A couple of helper functions to store and retrieve objects stored in Tridions application data. Useful for "caching" costly reports generated by the CoreService, but also just storing and retrieving C# objects in application data.

AppDataExamples.cs

/// <summary>
/// Save an object in appData (stored in the CM DB) by serializing the object into a string,
/// then converting it to an array of bytes and storing it via the CoreService client.
/// </summary>
/// <param name="applicationId">The ID which the appData can be retrieved.</param>
/// <param name="data">The object to be stored in appData by applicationId.</param>
public void SaveAppData<T> (string applicationId, T data)
{
    using (var client = new SessionAwareCoreServiceClient(""))
    {
        try
        {
            string serializedData = JsonConvert.SerializeObject(data);

            ApplicationData appData = new ApplicationData()
            {
                ApplicationId = applicationId,
                Data = Encoding.Unicode.GetBytes(serializedData),
                TypeId = "System.String"
            };

            client.SaveApplicationData(Settings.EMPTY_TCM_ID, new ApplicationData[] { appData });
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }
}

/// <summary>
/// Read an object from appData and serialize it. The object is retrieved by applicationId.
/// </summary>
/// <param name="applicationId">The ID to retrieve the object by.</param>
/// <returns>Deserialized object retrieved from appData.</returns>
public T ReadAppData<T>(string applicationId)
{
    T deserializedObject = default(T);

    using (var client = new SessionAwareCoreServiceClient(""))
    {
        try
        {
            var appData = client.ReadApplicationData(Settings.EMPTY_TCM_ID, applicationId);

            if(appData != null)
            {

                var content = Encoding.Unicode.GetString(appData.Data);

                deserializedObject = JsonConvert.DeserializeObject<T>(content);
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

    return deserializedObject;
}