How to Handle Empty or Null JTokens When Mapping JSON to SQL Parameters in C#?

Checking for Empty or Null JToken in a JObject

Problem:

In a C# application, the following code attempts to loop through a JArray of JObjects and assign values to SQL parameters using the JTokenToSql method. However, if a property in the JObject is empty or null, the JTokenToSql method is not working as expected.

JArray clients = (JArray)clientsParsed["objects"];

foreach (JObject item in clients.Children())
{
    command.Parameters["@MyParameter"].Value = JTokenToSql(item["thisParameter"]);
}

JTokenToSql is defined as:

public static object JTokenToSql(JToken obj)
{
    if (obj.Any())
        return (object)obj;
    else
        return (object)DBNull.Value;
}

Solution:

To check whether a property exists on a JObject, use the square bracket syntax and check if the result is null. If the property exists, a JToken will be returned even if its value is null in the JSON.

JToken token = jObject["param"];
if (token != null)
{
    // the "param" property exists
}

To check if a JToken is non-empty, consider using an extension method like the following:

public static class JsonExtensions
{
    public static bool IsNullOrEmpty(this JToken token)
    {
        return (token == null) ||
               (token.Type == JTokenType.Array && !token.HasValues) ||
               (token.Type == JTokenType.Object && !token.HasValues) ||
               (token.Type == JTokenType.String && token.ToString() == String.Empty) ||
               (token.Type == JTokenType.Null) ||
               (token.Type == JTokenType.Undefined)
    }
}

This method will return true if the token is null, empty, or of the undefined type.

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