Let me clarify, it supports it. It's just very painful in implementation... On 10/7/08, Ayende Rahien <[EMAIL PROTECTED]> wrote: > Greg, > IInterceptor.Instansiate ? > > On Tue, Oct 7, 2008 at 10:06 PM, Greg Young <[EMAIL PROTECTED]> wrote: > >> >> PI has always been defined as the domain not having any changes in >> specific for it persistence mechanism. >> >> I believe we can give credit to Jimmy Nilsson for creating in the term >> in ADDDP (Applying Domain Driven Design and Patterns). >> >> >> >> You could use nhibernate in a more classic repository implementation >> (DAO layer) and not run into these issue with your proxies. >> >> >> There are many other issues with nhibernate and PI ... my personal >> largest one is the lack of support for constructor mapping which can >> really screw with validation stories but again I can work around this >> in the same way I can with EF, I can use DAOs and put a repository >> over the top of them. >> >> Cheers, >> >> Greg >> >> On Tue, Oct 7, 2008 at 12:55 PM, MAMMON <[EMAIL PROTECTED]> wrote: >> > >> > Lately I've been thinking about Persistence Ignorance. In the past, I >> > don't know if I ever procured a formal definition of the term. It >> > always seemed to make sense in the context it was used. My contextual >> > definition has historically been something like "The UI layer >> > shouldn't have to know or care what OR/M or other technology I'm using >> > to store and retrieve data", a la Separation of Concerns. I shouldn't >> > have any "using" directives for NHibernate namespaces in ANY of my UI >> > code. >> > >> > With a lot of Entity Framework buzz being generated recently, due to >> > it's v1 release with VS2008 SP1, the term Persistence Ignorance has >> > been climbing the Google ranks ladder. Indeed, a Google search of the >> > term shows that of the top 5 results, 3 are about the Entity >> > Framework. Since I work in an otherwise all Microsoft shop, I am very >> > interested in the EF, and the recent buzz has caused me to think more >> > about Persistence Ignorance. Out of the box, EF doesn't have it, but >> > someone at MS has created a PI POCO adapter for EF v1. >> > >> > >> http://blogs.msdn.com/jkowalski/archive/2008/09/09/persistence-ignorance-poco-adapter-for-entity-framework-v1.aspx >> > >> > That article made me think of PI in a new way: not only should the UI >> > layer, or any other consuming layer, not have to know or care what OR/ >> > M or other technology I'm using, but my classes should be able to be >> > POCOs, and I shouldn't have to make them jump through hoops in order >> > to be functional and "persistable". EF v1 (without the mentioned POCO >> > adapter) requires that classes are derived from EntityObject. >> > NHibernate is nice because there is no such requirement. However, I'm >> > not sure NHibernate is really Persistent Ignorant. It might not force >> > me to use dependent base classes, causing tight coupling, but it DOES: >> > + Force me to make all of my methods and properties virtual, for the >> > use of proxies >> > + Force me to override Equals() and GetHashCode(), because of proxies >> > + Prevent me from putting logic in public property getters/setters, >> > because the proxies, upon hydrating objects, would incorrectly execute >> > that logic. >> > + Create the "polymorphic databinding" problem with lists and >> > collections of objects, because of proxies. >> > >> > What specifically got me on this train of thought was this problem: >> > >> > public class Person >> > { >> > private string _fname; >> > private DateTime _dateLastModified; >> > >> > public virtual string FName >> > { >> > get { return _fname; } >> > set >> > { >> > _dateLastModified = DateTime.Now; // Problem here >> > _fname = value; >> > } >> > } >> > } >> > >> > With business rules inlined in the logic in the FName setter, won't >> > lazy loaded instances of Person call the setter to lazily hydrate the >> > instance? And wouldn't that cause the _dateLastModified value to >> > change, even though no real modification has been made? >> > >> > So does NH really achieve Persistence Ignorance? >> > >> > (PS, I'm not trying to be negative here, so let's not get the flame >> > throwers out just yet) >> > > >> > >> >> >> >> -- >> It is the mark of an educated mind to be able to entertain a thought >> without accepting it. >> >> > >> > > > >
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