02 Modeling

This module goes a bit deeper into modeling.

Reading material

• Slides PDF
• Modeling basics

Exercise 1

In this exercise you will extend the Todo.Core model from module 1 to support categories, and create commands and queries with emphasis on the topics presented in the slides.

Task 1 - Add categories to the data model

1. Open the Todo.Core solution in Visual studio located in the Ex01 folder
2. Add a class named Category with a Name and HashSet<Todo> property
3. Add a HashSet<Category> property to the Todo class
4. Add a Dictionary<string,Category> to the TodoModel class

Task 2 - Implement the following commands

1. SetCategoryCommand - add a todo item to a category, create the category if necessary
2. ClearCategoryCommand - remove a todo item from a category
3. SetCategoriesCommand - set the category associations for a given todo

Task 3 - Test the model using scriptcs

1. Create a todo.csx file in the excercise folder with the following content:

   #r Todo.Core\bin\debug\Todo.Core.dll
   
   using Todo.Core;
   using OrigoDB.Core;
   
   var engine = Engine.LoadOrCreate<TodoModel>();
   
   var haskell = engine.Execute(new AddTodoCommand("Learn Haskell"));
   var cook = engine.Execute(new AddTodoCommand("Lamb Roast on Sunday"));
   var dishes = engine.Execute(new AddTodoCommand("Do the dishes"));
   
   engine.Execute(new SetCategoriesCommand{
      TodoId = haskell,
      Categories = new[]{"work", "play"}
   });
   
   engine.Execute(new SetCategoryCommand(cook,"play"));
   engine.Execute(new SetCategoryCommand(dishes, "work"));

2. Launch the script and remain in the REPL.
3. Have a look at a dump of the model by typing engine.GetModel()

Task 4 - Working with lambda queries

In the scriptcs repl, type lambdas to return the following:

1. Category names
2. Todo item names in alphabetical order
3. Unfinished todo items
4. Overdue todo items

See the Completed folder for example solutions in the file lambdas.csx

Task 5 - Queries and Views

1. In Visual Studio, create the following view class:

   [Serializable]
   public class TodoView
   {
       public readonly int Id;
       public readonly string Title;
       public readonly string[] Categories;
   
       public TodoView(Todo todo)
       {
           Id = todo.Id;
           Title = todo.Title;
           Categories = todo.Categories.Select(c => c.Name).ToArray();
       }
   }

2. Create a query to retrieve todos by id:

    [Serializable]
    public class GetTodoByIdQuery : Query<TodoModel, TodoView>
    {
        public readonly int Id;
   
        public GetTodoByIdQuery(int id)
        {
            Id = id;
        }
   
        public override TodoView Execute(TodoModel model)
        {
            return new TodoView(model.Todos[Id]);
        }
    }

3. Create a query named PagedTodosQuery returning TodoView[] with Skip and Take properties (order by Id).
4. Rewrite one or more of the lambdas from task 4 as queries, try LINQ syntax