CODEWITHSUNDEEP
c#async-await
leapold
leapold

Reputation: 133

Load data (async/await)

I'm not sure about this state. I need to get data from database asynchrony.

I have class DB

public class Db{

public async Task<ObservableCollection<Person>> GetAllPerson()
{ 
 using (var context = new Db())
 {
    // get data and return ObservableCollection<Person>  
 }
}

}

In the ViewModel I call LoadData function.

public class VM{

    public ObservableCollection<Person> Person { get; set; }
private readonly DB sqlRepository;

public VM()
{
    sqlRepository=new DB();
    LoadData();
}
private async void LoadData()
    {
        Person= await sqlRepository.GetAllPerson();
    }

}

I got warning: Warning CS1998 This async method lacks 'await' operators and will run synchronously.

How can I run my function asynchronously? Should I use ?

Person=await Task.Run(()=>this.sqlRepository.GetAllPerson());

Upvotes: 1

Views: 7963

Answers (1)

Stephen Cleary
Stephen Cleary

Reputation: 456322

How can I run my function asynchronously?

You're approaching your problem from the wrong direction. You're trying to go "outside in" - your ViewModel wants to load the database data asynchronously. And that's a fine way of describing the problem, but it's the wrong way to solve it.

To solve it more easily, start at the other end. Whatever methods are actually calling into the database (e.g., Entity Framework calls) should be made asynchronous first, and then let async grow out from there. Eventually you'll end up with something like:

public async Task<ObservableCollection<Person>> GetAllPersonAsync()
{ 
  using (var context = new Db())
  {
    // This code wasn't shown in the question.
    // But from the compiler warning, it was probably using something like
    //   var people = People.ToList();
    //   return new ObservableCollection<Person>(people);
    // And the async version should be:
    var people = await People.ToListAsync();
    return new ObservableCollection<Person>(people);
  }
}

Which you could consume as:

private async void LoadData()
{
  Person = await sqlRepository.GetAllPersonAsync();
}

But I recommend consuming it via NotifyTask as described in my MVVM async data binding article. That approach would give you the ability to data-bind busy spinners and whatnot.

Should I use [Task.Run]?

No. That's "fake asynchrony" - where your code acts like it's asynchronous but it's really just synchronously running on a background thread.

Upvotes: 5

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