Custom parameters for azure mobile services

CustomParametersServiceFilter.cs

    /// <summary>
    /// Add custom parameters to each request when applying this filter to a mobile service client.
    /// </summary>
    public class CustomParametersServiceFilter : IServiceFilter
    {
        private IDictionary<string, object> parameters;

        public CustomParametersServiceFilter(IDictionary<string, object> parameters)
        {
            this.parameters = parameters;
        }

        public IAsyncOperation<IServiceFilterResponse> Handle(IServiceFilterRequest request, IServiceFilterContinuation continuation)
        {
            // Get previous uri query
            var uriBuilder = new UriBuilder(request.Uri);
            var oldQuery = (uriBuilder.Query ?? string.Empty).Trim('?');

            // Build new query starting with our custom parameters before old query
            var stringBuilder = new StringBuilder();
            foreach (var parameter in parameters)
            {
                // Currently using ToString on the value, an improvement will be to serialize the object properly
                stringBuilder.AppendFormat("{0}={1}&", parameter.Key, parameter.Value);
            }
            stringBuilder.Append(oldQuery);

            // Apply new query to request uri
            uriBuilder.Query = stringBuilder.ToString().Trim('&');
            request.Uri = uriBuilder.Uri;

            return continuation.Handle(request);
        }
    }

ServiceFilterHelpers.cs

    public static class ServiceFilterHelpers
    {
        public static IMobileServiceTable<T> GetTable<T>(this MobileServiceClient mobileService, object parametersObject)
        {
            if (parametersObject != null)
            {
                // Extract parameters to a dictionary
                Dictionary<string, object> parameters = new Dictionary<string, object>();
                foreach (var property in IntrospectionExtensions.GetTypeInfo(parametersObject.GetType()).DeclaredProperties)
                {
                    string name = property.Name;
                    object value = property.GetValue(parametersObject);

                    parameters[name] = value;
                }

                // Apply custom parameters filter and get the requested table
                return mobileService.WithFilter(new CustomParametersServiceFilter(parameters)).GetTable<T>();
            }

            return mobileService.GetTable<T>();
        }
    }

TestCustomParameters.cs

List<User> allUsers = await App.MobileService.GetTable<User>(new { allUsers = true }).ToListAsync();

User.read.js

function read(query, user, request) {

    // Check for the allUsers custom parameter
    if (request.parameters != null && request.parameters.allUsers == "true")
    {
        // With this custom parameter only return the names of the users
        query.select('name');
    }
    else
    {
        // Without it return the current authenticated user only
        query.where({serviceUserId: user.userId});
    }

    request.execute();