Goal of article is to summarize and keep reminding the theory of apex design patterns here: https://developer.salesforce.com/page/Apex_Design_Patterns. However, we use all of them, but we easily forget what is called what and sometimes to even use it.
Here are a list of design patterns, some of which are standard object-oriented patterns in a Force.com context, and some of which are specific Force.com patterns.
- Singleton – minimizing object instantiation for improved performance and to mitigate impact of governor limits.
Example, use a global static variable, before assigning it to a value check if it has already a value.
- Strategy – defining a family of algorithms, enscapsulating each one and making them interchangeable and selectable at runtime
Covers use of interfaces, Aggregation (Has A) relationship, Method Overloading.
- Decorator – extending the functionality of an sObject in Apex
Use of wrapper classes inside wrapper class and perform required operation when it is get;set; in vf page instead when page is loading. We can say it lazy loading. Used in VF page mostly.
- Facade – simplifying the execution of classes with complex interfaces (e.g. web service callouts)
Maintainability of Apex code by simplifying the execution of one or complex classes with a facade class. For example, just create a simple class where place code to execute methods/functions of a complex class.
- Composite – The Composite design pattern can be used to represent an expression in Apex regardless of expression complexity, whilst mitigating the impact of governor limits that can result from recursions.
Example1: 1 OR (2 AND 3)
Expression expr = new OrComposite();
expr.add(new Variable(‘1’));
Expression expr2 = new AndComposite();
expr.add(expr2);
expr2.add(new Variable(‘2’));
expr2.add(new Variable(‘3’));
Example 2: 1 OR (2 AND 3)
Expression expr = (new OrComposite())
.add(new Variable('1'))
.add((new AndComposite())
.add(new Variable('2'))
.add(new Variable('3'))
)
.set('1',false)
.set('2',true)
.set('3',false);
System.debug(expr.evaluate());
//FALSE OR (TRUE AND FALSE) => FALSE
expr.set('3',true);
System.debug(expr.evaluate());
//FALSE OR (TRUE AND TRUE) => TRUE
- Bulk State Transition – efficiently tracking the change of a field value in a trigger and executing functionality based on this change
Apex trigger best practices – Use controller class & helper classes; pass bulk list in method; perform operation on changes and on bulk record.
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