如何创建一个类的构造函数以返回该类的实例的集合？

Question

My program has the following class definition:

public sealed class Subscriber
{
    private subscription;
    public Subscriber(int id)
    {
        using (DataContext dc = new DataContext())
        {
           this.subscription = dc._GetSubscription(id).SingleOrDefault();                
        }            
    }
}

,where

_GetSubscription() is a sproc which returns a value of type ISingleResult<_GetSubscriptionResult>

Say, I have a list of type List<int> full of 1000 id s and I want to create a collection of subscribers of type List<Subscriber> .

How can I do that without calling the constructor in a loop for 1000 times?

Since I am trying to avoid switching the DataContext on/off so frequently that may stress the database.

TIA.

Answer 1

Write a static factory method which calls a private constructor.

public sealed class Subscriber
{
    // other constructors ...

    // this constructor is not visible from outside.
    private Subscriber(DataContext dc, int id)
    {
       // this line should probably be in another method for reusability.
       this.subscription = dc._GetSubscription(id).SingleOrDefault();                
    }

    public List<Subscriber> CreateSubscribers(IEnumerable<int> ids)
    {
        using (DataContext dc = new DataContext())
        {

           return ids
             .Select(x => new Subscriber(dc, x))
             // create a list to force execution of above constructor
             // while in the using block.
             .ToList();
        }            

    }

}