CustomerController.cs

[Route("customers")]
public class CustomerController
{
    public CustomerController(DbContext context)
    {
        Context = context;
    }
    
    private DbContext Context { get; }

    [HttpGet("{id}")]
    public async Task<IActionResult> Get(int id, CancellationToken cancellationToken)
    {
        var customer = await Context.Customers.FindAsync(id, cancellationToken);
        
        if (customer == null)
        {
            return new NotFoundResult();
        }
        
        return new ObjectResult(customer);
    }
}

CustomerMapper.cs

public class CustomerMapper : IEntityMapper<Customer>
{
    public object Map(Customer customer, int? version)
    {
        if (version.HasValue)
        {
            switch (version.Value)
            {
                case 2: return new CustomerModelV2(customer);
                case 3: return new CustomerModelV3(customer);
            }
        }

        return new CustomerModelV1(customer);
    }
}

VersioningStrategy.cs

public class VersioningStrategy : IVersioningStrategy
{
    public Task<int?> GetVersion(HttpContext context)
    {
        var accept = context.Request.Headers["Accept"];
        
        // Parse out the version from Accept header. Examples:
        //  - application/json                        -> 1
        //  - application/json; version=1             -> 1
        //  - application/vnd.my-app.v2+json          -> 2
        //  - application/vnd.my-app+json; version=3  -> 3
        
        return Task.FromResult<int?>(2);
    }
}