How to make parallel async queries in EF Core 3.0 with repository pattern?

Question

I have repository like

public interface IEmployeeRepository
{
  Task<EmployeeSettings> GetEmployeeSettings(int employeeId);
  Task<ICollection<DepartmentWorkPosition>> GetWorkPositions(int employeeId);
}

Constructor of repository (DbContext injection):

public EmployeeRepository(EmployeeDbContext dbContext)
{
  _dbContext = dbContext;
}

And call it in EF Core 2.0 like

var settingsTask = _employeeRepository
    .GetEmployeeSettings(employeeId.Value);

var workPositionsTask = _employeeRepository
    .GetWorkPositions(employeeId.Value);

await Task.WhenAll(settingsTask, workPositionsTask);

// do other things...

Problem:

With EF Core 3.0 there is InvalidOperationException: a second operation started on this context before a previous operation completed...

DbContext is registered in ConfigureServices like

services.AddDbContext<EmployeeDbContext>(ServiceLifetime.Transient);

Tutorial says following: Entity Framework Core does not support multiple parallel operations being run on the same DbContext instance.

But! How to use it with repositories in async?

Answer 1

How to use it with repositories in async?

You can only have one simultaneous asynchronous request per repository. If you need to have more than one at a time, then you need more than one repository. This may require you to inject a repository factory into your types.