Getting Errors when trying to Deserialize JSON object from API call in C#. (currency exchange)-CodePudding

My goal is to build an API that can load currency data from

When i run the code below, it returns an errors. I am not sure how to resolve this. Just need to convert this JSON into a C# class without error.

Here's the custom C# object to mapped to JSON obj:

     public class ExchangeRate
    {
        public string Disclaimer { get; set; }
        public string License { get; set; }
        public string Timestamp { get; set; }
        public string Base { get; set; }
        public string Rates { get; set; }
    }

Here is the api call where its returning the error:

public static async Task<List> GetLatest(string url) {

        var client = new HttpClient();
        string results = await client.GetStringAsync(url);
        List<ExchangeRate> ratesList = JsonConvert.DeserializeObject<List<ExchangeRate>>(results);
        return ratesList;
    }

CodePudding user response：

Your C# class model does not match the incoming JSON data structure. Rates is an array of items, but you're treating it like a string in your C# model. Timestamp is a number but you're treating it like a string in your C# model.

public class ExchangeRate
{
    public string Disclaimer { get; set; }
    public string License { get; set; }
    public int Timestamp { get; set; }
    public string Base { get; set; }
    public Dictionary<string, double> Rates { get; set; }
}

CodePudding user response：

The example JSON is not a list, it's a single object, this is specified in the exception message

...because the type requires a JSON array

, otherwise it would have [ ] around it indicating an array (can be deserialized to list). Also, your model is flawed as Rates is not a string, but an object, and Timestamp is not a string but a long for the datetime as ticks. Change your model like so:

public class ExchangeRate
{
    //decorate your properties since the json string uses lowercase
    [JsonProperty("disclaimer")]
    public string Disclaimer { get; set; }
    [JsonProperty("license")]
    public string License { get; set; }
    [JsonProperty("timestamp")]
    public long Timestamp { get; set; }
    [JsonProperty("base")]
    public string Base { get; set; }
    [JsonProperty("rates")]
    public Rates Rates { get; set; }
}

public class Rates 
{
    //create the properties for the Rates class
}

OR make the rates property a Dictionary<string, decimal>, NOTE: this could fail if any key is duplicated.

public class ExchangeRate
{
    //decorate your properties since the json string uses lowercase
    [JsonProperty("disclaimer")]
    public string Disclaimer { get; set; }
    [JsonProperty("license")]
    public string License { get; set; }
    [JsonProperty("timestamp")]
    public long Timestamp { get; set; }
    [JsonProperty("base")]
    public string Base { get; set; }
    [JsonProperty("rates")]
    public Dictionary<string, decimal> Rates { get; set; }
}

Change your code to this:

ExchangeRate rate = JsonConvert.DeserializeObject<ExchangeRate>(results);