Roll up summary functionality through trigger

public class SampleRollupSummary {
 
    public static void rollupContacts(list<contact> lstOfconts){
        system.debug('==lstOfconts== : '+lstOfconts);
        set<id> accIds = new set<id>();
        list<account> updLstOfAccs = new list<account>();
        list<contact> lstCons = new list<contact>();
     
        for(contact con : lstOfconts){
            accIds.add(con.accountid);
        }
        system.debug('==accIds==:'+accIds);
        list<account> lstAccs = [select id,name,Total_Count__c, (select id from contacts) from account where id in : accIds];
     
        for(account acc : lstAccs){
            system.debug('==acc.contacts.size()=='+acc.contacts.size());
            acc.Total_Count__c = acc.contacts.size();
            updLstOfAccs.add(acc);
        }
        if(updLstOfAccs.size() > 0){
            update updLstOfAccs;
        }     
     
    }
 
}


trigger RollupSummaryTriggerOnAccountObj on contact(after insert, after update, after delete, after undelete) {
    if (trigger.isAfter && (trigger.isInsert || trigger.isUpdate || trigger.isUndelete)) {
        SampleRollupSummary.rollupContacts(trigger.new);
    }
    else if (trigger.isAfter && trigger.isDelete) {
        SampleRollupSummary.rollupContacts(trigger.old);
    }
}

Salesforce Governer Limits

1.DML Governing Limits

we can have only 150 DML statements with in a transaction.

we rectify this type of errors by using bulky operations. put similar operation on the object in list and invoke the DML on the list.

2.SOQL Governing Limits

with in a transaction we can write only 100 SOQL queries.

use
Map<Id,Account> accMap=new map<Id,Account>([select id,Name from Account]);

3.DML rows Limit :

Number of DML rows : 10000

4.SOSL Governing Limits :

Number of SOSL queries : 20

5.Maximum CPU time : 10000
6.Maximum heap size : 6000000
7.Number of callouts : 100
8.Number of Email Invocation : 10
9.Number of future calls : 50
10.Number of queueable jobs added to the queue:50
11.Number of mobile apex push calls :10
12.Number of query rows : 50000

DML statements vs Database class Methods

Apex offers two ways to perform DML operations

1.Using DML statements
2.Database class methods

Difference between the two options that by using the Database class method.

You can specify whether or not to allow for partial record processing if errors are encountered.

you can do so by passing an additional second Boolean parameters.

if you specify FALSE for this parameter and if a record fails,the remainder of DML
operations can still succeed.

 ex : Database.insert(accList,false);

False : partial processing allowed
True  : partial processing not allowed

By default this optional parameter is true,which means that if at least one sObject can't be processed,all remaining sObjects won't and an exception will be thrown for the record that causes a failure.

Order of execution of apex code

1. Before triggers:
     If we update child records in before triggers then parent record automatically update.
2. Validation rules:
 If validation matches the criteria then error will populate in same page.
Runs most system validation steps again, such as verifying that all required fields have a non-null value, and runs any user-defined validation rules. The only system validation that Salesforce does not run a second time (when the request comes from a standard UI edit page) is the enforcement of layout-specific rules.
*Note: Saves the record to the database, but does not commit yet.

3. After Triggers:
4. Assignment Rules:
5. Auto Response Rules:
6. Workflow Rules:
If there are workflow field updates, updates the record again.
7. Escalation Rules:
       If the record contains a roll-up summary field or is part of a cross-object workflow, performs calculations and updates the roll-up summary field in the parent record. Parent record goes through save procedure.
     If the parent record is updated, and a grand-parent record contains a roll-up summary field or is part of a cross-object workflow, performs calculations and updates the roll-up summary field in the parent record. Grand-parent record goes through save procedure.
Executes Criteria Based Sharing evaluation.
Commits all DML operations to the database.

8.Executes post-commit logic, such as sending emails

simple steps:
==============
Order of Events

1. Original record is loaded or new record is initialized
2. Fields values are loaded into sObjects
3. System validations rules are executed:
4. Before triggers are executed
5. System validations rules are run again and custom validation rules are checked.
6. Duplicate rules are executed
7. Record is saved but not committed
8. After triggers are executed
9. Assignment rules are executed
10. Auto-response rules are executed
11. Workflow rules are executed
12. Before triggers,system validation rules and after triggers are executed due to workflow field updates
13. Processes are executed
14. Escalation rules are executed
15. Entitlement rules are executed
16. Rull-up summary fields and cross-object formula fields are updated
17. Updated parent and grand parent records are saved
18. Criteria based sharing rules are evaluated
19. DML operations are committed to the database
20. Post-commit logic is executed

Apex Basics

Apex is a strongly typed,object -oriented programming language that allows developers
to execute flow and transaction control statements on the Force.com platform.

Apex enables developers to add business logic to most system events,including button clicks,
related record updates and visualforce pages.

Data Types :
============
1.primitives
2.sObjects
3.Collections

Apex primitive data types include :

1.Boolean : can only be assigned true,false or null
2.Decimal : A number that includes a decimal points.
3.Double : A 64-bit number that includes a decimal point
4.ID : Any Valid salesforce.com ID
5.Integer : A 32bit number that does not include a decimal point.
6.Long : A 64-bit number that does not include a decimal point.
7.String : Any set of characters surrounded by single quotes.
8.Date : A value that indicates a particular day.
9.DateTime : A value that indicates a particular day and time
10.Time : A value that indicates a particular time.

sObjects :
=============
the term sObject refers to any object that can be stored in the Force.com platform database.

An sObject variable represents a row of data and can only be declared in Apex.

ex :
Contact c= new Contact(FirstName='raj';LastName='kiran';
Email ='test@gmail.com');

Account a =new Account(Name='TCS');
insert a;

Account a1=[select Name from Account
where ID='857598jh'];
a1.Name='new  Name';
update a1;

Collection :
============
collection of primitives or sObjects.

A LIST is an ordered collection.so use
list when you wnat to identify list element
based on INDEX NUMBER.
List can contain duplicates.

List<string> colors =new List<string>('red','purple','green');

List<Account> accts=[select Name,Type from Account
where Industry='Energy'];

List<Contact> email_contacts=
[select FirstName,LastName from Contact where
Email!=Null];

1. Set
2. List
3. Map

A set is a collection of unique,unordered elements.it can contain primitive data types or sObjects.

A set is an unordered collection of primitives or sObjects that do not contain any duplicate elements.so use SET if you want to make sure that your collection should not conatin Duplicates.

ex :
Set<String> s = new Set<String>();
Set<String> s = new Set<String>{'Jon', 'Quinton', 'Reid'};

commonly you'll see developers construct a set of IDs from a query,trigger context,etc.
and the use it as part of WHERE clause in their SOQL query.

ex :

Set<ID> ids = new Set<ID>{'0017000000cBlbwAAC','0017000000cBXCWAA4'};
List<Account> accounts = [Select Name From Account Where Id = :ids];


Map :
=====
A MAP is a collection of key-value pairs where each unique key maps to a single value.
Keys can be any primitive data type,while values can be a primitive,sObject,Collection
types or an Apex Object.

Use a map when you want to quickly find something by a key.Each key must be unique
but you can have duplicate values in your MAP.

Map<Integer, String> m = new Map<Integer, String>{5 => 'Jon', 6 => 'Quinton', 1 => 'Reid'};
Map<ID, Set<String>> m = new Map<ID, Set<String>>();
// creates a map where the key is the ID of the record
Map<Id,Account> aMap = new Map<Id, Account>([Select Id, Name From Account LIMIT 2]);

Triggers in Salesforce

Trigger is piece of code that is executes before and after record is Insert/update/Deleted from the force.com database.

There are two types of Triggers:

1.Before trigger are used to update or validate record values before they're saved to the
database.

2.After triggers are used to access field values that are set by the system and to effect changes in other records.The records that fire the after trigger are read-only.

syntax:
========

trigger triggerName on ObjectName(trigger_events)
{

  //code_block

}

where trigger_events can be a comma-separated list of one or more of the following events :

before insert
before update
before delete
after insert
after update
after delete
after undelete

ex :
========
check email null or not before insert update
record


trigger CheckEmail on contact(before Insert,before update)
{
   for(Contact c:Trigger.new)
   {
     if(c.Email ==Null)
      {
        c.Email.addError('Please insert Emil ID);
      }
   } 
}

Trigger Context Variables :
=====================
All triggers define implicit variables that allow developers to access run-time context.


Trigger.isInsert : Returns true if this trigger was fired due to an insert operation.

Trigger.isUpdate : Returns true if this trigger was fired due to an update operation

Trigger.isDelete : Returns true if this trigger was fired due to delete operation.

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

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

Trigger.isUndelete : Returns true if this trigger was fired after a record is recovered from the
Recycle Bin.

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.

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.

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.

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.

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

Trigger.isExecuting : Returns true if the current apex code is a trigger.


ex :


trigger Opportunity_trigger on Opportunity(before insert,before update){

  for(Opportunity p : Trigger.new)
  {
    if(Trigger.isInsert && p.amount<10000)
      {
       p.addError("amount is less than 10000');
      }
    else if(Trigger.IsUpdate && p.Amount<20000)
         {
           p.addError('Amount is less than 20000');
         }

  }

}

ex :

  public class trigger_class{
    public static void trigger_method(List<Opportunity> oppt){

        Double Total_amount=0;
      for(Opportunity o : Select Amount from opportunity where createddate=Today()
                               and CreatedById= : UserInfo.getUserID()]){
         
           Total_amount=Total_Amount +o.Amount;
       
           }

        for(Opportunity o1 : oppt){
         
           Total_amount=Total_Amount +o1.Amount;
       
              if(Total_amount>100000)
                {
                  01.addError('you have exceeded your daily limit');
                }
            }

    }

  }


trigger t1 on Opportunity(before Insert){
trigger_class.trigger_method(Trigger.new);
}

Transaction Control using Database savepoint and rollback in Apex

SavePoint and Rollback will help us to maintain transaction for DML statement.

suppose you have written multiple lines of DML statements in a try block,if any error
occurs during DML Operations,the operation will be rolled back to the most recent
save point and the entire tranasction will not be aborted.

ex :

savepoint sp=Database.setsavepoint();

try
{
// create account

Account a=new Account();
a.Name='Test';
insert a;

// create contact

Contact c=new contact();
a.accountid=a.id;
insert c;

}
catch(DMLException exc)
{

Database.rollback(sp);

}

In this example, if any error occurs while inserting the Account ‘a’ or Contact ‘c’, then the entire transaction will be rolled back to SavePoint ‘sp’, as specified in the catch section by Database.