Question

Let’s say I have the following C# class that I want to be immutable. You can only set it by using the parametrized constructor.

public class InsulineInjection
{
    private InsulineInjection()
    {
        // We don't want to enable a default constructor.
    }

    public InsulineInjection(Millilitre millilitre, DateTime dateTime, string remark)
    {
        this.Remark = remark;
        this.DateTime = dateTime;
        this.Millilitre = millilitre;
    }

    public string Remark { get; private set; }
    public DateTime DateTime { get; private set; }
    public Millilitre Millilitre { get; private set; }
}

Now I would like to use an ORM to create this POCO. However, as far as I can see all .NET ORM’s expects properties to be accessible and have a public constructor to be able to create this POCO. So I would have to change my POCO into this:

public class InsulineInjection
{
    public InsulineInjection()
    {
    }

    public InsulineInjection(Millilitre millilitre, DateTime dateTime, string remark)
    {
        this.Remark = remark;
        this.DateTime = dateTime;
        this.Millilitre = millilitre;
    }

    public string Remark { get; set; }
    public DateTime DateTime { get; set; }
    public Millilitre Millilitre { get; set; }
}

This however makes my POCO mutable again. Someone using it could simply change any property afterwards which is not wat I want.

As far as I can see it, I could solve this in two different ways:

1. Write my own data access layer (or modify an orm) to be able to create correct POCO instances using the constructor I created.
2. Create some kind of mapper. Let the ORM create simple DTO objects and use the mapper to convert the DTO objects to my POCO at the appropriate time.

I’m leaning towards solution 2. Does someone have an example on how to do this? Or does someone have a better solution than the ones I describe above?

Answer 1

Many OR/Ms work as long as there is a default constructor and setters (no matter if they are public or not, they just have to exist)

So this wont work (no default constructor):

public class InsulineInjection
{
    public InsulineInjection(Millilitre millilitre, DateTime dateTime, string remark)
    {
        this.Remark = remark;
        this.DateTime = dateTime;
        _millilitre = millilitre;
    }

    public string Remark { get; set; }
    public DateTime DateTime { get; set; }
    public Millilitre Millilitre { get { return _millilitre; } }
}

or this (no setter for the last property)

public class InsulineInjection
{
    public InsulineInjection(Millilitre millilitre, DateTime dateTime, string remark)
    {
        this.Remark = remark;
        this.DateTime = dateTime;
        _millilitre = millilitre;
    }

    public string Remark { get; set; }
    public DateTime DateTime { get; set; }
    public Millilitre Millilitre { get { return _millilitre; } }
}

While this will work:

public class InsulineInjection
{
    protected InsulineInjection()
    {
        // works with many OR/Ms
    }

    public InsulineInjection(Millilitre millilitre, DateTime dateTime, string remark)
    {
        this.Remark = remark;
        this.DateTime = dateTime;
        this.Millilitre = millilitre;
    }

    public string Remark { get; private set; }
    public DateTime DateTime { get; private set; }
    public Millilitre Millilitre { get; private set; }
}