Triggers Introduction

Triggers:-

• Apex can be in invoked through the use of triggers.

• A Trigger are functional actions which gets fired on particular events.

That is Data can flow into Data.com at any time. Triggers will happen before records entering into the database and while going out of the database. Note:-        Each event is the firing Point. *onclick *Submit * A Trigger is Apex code that execute before or after the following types of operations.

• Insert
• Update *Delete
• Undelete

We can have a trigger run before an Object's records are inserted into the database, after records have been deleted, or even after a record is restored from the Recycle BIN. * Triggers can be divided into two types.

• Before triggers can be used to update or validate record values before they are saved to the DataBase.
• After triggers can be used to access field values that are set by the database, and to affect changes in other records.

Events:-  Each event is the firing point events are formation of

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Note:- *Before insert Trigger are used mainly for validation rules. Before insert àData screening --->Data Insert *After insert triggers are used mainly for WorkFlow Rules.

Trigger Syntax:-

To define a Trigger, use the following syntax

Trigger TriggerName on ObjectName(trigger-events) {
Code Block;
}

Where trigger-events can be comma- separated list of one or more of the following events.

• Before Insert
• After insert
• After Update
• Before Update
• Before delete
• After Delete
• After Undelete

EX:-  The following code defines a trigger for the before insert and before update events on the Account object.

Trigger Account _Trigger on Account (before insert, Before Update) {
------
-----
}

All triggers define implicit variables that allow developers to access run time context. These variables are contained in the system.Trigger class.

• Trigger.New:- Trigger.new returns a list of the new records of the Sobjects which we are going to insert into the database. 
   This SObject list is only available in insert and Update triggers, and the records can only be modified in before triggers.
• Trigger.old:- Trigger.old returns a list of old records of the Sobjects from the database. Note
  :- This Sobject list is only available in update and delete triggers.
• Trigger.NewMap:- Trigger newMap returns a map of IDs to the new records of the Sobjects.
  Note:- This map is only available in before update, After insert, and after update triggers.
• Trigger.OldMap:- Trigger.OldMap returns a map of ids to the old records of the SObjects.
• Trigger.isAfter:- Trigger.isAfter context variable return true if this trigger was fired after all the records we saved.
• Trigger.isBefore:- This context variable returns true if trigger was fired before any record was saved.
• Trigger.is Insert:- This context variable returns true if the trigger was fired due to an insert operation.
• Trigger .is Update:- This context variable returns true if the trigger was fired due to an update operation.
• Trigger .is Delete: - This context variable returns true if trigger was fired due to a delete operation.
• Trigger is Undelete:- This context variable returns true if trigger was fired ofte a record is recovered from the recycle bin

Note:-Trigger are object specific

 Context variable Consideration:-

• Trigger.new and trigger.old cannot be used in apex DML operations.
• We can use on object to change its own field values using trigger.new, but only in before triggers. In all after triggers, triggers.new is not saved so runtime exception is thrown.
• Trigger.old is always read-only. · We can not delete trigger.new.
• Before insert ==> Trigger.new allowed.
• In after insert triggers ==> Trigger.new not allowed.
• Trigger.new is not available in before delete triggers.
• Trigger.old is not available after undelete triggers.

Bulk Triggers:-

All triggers are bulk triggers by default and can process multiple records at a time. We should always plan on processing, more than one record at a time. When we are uploading bulk records using the data loader, then also triggers will fire for all records at a time.

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