在Web API中编写API方法时，如何使用async / await启用异步行为

Question

I have written below ASP.NET API code to return employee data

public async Task<IActionResult> employeegroups()
{
    try
    {
        var employeegroups = _context.EmployeeGroups.Select(p => new EmployeeGroupsEntity()
        {
            id = p.Key,
            name = p.Name
        }).ToList();

        return Ok(employeegroups);
    }
    catch
    {
        return BadRequest();
    }
}

I get this warning:

This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread

So, I tried to add `await':

var employeegroups = await _context.EmployeeGroups.Select(p => new EmployeeGroupsEntity()
{
    id = p.Key,
    name = p.Name
}).ToList();

But I get this warning:

List 'EmployeeGroupsEntity' does not contain a definition for 'GetAwaiter' and no extension method 'GetAwaiter' accepting a first argument of​ type List 'EmployeeGroupsEntity' could be found (are you missing a using directive or an assembly reference?)"

Here is my model:

public class EmployeeGroupsEntity
{
    public Guid id { get; set; }
    public string name { get; set; }
}

Answer 1

When we are working with Task<T> as return type of method in combination with async keyword we should also be using await keyword that will make sure that the calling thread is not blocked and will resume the method lines execution followed after the await . So you should be calling the ToListAsync method with await like:

var employeegroups = await _context.EmployeeGroups.Select(p => new EmployeeGroupsEntity()
        {
            id = p.Key,
            name = p.Name
        }).ToListAsync();