Object-Relational Programming

Introduction to Object-Relational Programming.
http://simono.github.io/scala-orp/

Transcript

1. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Object-Relational Programming Simon Olofsson simon@olofsson.de | @solofs http://simono.github.com/scala-orp/ 14 December 2012
2. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example What is ORP? Object-Relational Programming = OOP + Relationships Objects are useless without Relationships between them There are no high-level abstractions to define Relationships Instance variables and direct References are used
3. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Defining a Relationship - manually class Customer { val c o n t r a c t s = L i s t B u f f e r [ Contract ] ( ) } class Contract ( var domain : Domain ) class Domain ( val name : S t r i n g )
4. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Two Problems with Relationships
5. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example The Representation of Relationships depends on the Multiplicity class Contract { val domains = L i s t B u f f e r [ Domain ] ( ) }
6. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Bidirectional Relations are hard to maintain
7. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example class Contract { val domains = L i s t B u f f e r [ Domain ] ( ) def addDomain (d : Domain ) { d . contract . domains −= d domains + = d d . contract = t h i s } } class Domain ( val name : String , var contract : Contract ) { def setContract ( c : Contract ) { contract . domains −= t h i s c ontract = c c ontract . domains + = t h i s } }
8. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Two Problems with Relationships 1 The Representation of Relationships depends on the Multiplicity 2 Bidirectional Relations are hard to maintain A simple solution 1 Always use Collection semantics 2 Generate the Code to maintain bidirectional Relations
9. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example How do we define Relationships? We don’t define them inline (i. e. in a Class) We define them separately What do we need? A Relationship Two Roles, that belong to a Relationship Classes that can "play" these Roles
10. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example The API Annotation Meaning @relationship Define a Relationship @role Define a Role @plays(role[<Rolename>]) Play a Role @playsFor(role[<Rolename>], Play a Role for another Class classOf[<Classname>])
11. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Defining a Relationship - with ORP @r e l a t i o n s h i p object CustomerContract { @r o l e (One) t r a i t Customer @r o l e t r a i t Contract } @r e l a t i o n s h i p object ContractDomain { @r o l e (One) t r a i t Contract @r o l e t r a i t Domain { val name : S t r i n g } }
12. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example @p l a y s ( r o l e [ CustomerContract . Customer ] ) class Customer @p l a y s ( r o l e [ CustomerContract . Contract ] , r o l e [ ContractDomain . Contract ] ) class Contract @p l a y s ( r o l e [ ContractDomain . Domain ] ) class Domain ( val name : S t r i n g )
13. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example Some Advanced stuff "generic" Relationships additional Methods playsFor
14. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example @r e l a t i o n s h i p object PartWhole { @r o l e t r a i t Part { def belongsTo ( whole : Whole ) = partOf ( whole , t h i s ) } @r o l e (One) t r a i t Whole { def c o n t a i ns ( part : Part ) = partOf ( this , part ) } def partOf ( whole : Whole , part : Part ) = whole . getParts . c o n t a i n s ( part ) }
15. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example @p l a y s ( r o l e [ PartWhole . Part ] ) class Engine @p l a y s ( r o l e [ PartWhole . Whole ] ) class Car
16. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example @playsFor ( r o l e [ PartWhole . Part ] , c l a s s O f [ Car ] ) @playsFor ( r o l e [ PartWhole . Whole ] , c l a s s O f [ Valve ] ) class Engine @playsFor ( r o l e [ PartWhole . Whole ] , c l a s s O f [ Engine ] ) class Car @playsFor ( r o l e [ PartWhole . Part ] , c l a s s O f [ Engine ] ) class Valve ( val brand : S t r i n g )
17. What is ORP? Two Problems with Relationships How do we define Relationships? API Easy example Advanced example val car = new Car () val engine = new Engine () val v a l v e = new Valve ( "Jimma" ) engine . addValve ( v a l v e ) engine . addPart ( v a l v e ) a s s e r t ( v a l v e . belongsTo ( engine )) a s s e r t ( engine . c o n t a i n s ( v a l v e )) car . addPart ( engine ) a s s e r t ( engine . belongsTo ( car )) a s s e r t ( car . c o n t a i n s ( engine )) // Won ’ t work // car . addPart ( v a l v e )