to.
As mentioned, this is an Array or List of objects, where the base object is an UserObject, so you can specify a List(Of UserObject) :
Dim json = JsonConvert.DeserializeObject(Of List(Of UserObject))(json)
You can then access the class object as usual:
Imports System.Net
Imports Newtonsoft.Json
Dim users As List(Of UserObject) = Nothing
Using client As New WebClient()
Dim json = client.DownloadString([The URL])
users = JsonConvert.DeserializeObject(Of List(Of UserObject))(json)
End Using
If users IsNot Nothing Then
For Each user In users
Console.WriteLine(user.Slug)
Console.WriteLine(user.Links.Self(0).Href)
Console.WriteLine(user.Links.Collection(0).Href)
For Each avatar In user.AvatarUrls
Console.WriteLine($"Key: {avatar.Key}, Value: {avatar.Value}")
Next
Next
End If
In case you just want one of the properties (slug, in this case), you can use JArray.Parse() to parse the JSON and read the property value directly:
Using client As New WebClient()
Dim json = client.DownloadString([The URL])
Dim users = JArray.Parse(json)
For Each user As JToken In users
Console.WriteLine(user("slug"))
Next
End Using

Answer 2

While Jimi's answer is preferable because it deserializes the JSON into a strongly typed object, here is an alternative since you only care about getting a single property from the array of objects.
It does the following three steps:
Get the JSON from the endpoint
Convert the JSON literal into JArray
Use LINQ to get just the Slug item of each object in the array
Dim myJsonString = New System.IO.StreamReader(New System.Net.WebClient().OpenRead("http://www.stginternational.org/wp-json/wp/v2/users")).ReadToEnd
Dim arrayOfObjects = JArray.Parse(myJsonString)
Dim arrayOfSlugs = From jsonObject In arrayOfObjects Select jsonObject.Item("slug")
Example: Live Demo