Inheritance Mapping: A Walkthrough Guide for Beginners

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Kim — Thu, 13 Jan 2011 18:04:19 GMT

Hi.

I am running into a problem using Insert stored procedures with TPT inheritance. I am trying to add a new row into an inherited class. When I dont have stored procedures in place, entity framework correctly adds the record to the base class then to the inherited class. However, as soon as I map to stored procedures, Entity Framework gets confused and tries to add the inherited class before the base class, so it results in a foreign key error.

Is there a way to solve this problem so that I can add rows to inherited classes using stored procedures?

Thanks

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Graeme Hall — Thu, 18 Nov 2010 14:58:49 GMT

Hi Pedro

How do you implement TPC? This is the kind of strategy we would like to employ but I don't see a description of how you would model it anywhere. Do you have a sample project you could make available that illustrates how we would generate entity objects and db tables from a conceptual model?

thanks

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Eli.M — Fri, 05 Nov 2010 21:14:26 GMT

@Riguinel Sant'Anna

Realize that using a bit mask (your Kind | 2 = 2) where clause against a table in SQL will result in a table scan even if you index the column.

Alternatively from both of your designs, I'd consider creating an ArtistKind Entity, and add a List<ArtistKind> property to your Artist Entity... EF will generate 3 tables, your artist table, the artistkind table and the relationship table between those 2...

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Riguinel Sant'Anna — Wed, 03 Nov 2010 03:16:48 GMT

Hi Pedro,

Great post, but let me ask you about one different scenario:

Given one table called Artists, that have some properties about artists (like name, minibio, etc) and a byte field that bits are used to determine the kind of artist, with values like:

1 - Singer

2 - Actor

4 - Composer

8 - Musician

16 - Director

Note that the same artist can be just of one kind or pertain to more than one. Let's see an example:

+-------------------------------------------------+

| Table: Artist |

+---------------------------------------+--------+

| Name | Kind |

+---------------------------------------+--------+

| Al Pacino | 2 | (Actor)

+---------------------------------------+--------+

| Mel Gibson | 18 | (Actor and Director)

+---------------------------------------+--------+

| Dave Matthews | 15 | (Actor, Singer, Composer and Musician)

+---------------------------------------+--------+

Now, I'm able to do TPH using updatable views with stored procedures (for CRUD).

I also know that it's not possible (for me at least!) do this using conditional mapping since I can't use an expression with bitwise OR, like "(Kind | 2) = 2" in the condition.

I've thought, altenativelly, that change the table structure by splitting de field Kind, into something like:

+-------------------------------------------------------------------------------------------------------+

| Table: Artist |

+---------------------------------------+-------+---------+----------------+-------------+----------+

+---------------------------------------+-------+---------+----------------+-------------+----------+

| Al Pacino | 1 | 0 | 0 | 0 | 0 |

+---------------------------------------+-------+---------+----------------+-------------+----------+

| Mel Gibson | 1 | 0 | 0 | 0 | 1 |

+---------------------------------------+-------+---------+----------------+-------------+----------+

| Dave Matthews | 1 | 1 | 1 | 1 | 0 |

+---------------------------------------+-------+---------+----------------+-------------+----------+

Could work, but doing this, although I can create TPH using the fields in the conditional mapping, the EF (obviously) gives me an error stating that the derived entities (Actor, Singer, etc) are

being mapped to the same rows in the table Artist.

My question is, are there other ways to do that ?

Thanks in advance.

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Pedro Ardila - MSFT — Thu, 28 Oct 2010 21:40:48 GMT

Thanks Vitor.

I will get someone to have a look at the code sample from Connect.

Cheers,

Pedro

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Vitor Castro — Wed, 27 Oct 2010 22:51:07 GMT

Hi Pedro,

Thanks for your reply, I do have a complete simple solution with an edmx that shows the behavior I'm getting, where can I send you this file?

You can browse to connect.microsoft.com/.../table-per-hierarchy-tph-limitation-in-entity-framework where I posted both the description of the problem and the file I mentioned.

Vítor

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Pedro Ardila - MSFT — Wed, 27 Oct 2010 20:41:35 GMT

KristoferA,

I actually ran into your blog post yesterday while doing some reading. Way cool!

Vitor,

I just tried setting up this inheritance by adding a new Entity called TTBikeC, changing TTBike to abstract, and creating an inheritance relationship between TTBikeC and TTBike. Everything worked fine.

Can you send your EDMX and a description of the errors you are getting? I will make sure we troubleshoot it.

Cheers,

Pedro

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Vitor Castro — Wed, 27 Oct 2010 07:00:12 GMT

Hello Pedo,

About a month ago I posted this same question on Connect but I never got any good feedback on this, maybe you can shed some light into this mather.

I have a scenario where I have a base abstract entity from which two types derive. One of these types is concrete while the other is abstract. From this second abstract type another concrete type is derived leaving me with this structure:

AbsT1

|--- ConcT1

|--- AbsT2

|--- ConcT2

This conceptual model is then mapped to a single table in the storage model (TPH). This table has a column to identify the type of record being stored.

In these mappings, conditions are added to both concrete types to get this column fixed values for each case.

Under this condition I always get mapping errors stating that ConcT1 and ConcT2 are mapped to the same rows in the table which in my oppinion shouldn't happen.

Additionally if I derive ConcT1 from AbsT2 instead, keeping everything else the same, all mapping errors are gone and everything works as expected. Another way of making things 'work' is to make both abstract types concrete instead.

Thanks in advance,

Vítor Castro

re: Inheritance Mapping: A Walkthrough Guide for Beginners

KristoferA — Wed, 27 Oct 2010 02:43:54 GMT

Hi Pedro,

On a semi-related note, I have a tool for EFv4 that makes it easy to switch between TPT/TPH/TPC in model-first scenarios. I blogged about it here: huagati.blogspot.com/.../mixing-inheritance-strategies-in-entity.html

re: Inheritance Mapping: A Walkthrough Guide for Beginners

Pedro Ardila - MSFT — Wed, 27 Oct 2010 01:59:52 GMT

Thank you for reading Paul.

As you point out, ORMs help abstract the data storage from the code. This can mean a number of things for different scenarios depending on the underlying requirements. Some applications are all about performance; other applications need to be fully extensible; others heavily rely on the ability to run ad-hoc queries. A developer should pick an inheritance strategy based on their application's needs.

TPT is best for extensibility scenarios. Let's say we add a "FullSusMountainBike" which inherits from MountainBike. Using TPT, all we have to do is create a new entity and set up the inheritance between MountainBike and FullSusMountainBike. Using TPH, we would have to add a new column to the database, which is more disruptive than adding another table.

TPC is great for accessing a concrete object's data. For instance, if we are only querying for TTBikes, we will get great query performance as all of the data needed for our query is on the same table. This is key if one of your main scenario is the creation of ad-hoc reports.

The example you describe -where FullSusMountainBike inherits from MountainBike- is actually a combination of TPC and TPT. The ending result on the database will be a new table for FullSusMountainBike which points back to MountainBike. The model will be able to handle this strategy just fine. However, be aware that the same performance limitations that apply to my original TPT example will apply here.

Hope that helps,

Pedro Ardila