c# MVC Entity framework model property of type list containing multiple types

Question

I am currently working on a C# MVC project combined with Entity Framework, where I have a view page (Create page) on which the users will need to fill in the required data. I got a model something like the code below. Where the user has a Boat and can select its properties.

public class Boat {
    public string Name{ get; set; }
}

public class Slowboat : Boat {
    public int Length { get; set; }
    public virtual Engine SpeedSource { get; set; }
}

public class Speedboat : Boat {
    public virtual List<?> SpeedSource { get; set; }
    public int Topspeed {get; set; }
}

public class Engine {
    public string EningeType { get; set; }
    public int Horsepower { get; set; }
    public string Manufacturer { get; set; }
}

public class Sail {
    public int SailCount { get; set; }
    public List<int> SailSizes { get; set; }
    public string Manufacturer { get; set; }
}

Everything goes well, a Speedboat has a couple of sails or an engine. The problem arises when a Speedboat has one or more Engine(s) and Sail.

I tried using List<object> type, but this didn't store my data into my database on posting. A kind of wrapper class like underneath is quick solution but there needs to be a better one in my opinion.

public class SpeedPower {
    public Engine Engine_ { get; set; }
    public Sail Sail_ { get; set; }
}

So my question is: how do you store multiple types into one list?

Thanks for a possible solution.

Edit: so as Thomas Flinkow suggested I can make an interface with some of the mutual properties.

public interface ISpeedSource {
    string Manufacturer { get; set; }
}

public class Speedboat : Boat {
    public virtual List<ISpeedSource> SpeedSource { get; set; }
    public int Topspeed {get; set; }
}

So will the other proprties be saved if I use the interface like this?

It sounds like the conceptual modeling is broken. An Engine and a Sail are not the same thing. So what exactly is a "SpeedSource"? Maybe your boats could have a collection of Engines and a collection of Sails as separate collections? Some boats simply have empty collections of one or the other. Unless you can define a common interface of what a "SpeedSource" is. — David
– David, Commented Apr 20, 2018 at 12:38

Thomas Flinkow · Accepted Answer · 2018-04-20 12:48:20Z

1

You can define all your "speed sources" like this:

public class Engine : ISpeedSource { ... }

public class Sail : ISpeedSource { ... }

with ISpeedSource being a simple (maybe empty, but not necessarily) interface

public interface ISpeedSource { ... }

And then have your Speedboat class like this:

public class Speedboat : Boat 
{
    public virtual List<ISpeedSource> SpeedSource { get; set; }
    public int Topspeed { get; set; }
}

_{You might want to overthink your design as David suggested, because empty interfaces should be avoided.}

edited Apr 20, 2018 at 12:48

answered Apr 20, 2018 at 12:38

Thomas Flinkow

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10 Comments

David Over a year ago

As you state, empty interfaces should be avoided. More specifically in this case, when posting a form from the client, I doubt the model binder would know what to do with an empty interface. If all the model binder knows is that it's a collection of ISpeedSource and an ISpeedSource has no properties, it probably wouldn't store anything useful in that collection.

Kitesaint1309 Over a year ago

@Thomas Flinkow I like the suggestion of the interface because there a a few common properties, so I edited my question. But I also have a common class that has a List that will be of a different size by the type of "speedSource", would it be enough to limit this List size on the front-end of my application?

Thomas Flinkow Over a year ago

@Kitesaint1309 If I understand this correctly, you want the interface to have a List<SpeedSize>? If so, you could just do this: interface { IList<SpeedSource> MyList { get; } if it isn't absolutely necessary to restrict the size.

Kitesaint1309 Over a year ago

@ThomasFlinkow yes something like that, I my case it would be something like interface { IList<string> CrewNames { get; set; } which is dependent on the type of boat (sailboats need more crew then engine boats).

Thomas Flinkow Over a year ago

@Kitesaint1309 alright, that would be perfectly fine and imo should work.

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