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2024-02-12T09:56:57Z

Example

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'''Single table inheritance''' is a way to emulate [[object-oriented]] [[inheritance (object-oriented programming)|inheritance]] in a [[relational database]]. When [[Map (mathematics)|mapping]] from a [[database]] table to an object in an [[object-oriented language]], a field in the database identifies what class in the [[hierarchy]] the object belongs to.<ref>{{cite book |last=Fowler |first=Martin |authorlink=Martin Fowler (software engineer) |others=Contributions by Dave Rice, Matthew Foemmel, Edward Hieatt, Robert Mee, and Randy Stafford |date=2003 |title=Patterns of Enterprise Application Architecture |series=The Addison-Wesley Signature Series |publisher=Addison-Wesley |isbn=0-321-12742-0 |page=278}}</ref> All fields of all the classes are stored in the same table, hence the name "Single Table Inheritance". In [[Ruby on Rails]] the field in the table called 'type' identifies the name of the [[class (computer science)|class]]. In [[Hibernate (Java)]] and [[Entity Framework]] this pattern is called Table-Per-Class-Hierarchy and Table-Per-Hierarchy (TPH) respectively.,<ref>{{cite web |date=January 21, 2019 |title=Tutorial: Implement Inheritance with EF in an ASP.NET MVC 5 app |url=http://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-application |accessdate=November 3, 2015}}</ref><ref>{{cite web |last1=King |first1=Gavin |last2=Bauer |first2=Christian |last3=Andersen |first3=Max Rydahl |last4=Bernard |first4=Emmanuel |last5=Ebersole |first5=Steve |others=Graphics design by James Cobb and Cheyenne Weaver |date=September 15, 2010 |title=Chapter 9. Inheritance mapping |edition=Version 3.5.6-Final |work=HIBERNATE - Relational Persistence for Idiomatic Java |url=https://docs.jboss.org/hibernate/orm/3.5/reference/en/html/inheritance.html |accessdate=November 3, 2015}}</ref> and the column containing the class name is called the Discriminator column.

== Example ==
{| class="wikitable"
|+ Blogs
|-
! BlogId !! Discriminator !! Url !! RssUrl
|-
| 1 || Blog || <nowiki>https://blogs.example.com/pets</nowiki> || {{Null result}}
|-
| 2 || RssBlog || <nowiki>https://blogs.example.com/cars</nowiki> || <nowiki>https://blogs.example.com/cars.rss</nowiki>
|}

The table have the <code>Url</code> which is used by all blogs but only blogs of type RssBlog have a value assigned in the <code>RssUrl</code> column, other rows have <code>NULL</code>.

==See also==
* [[Object–relational mapping]]
* [[ActiveRecord (Rails)]]

==References==
{{Reflist}}

==External links==
* [http://www.martinfowler.com/eaaCatalog/singleTableInheritance.html Single Table Inheritance]
* [http://www.yiiframework.com/wiki/198/single-table-inheritance/ Single Table Inheritance in Yii]
* [https://github.com/craigds/django-typed-models Single Table Inheritance in Django]

[[Category:Database theory]]

{{software-eng-stub}}

Single Table Inheritance - Revision history

imported>Frap: /* Example */