How to switch repositories from View ASP.NET MVC 6-CodePudding

I have database and xml repositories. How I can from view switch repositories for application? For example, the view has a select:

<select>
    <option value="xml">XML Storage</option>
    <option value="sqldb">SQL Database</option>
</select>

Program.cs

// builder.Services.AddSingleton<ITaskRepository, TaskRepositoryXML>();
// builder.Services.AddSingleton<ICategoryRepository, CategoryRepositoryXML>();

builder.Services.AddSingleton<ITaskRepository, TaskRepositoryDB>();
builder.Services.AddSingleton<ICategoryRepository, CategoryRepositoryDB>();

You may have some ideas? Thank you!

CodePudding user response：

First of all, you should register your services to use them in runtime, even though you want to have an option to select later on the fly.

A straightforward yet lovely approach is to use a simple Factory pattern. I added implementation for your TaskRepository, but you should do the exact implementation for the CategoryRepository:

public interface ITaskRepository
{
    IEnumerable<string> GetTasks();
}

public class XmlTaskRepository : ITaskRepository
{
    public IEnumerable<string> GetTasks() =>
        new[] { "Task1 from xml", "Task2 from xml" };
}

public class SqlTaskRepository : ITaskRepository
{
    public IEnumerable<string> GetTasks() =>
        new[] { "Task1 from sql", "Task2 from sql" };
}

Now you need a Factory which I implemented a simple version of it for your convenience:

public class TaskRepositoryFactory
{
    public ITaskRepository GetTaskRepository(string userSelection) =>
        userSelection.ToLowerInvariant() switch
        {
            "xml" => new XmlTaskRepository(),
            "sql" => new SqlTaskRepository(),
            _ => throw new ArgumentException(nameof(userSelection))
        };
}

Finally, you have to register your Factory, which I suggest using Scope instead of Singletone (Assuming that your persistence layer is based on EF Core)

builder.Services.AddScoped<TaskRepositoryFactory>();

This is all you need to do for DI. However, for illustration purposes, I added a simple page and injected the factory's concrete class, and switched to the preferred service based on QueryString (Its absurd, but I think enough for presenting the usage)

public class IndexModel : PageModel
{
    private readonly TaskRepositoryFactory _factory;

    public IndexModel(TaskRepositoryFactory factory)
    {
        _factory = factory;
    }

    public List<string> TasksData { get; set; } = new();

    public void OnGet([FromQuery] string selection = "")
    {
        if (!string.IsNullOrEmpty(selection))
        {
            var repo = _factory.GetTaskRepository(selection);
            TasksData = repo.GetTasks().ToList();
        }
    }
}

And razor page has a simple iteration as per below:

@page
@model IndexModel

@foreach (var dt in Model.TasksData)
{
    <span>@dt</span><br />
}

We can resolve all dependencies, yet we can decide which TaskRepository would be instantiated via the help of Factory Pattern.