json.net Deserialise to array of objects c#

Question

I have a POCO class which looks like this:

public class Item : Asset
{
    public int PlaylistId { get; set; }
    public int AssetId { get; set; }
    public double Duration { get; set; }
    public int Order { get; set; }
}

and Asset looks like this:

public enum AssetType
{
    Image = 1,
    Video,
    Website
}

public class Asset
{       

    public int Id { get; set; }
    public string Name { get; set; }
    public string Filename { get; set; }
    public AssetType Type { get; set; }
    public string CreatedById { get; set; }
    public string ModifiedById { get; set; }
    [Display(Name="Created by")] public string CreatedBy { get; set; }
    [Display(Name="Modified by")] public string ModifiedBy { get; set; }
}

and then I have a json file which looks like this:

{
   "Items":[
      {
         "PlaylistId":1,
         "Type":2,
         "Duration":19,
         "Filename":"stream1_mpeg4.avi"
      },
      {
         "PlaylistId":1,
         "Type":2,
         "Duration":21,
         "Filename":"stream2_mpeg4.avi"
      }
   ]
}

and finally I have my code which looks like this:

public IList<Item> GetAll()
{
    if (File.Exists(itemsPath))
    {
        using (var fs = new FileStream(itemsPath, FileMode.Open))
        using (var sr = new StreamReader(fs))
        {
            var text = sr.ReadToEnd();
            var array = JsonConvert.DeserializeObject<Item[]>(sr.ReadToEnd());
            return array.ToList();
        }
    }
    else
        throw new FileNotFoundException("Unable to find the playlist, please make sure that " + itemsPath + " exists.");
}

The text variable contains the correct json string as I would expect, but the array is null, therefore array.ToList(); throws an error. Does anyone know what I am doing wrong?

Cheers in advance /r3plica

digEmAll · Accepted Answer · 2013-10-07 12:51:45Z

3

You're calling ReadToEnd() twice, so the second time there's no more text to read on the stream:

var text = sr.ReadToEnd();
var array = JsonConvert.DeserializeObject<Item[]>(sr.ReadToEnd());

just replace the second sr.ReadToEnd() with text and it should work:

var array = JsonConvert.DeserializeObject<Item[]>(text);

Also, as correctly pointed out by @Sachin, your json represent an object with a property called Items that is an array or list of Item objects.
Therefore, you should pass through an intermediate class as shown in @Sachin's answer, or alternatively using a dictionary, like this:

var dict = JsonConvert.DeserializeObject<Dictionary<string,Item[]>>(text);
var array = dict["Items"];

edited Oct 7, 2013 at 12:51

answered Oct 7, 2013 at 11:21

digEmAll

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1 Comment

r3plica Over a year ago

Yeah, works perfectly and I prefer your method over @Sachin simply because I don't like creating wrapper classes :o

Sachin · Accepted Answer · 2013-10-07 11:38:19Z

2

You json string represents the serialization of an object which has a List<Item> as its property. That means you need to deserialize this string into such an object which has List<Item> as a property. So you can make a wrapper class like this

public class Wrapper
{
    public List<Item> items { get; set; }
}

and then Deserialize it like this

var array = JsonConvert.DeserializeObject<Wrapper>(text);

Now you can see your array has two elements inside it ie. array.Count=2

edited Oct 7, 2013 at 11:38

answered Oct 7, 2013 at 11:19

Sachin

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