AG VLSI Design and Architecture

SFB 501 - Project D1: Application System "Buildings"

PSiGene Pattern Catalog

Intent

This Pattern can be used to follow a relation and call a method on all connected objects. Depending on the relations cardinality different code is generated.

Also Known As

Former Patterns: SingleIndirection (obsolete) , ComplexIndirection (obsolete) , ExtendedComplexIndirection (obsolete) .

Motivation

FollowRelation can be used in every case, when relations schould be traversed and an operation schould be called on all connected objects. For example, to print all connected objects a remote operation print could be called on each connected object. The Pattern can be used to follow several relations with any cardinalities.

Applicability

To use this Pattern, only a target class and the rolenames of the relations that should be followed has to be known.

Structure

Participants

Collaborations

Consequences

Example:

    bind: 'target' to: 'Room'; 
    bind: 'operation' to: 'printAll'; 
    bind: 'remoteOperation' to: 'print';
    bind: 'relation' to: '#(#LeftWalls #controlOfRoom)'.

This example will generate a method printAll which will call a print method on all connected LeftWalls and Controls. The Pattern takes care of the cardinality of the relations. The generated method in Smalltalk might look like this:

"follow all relations."

"1:n relation."
self LeftWalls connections do:
    [   :anObject|
        anObject print
    ].
"1:1 relation."
self controlOfRoom instance notNil ifTrue: 
[ self controlOfRoom instance print ].

Implementation

"follow all relations"
{loop}{optionalParameter}

For each relation one loop macro will be evaluated. These loop macros are replaced by a macro called {doLoop} if the actual relation is of cardinality 1:n and by {dontLoop} for cardinalities 1:1.

"1:1 relation."
self {relation} instance notNil ifTrue: 
    [ self {relation} instance
    {remoteOperation}{optionalParameter} ].

"1:n relation."
    self {relation} connections do:
        [   :anObject|
            anObject {remoteOperation}{optionalParameter}
        ].

If {parameter} is set, {optionalParameter} will be replaced with ': {parameter}', else it is replaced by an empty string.

Related Patterns

FollowRelationAndSum , FollowRelationAndCollectObjects .

PEdit description

Pattern FollowRelation Category indirection
    ObjectType use target
    SingleMethod implement operation
    ComplexRelation use relation
    Expression implement optional remoteOperation
    Expression implement optional parameter
End