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programming_books_eng

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{
return await _context.Items
.Where(x => x.IsDone == false)
.ToArrayAsync();
}
}
}
57
Create a new service class
You'll notice the same dependency injection pattern here that you saw in
the MVC basics chapter, except this time it's the ApplicationDbContext
that's getting injected. The ApplicationDbContext is already being added
to the service container in the ConfigureServices method, so it's
available for injection here.
Let's take a closer look at the code of the GetIncompleteItemsAsync
method. First, it uses the Items property of the context to access all the
to-do items in the DbSet :
var items = await _context.Items
Then, the Where method is used to filter only the items that are not
complete:
.Where(x => x.IsDone == false)
The Where method is a feature of C# called LINQ (language integrated
query), which takes inspiration from functional programming and makes
it easy to express database queries in code. Under the hood, Entity
Framework Core translates the Where method into a statement like
SELECT * FROM Items WHERE IsDone = 0 , or an equivalent query document
in a NoSQL database.
Finally, the ToArrayAsync method tells Entity Framework Core to get all
the entities that matched the filter and return them as an array. The
ToArrayAsync method is asynchronous (it returns a Task ), so it must be
await ed to get its value.
To make the method a little shorter, you can remove the intermediate
items variable and just return the result of the query directly (which
does the same thing):
public async Task<TodoItem[]> GetIncompleteItemsAsync()
58
Create a new service class
{
return await _context.Items
.Where(x => x.IsDone == false)
.ToArrayAsync();
}
Update the service container
Because you deleted the FakeTodoItemService class, you'll need to
update the line in ConfigureServices that is wiring up the
ITodoItemService interface:
services.AddScoped<ITodoItemService, TodoItemService>();
AddScoped adds your service to the service container using the scoped
lifecycle. This means that a new instance of the TodoItemService class
will be created during each web request. This is required for service