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protected constructors(?) and group loading

I have a class that I don't want anyone to just be able to instantiate.  They should be forced to use a factory if they want an instance of one.(because, if you do create a new one, and it [as in an entity] already exists in the factory's repository, there will be big problems).  BUT, i also want to be able to load them all at once. Which means, I can't just have my usual method in my DataAccess class that loops through a ResultSet, creates a new Object, and puts it into teh factory's ArrayList or whatnot.  So, what should I do?  Is it worth having to load each object individually for the sake of "proper" design and security?  Or should I say screw it, allow for public constructors and hope no one uses the class wrong?  Is there a magic design pattern that will solve my problem? thanks for advice in advance.
Vince
Wednesday, September 08, 2004
 
 
Loading and creating are different in the way they handle identity: loading assumes and existing object identity, creation needs to generate a new id. I'll just assume loading.

Why not have 2 factory methods? One for single instance loading, the other for bulk loading. Constructor can be private.

static public Object load(final Identity id);
static public Object[] load(final Identity[] ids);
static public Object[] load(final String criteria);

Or

Superclass (since your constructors are only protected) and provide concrete creation logic. Provide to methods load single and multiple.

interface ClassFactory {
public Object load(final Identity id);
public Object[] load(final Identity[] ids);
public Object[] load(final String criteria);
}

class MyFactory implements ClassFactory {
...
}

class Client {
void foo(final ClassFactory cf) {
  try {
      MyObject = cf.load(MyObject.id("000"));
  } catch (ClassCastException cce) {
      // wrong class factory; handle the exception;
  }
}
Dino
Wednesday, September 08, 2004
 
 

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