2 - Configuring Commands

Unlike many UI applications, Console or Command Line applications have limitations to user interactions. For example, console applications typically read text commands during a while loop as a standard design pattern. This section will outline the command line design and set up the loop to allow the user to give continual commands.

2.1 Designing the Commands

Our Tasks Console app will have five commands that map to Ditto and general console commands. We will need:

1. --insert to allow the user to .insert a new document into the ditto.collection('tasks") collection
2. --toggle to allow the user to .update a new document's bool isCompleted property by its _id
3. --delete to allow the user to .remove a new document by its _id
4. --list will print every current Task that we have in the collection. In addition, we will always call this method before every item.
5. --exit will quit the console app.

As a best practice, long-running console applications should continuously print the primary set of commands as long as they are succinct. We'll create a utility method called ListCommands() which, will Console.WriteLine each of the commands.

Program.cs

using System;using DittoSDK;using System.Collections.Generic;
namespace Tasks{    class Program    {
      public static void Main(params string[] args)      {        ditto = new Ditto(DittoIdentity.OnlinePlayground("REPLACE_ME_WITH_YOUR_APP_ID", "REPLACE_ME_WITH_YOUR_PLAYGROUND_TOKEN"), path);
        // ... omitted for brevity        // see `setup`      }
      public static void ListCommands()      {          Console.WriteLine("************* Commands *************");          Console.WriteLine("--insert my new task");          Console.WriteLine("   Inserts a task");          Console.WriteLine("   Example: \"--insert Get Milk\"");          Console.WriteLine("--toggle myTaskTd");          Console.WriteLine("   Toggles the isComplete property to the opposite value");          Console.WriteLine("   Example: \"--toggle 1234abc\"");          Console.WriteLine("--delete myTaskTd");          Console.WriteLine("   Deletes a task");          Console.WriteLine("   Example: \"--delete 1234abc\"");          Console.WriteLine("--list");          Console.WriteLine("   List the current tasks");          Console.WriteLine("--exit");          Console.WriteLine("   Exits the program");          Console.WriteLine("************* Commands *************");      }    }}

2.2 Observing the Tasks with a Live Query

As we insert, update, and delete our tasks, we will update the Tasks collection. To sync changes coming from other devices, we will need create a Live Query by calling .Observe. Remember Ditto will only sync with devices by calling .Observe on queries. The .Observe method will return a DittoLiveQuery object. As long as the DittoLiveQuery object stays in scope and is not garbage collected, the Live Query will fire for any changes to the tasks collection. Remember, the .Observe callback will fire for both local changes and remote changes.

DittoLiveQuery liveQuery = ditto.Store["tasks"].Find("!isDeleted").ObserveLocal((docs, _event) => {  // this will fire for all changes synchronized to the store.});

In the context of our console application, we need to:

1. Store a List<Task> as a static variable so that we can print it upon command
2. .Observe all the document in the tasks collection. Take care to store the DittoLiveQuery as a static variable as well.
3. In the .Observe callback, convert all the List<DittoDocument> docs into List<Task> and assign them to both variables detailed in step 1 and 2.

Program.cs

using System;using DittoSDK;using System.Collections.Generic;
namespace Tasks{    class Program    {        static Ditto ditto;
        // 1.        static List<Task> tasks = new List<Task>();        // 2.        static DittoLiveQuery liveQuery;        static DittoSubscription subscription;

        public static void Main(params string[] args)        {            ditto = new Ditto(DittoIdentity.OnlinePlayground("REPLACE_ME_WITH_YOUR_APP_ID", "REPLACE_ME_WITH_YOUR_PLAYGROUND_TOKEN"), path);
            try            {                ditto.StartSync();            }            catch (DittoException ex)            {                Console.WriteLine("There was an error starting Ditto.");                Console.WriteLine("Here's the following error");                Console.WriteLine(ex.ToString());                Console.WriteLine("Ditto cannot start sync but don't worry.");                Console.WriteLine("Ditto will still work as a local database.");            }
            Console.WriteLine("Welcome to Ditto's Task App");
            // 3.            subscription = ditto.Store["tasks"].Find("!isDeleted").Subscribe()            liveQuery = ditto.Store["tasks"].Find("!isDeleted").ObserveLocal((docs, _event) => {                tasks = docs.ConvertAll(document => new Task(document));            });        }
        public static void ListCommands() {          // omitted for brevity        }    }}

We have all the basic building blocks for syncing tasks to a locally stored List<Task> variable. In the following section, we will go over how to map the user commands to actual Ditto live query, insert, update and delete methods.