Collection and Apex Trigger Overview

Data types in Apex

Premitive Datatype: Integer, String, Decimal, Long, Date, DateTime, ID etc.

Sobject Datatype: Salseforce support two types of objects: Standard and Custom. We can define these datatype in this way:

Account objAcc = new Account();//Standard sObject Example

JobInfo__c objJobInfo = new JobInfo__c();// Custom sObject Example

Data Collection

List: List is an ordered collection of elements. Every list have specific data type and we can add same datatype elements in the list in ordered pattern. List can contain duplicate elements.

Syntax:

List<String> lstItem = new List<string>();

Set:  Set is an unordered collection of elements and it cannot have duplicate elements.

Set<string> setItem =  new set<string>();

Map: Map is having two attributes: key and value. Every specific key is mapped with a specific value.

Syntax:

Map<integer,string> mapEmpIDwithEmail = new map<integer,string>();

Put elements in map:

mapEmpIDwithEmail.put(100,’abc@gmail.com’);

mapEmpIDwithEmail.put(101,’xyz@gmail.com’)

Retrieve value from map:

mapEmpIDwithEmail.get(100);    Output: ‘abc@gmail.com’

Apex Trigger Overview

Trigger basically have some piece of apex code which execute on a specific event. Its self executable code and we don’t need to execute that explicitly. It executed implicitly on a specific event.

Syntax:

Trigger <triggername> on <object Name>(trigger Events){

          //Add Trigger logic

}

Types of Triggers:

1.   Before Trigger: Before triggers are used to perform the logic on the same object and specifically we cannot use the DML operation (Insert, update, delete) on these triggers.
These triggers are fired before the data is saved into the database.

2.   After Trigger: After triggers are used to perform the logic on the related objects and these triggers are used to access the fields values that are created by system (Ex: CreatedBy, LasteModifiedBy , Record Id etc..).

Trigger Context Variable:

A.   Trigger.isExecuting:

Returns true if the current context for the Apex code is a trigger, not a Visualforce page, a Web service, or an executeanonymous() API call.

B.   Trigger.isInsert:

Returns true if this trigger was fired due to an insert operation, from the Salesforce user interface, Apex, or the API.

C.   Trigger.isUpdate:

Returns true if this trigger was fired due to an update operation, from the Salesforce user interface, Apex, or the API.

D.   Trigger.isDelete:

Returns true if this trigger was fired due to a delete operation, from the Salesforce user interface, Apex, or the API.

E.   Trigger.isBefore:

Returns true if this trigger was fired before any record was saved.

F.   Trigger.isAfter:

 Returns true if this trigger was fired after all records were saved.

G.   Trigger.isUndelete:

Returns true if this trigger was fired after a record is recovered from the Recycle Bin (that is, after an undelete operation from the Salesforce user interface, Apex, or the API.)

H.  Trigger.New: 

Returns a list of the new versions of the sObject records.Note that this sObject list is only available in insert and update triggers, and the records can only be modified in before triggers.

9. Trigger.newMap:

A map of IDs to the new versions of the sObject records.Note that this map is only available in before update, after insert, and after update triggers.

10. Trigger.Old:

Returns a list of the old versions of the sObject records.Note that this sObject list is only available in update and delete triggers.

11. Trigger.OldMap:

A map of IDs to the old versions of the sObject records.Note that this map is only available in update and delete triggers. 

12. Size:

The total number of records in a trigger invocation, both old and new.

Trigger.New and Trigger.Old Usage:

Below is the table which indicates what are the events which we can use in New and Old triggers.

Trigger Event	Trigger.New, TriggerMap	Trigger.Old, Trigger.oldMap
Before Insert	Yes	No
Before Update	Yes	Yes
Before Delete	No	Yes
Before UnDelete	No	Yes
After Insert	Yes	No
After Update	Yes	Yes
After Delete	No	Yes