Factory to create different objects of same interface

Question

I have 1 interface:

public interface ISummary
{
   int EventId {get; set;}
}

And many concrete classes that implement this interface:

public class EmployeeSummary : ISummary
{
   public int EventId {get; set;},
   public int TotalUniqueCount {get; set;}
   public int Location {get; set;}
}

public class CarSummary : ISummary
{
   public int EventId {get; set;}
   public int TotalMiles {get; set;}
   public int TotalHours {get; set;}
}

etc....

The only shared property is the EventId. Is there a way to have 1 factory method that creates all of these summary objects? I want 1 entry point which decides which objects to create.

So something like:

public ISummary CreateSummary(ConcreteObjectType with properties)
{
if EmployeeSummary
 --Call this method to create and return EmployeeSummary

if CarSummary
 --Call this method create and return CarSummary
}

I want all calls within other classes to call this method rather than creating the objects themselves.

The part I am struggling with is how do I pass the properties to assign to the objects to this CreateSummary method since all the properties on the objects will be different?

I am open to changing the objects at this point at well if there is a better design pattern I should be using here.

Answer 1

Well, that's exactly why Factory Method pattern exists :

public class SummaryFactory
{        
    // new instance with values assigned by action delegate or default
    public T Create<T>(Action<T> action = null) where T : ISummary, new()
    {
        var result = new T();
        action?.Invoke(result);             
        return result;
    }

    // with object to assign value from (map) 
    public T Create<T>(object map) where T : ISummary, new()
    {
        var result = new T();
        PropertyInfo[] props = map.GetType().GetProperties();
        PropertyInfo[] tProps = typeof(T).GetProperties();

        foreach (var prop in props)
        {
            var upperPropName = prop.Name.ToUpper();
            var foundProperty = tProps.FirstOrDefault(p => p.Name.ToUpper() == upperPropName);
            foundProperty?.SetValue(result, prop.GetValue(map));
        }
        return result;
    }

    // new instance without generic parameters
    public object Create(Type type)
    {
        var instance = Activator.CreateInstance(type);

        // add some other logic that changes instance
        return instance;
    }
}

And now you can use this factory :

var factory = new SummaryFactory();
var carSummary = factory.Create<CarSummary>();
var carSummary2 = factory.Create<CarSummary>(car => { car.TotalMiles = 50; });
var carSummary3 = factory.Create<CarSummary>(new { TotalMiles = 50 });
var employeeSummary = factory.Create(typeof(EmployeeSummary));