DevForce Community Forum : Table Inheritance

Table Inheritance : Kim - Thank you! I'll see...

Mon, 20 Sep 2010 15:46:35 -700

Author: mikewishart
Subject: 2154
Posted: 20-Sep-2010 at 3:46pm

Kim - Thank you! I'll see if we go that route.

Markus,

As I understand it, this is what you're looking for in EDMX.

Your physical database needs a table between Student and Class and needs to look like this.

Once I built the data schema then imported all 5 tables into the EDMX, it worked just fine. Of course I had to delete the FK relationships between Person-Teacher and Person-Student and delete the PersonId on Student and Teacher.

Edited by mikewishart - 20-Sep-2010 at 3:57pm

Table Inheritance : I am trying to do the following...

Mon, 20 Sep 2010 06:36:15 -700

Author: mseeli
Subject: 2154
Posted: 20-Sep-2010 at 6:36am

I am trying to do the following using inheritance (table by hierarchy):

I have a Person and derived from that two Subclasses: Student and Teacher

Now I have a further class called Class with an association between Student and Class (i.e. a Student belongs to a Class, a Class has many Students in it but a Teacher is not in a Class.

So the navigational property from StudentToClass should be on the Student but not on Person or Teacher.

I have tried for hours to get the mapping to work but I could not get it to work.

Is what I am trying possible or does DefForce not support what I am trying to achieve?

Markus Seeli

Table Inheritance : I don't have a good answer...

Tue, 14 Sep 2010 19:31:17 -700

Author: kimj
Subject: 2154
Posted: 14-Sep-2010 at 7:31pm

I don't have a good answer for the LastUpdateTime columns. That might be a good question for the EF forum on MSDN (I'm really not trying to dodge the question, but best to ask the experts) - http://social.msdn.microsoft.com/Forums/en-US/adodotnetentityframework/threads/

You shouldn't have a problem with an ExecuteSave override, unless you're really trying to take control of the save process, which you shouldn't. You'll be able to retrieve entities OfType or OfType and work with them as you normally would. The one thing that can sometimes be confusing when working with inherited entities is that the EntityQuery auto-generated on your EntityManager will return entities of the type and all base types, so entityManager.Persons will return any type of person.

Table Inheritance : Thanks! We're looking at...

Tue, 14 Sep 2010 17:16:49 -700

Author: mikewishart
Subject: 2154
Posted: 14-Sep-2010 at 5:16pm

Thanks! We're looking at a Table-per-Type architecture here.

Kim, your second link was extremely helpful and almost got it. I was missing the step of deleting the primary key columns from the mapping on the inherited tables.

One more item to stump me. If we have a common column between the two tables, say something we use for replication (eg. LastUpdateTime), it can certainly be the same value in both tables, but I don't see any way to map the property mapping in the descendant table to the parent table. I suppose I can rename it (LastUpdateTimeTPT) and set it to the same value and change its setter/getter to private, but that's not the most perfect solution. If that's what I need to do, then I'll look at that.

Looking ahead a bit. When I get to the EntityServerSaveInterceptor.ExecuteSave(), should I be concerned about anything. Any pitfalls here?

Thanks again!
Mike

Table Inheritance : We don't currently have any...

Tue, 14 Sep 2010 16:12:42 -700

Author: kimj
Subject: 2154
Posted: 14-Sep-2010 at 4:12pm

We don't currently have any samples in the DevForce Resource Center showing inheritance, but we should have some samples lying around which we can send you. The BaseType isn't new, since inheritance was supported in EF v1, and by extension DevForce. We support everything EF does regarding the three "flavors" of inheritance based on your DB schema: Table per Type (TPT), Table per Hierarchy (TPH) and Table per Concrete type (TPC). These all expect the PK to be the same, so I'm not sure if you're running into a problem or just working through the design conceptually.

I'm trying to find a good inheritance write up from Microsoft and not seeing much, but here are a few links to provide an overview:

http://blogs.msdn.com/b/alexj/archive/2009/04/15/tip-12-choosing-an-inheritance-strategy.aspx?CommentPosted=true

http://www.robbagby.com/entity-framework/entity-framework-modeling-table-per-type-inheritance/

http://www.robbagby.com/entity-framework/entity-framework-modeling-table-per-hierarchy-inheritance/

If you'd like a sample showing a specific flavor of inheritance just let us know.

Table Inheritance : My other suggestion is to look...

Tue, 14 Sep 2010 12:46:49 -700

Author: DenisK
Subject: 2154
Posted: 14-Sep-2010 at 12:46pm

My other suggestion is to look at our PropertyInterceptors and see if it can help you do what you're trying to achieve.

PropertyInterceptors are "is intended to replace, and expand upon, the technique of marking properties as virtual and overriding them in a subclass".

http://drc.ideablade.com/xwiki/bin/view/Documentation/UsingPropertyInterceptors

Table Inheritance : Hi Mike;Overriding a property...

Tue, 14 Sep 2010 11:58:40 -700

Author: DenisK
Subject: 2154
Posted: 14-Sep-2010 at 11:58am

Hi Mike;

Overriding a property of a generated DevForce entity via standard code generation is not possible. You might be able to do it by implementing a custom .tt template but other DevForce features might break.

Table Inheritance : Is there an example of how to...

Mon, 13 Sep 2010 14:37:18 -700

Author: mikewishart
Subject: 2154
Posted: 13-Sep-2010 at 2:37pm

Is there an example of how to use the (new?) "Base Type" property for an entity?

We're trying to do something along the lines of:

Person
(pk)PersonId
Name
Address
City

Employee -> Person
(pk)PersonId
StartDate
Status

I can't see how to get around the Employee having the same primary key as the Person if you set Person as the base type for Employee. The Employee table requires the field for the relationship to work.

Thanks!