Batch Apex in salesforce | Test class for Batch job | how to schedule batch job

Batch Apex

A Batch class allows you to define a single job that can be broken up into manageable chunks that will be processed separately.

When to use Batch Apex

One example is if you need to make a field update to every Account in your organization. If you have 10,001 Account records in your org, this is impossible without some way of breaking it up. So in the start() method, you define the query you're going to use in this batch context: 'select Id from Account'. Then the execute() method runs, but only receives a relatively short list of records (default 200). Within the execute(), everything runs in its own transactional context, which means almost all of the governor limits only apply to that block. Thus each time execute() is run, you are allowed 150 queries and 50,000 DML rows and so on. When that execute() is complete, a new one is instantiated with the next group of 200 Accounts, with a brand new set of governor limits. Finally the finish() method wraps up any loose ends as necessary, like sending a status email.

Sample Batch Apex

1) Start method is automatically called at the beginning of the apex job. This method will collect record or objects on which the operation should be performed. These record are divided into subtasks & passes those to execute method.

2) Execute Method performs operation which we want to perform on the records fetched from start method.

3) Finish method executes after all batches are processed. Use this method to send confirmation email notifications.

global class AccountUpdateBatchJob implements Database.Batchable<sObject>
{
    global Database.QueryLocator start(Database.BatchableContext BC)
    {
        String query = 'SELECT Id,Name FROM Account';
       
        return Database.getQueryLocator(query);
    }
    global void execute(Database.BatchableContext BC, List<Account> scope)
    {
        for(Account a : scope)
        {
            a.Name = a.Name + 'Updated by Batch job';
        }
        update scope;
    }
    global void finish(Database.BatchableContext BC) {
    }
}

Calling on Batch Apex

            AccountUpdateBatchJob obj = new AccountUpdateBatchJob();
            DataBase.executeBatch(obj);

Scheduler Class For Batch Apex

global class AccountUpdateBatchJobscheduled implements Schedulable 
{
    global void execute(SchedulableContext sc) 
    {
        AccountUpdateBatchJob b = new AccountUpdateBatchJob(); 
        database.executebatch(b);
    }
}

Please check below post for scheduler test class

URL :- http://amitsalesforce.blogspot.in/2017/07/how-to-write-test-class-for-scheduler.html

How to Schedule scheduler class

There are two option we have schedule the scheduler classes.
1) By System Scheduler.
2) By Developer console

System Scheduler.

Step 1) Click on Setup->Apex class. Then search Schedule Apex button.

Step 2) Select the scheduler class and set Time like below screen shot.

By Developer console 

Execute below code from developer console :-

AccountUpdateBatchJobscheduled m = new AccountUpdateBatchJobscheduled();
String sch = '20 30 8 10 2 ?';
String jobID = system.schedule('Merge Job', sch, m);

Test Class

@isTest
public class AccountUpdateBatchJobTest
{
    static testMethod void testMethod1()
    {
        List<Account> lstAccount= new List<Account>();
        for(Integer i=0 ;i <200;i++)
        {
            Account acc = new Account();
            acc.Name ='Name'+i;
            lstLead.add(acc);
        }
       
        insert lstAccount;
       
        Test.startTest();

            AccountUpdateBatchJob obj = new AccountUpdateBatchJob();
            DataBase.executeBatch(obj);
           
        Test.stopTest();
    }
}

Limits in Batch Apex

1) Up to five queued or active batch jobs are allowed for Apex
2) Cursor limits for different Force.com features are tracked separately. For example, you can have 50 Apex query cursors, 50 batch cursors, and 50 Visualforce cursors open at the same time.
3) A maximum of 50 million records can be returned in the Database.QueryLocator object. If more than 50 million records are returned, the batch job is immediately terminated and marked as Failed
4) If the start method returns a QueryLocator, the optional scope parameter of Database.executeBatch can have a maximum value of 2,000. If set to a higher value, Salesforce chunks the records returned by the QueryLocator into smaller batches of up to 2,000 records. If the start method returns an iterable, the scope parameter value has no upper limit; however, if you use a very high number, you may run into other limits.
5) If no size is specified with the optional scope parameter of Database.executeBatch, Salesforce chunks the records returned by the start method into batches of 200, and then passes each batch to the execute method.Apex governor limits are reset for each execution of execute.
6) The start, execute, and finish methods can implement up to 10 callouts each
7) The maximum number of batch executions is 250,000 per 24 hours
8) Only one batch Apex job's start method can run at a time in an organization. Batch jobs that haven’t started yet remain in the queue until they're started. Note that this limit doesn’t cause any batch job to fail and execute methods of batch Apex jobs still run in parallel if more than one job is running

Some Useful link :-

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_batch_interface.htm
https://developer.salesforce.com/docs/atlas.en-us.apex_workbook.meta/apex_workbook/apex_batch_intro.htm

Types of Sharing in Salesforce

1. Force.com Managed Sharing
Force.com managed sharing involves sharing access granted by Force.com based on record ownership, the role hierarchy, and sharing rules:

• 1.1 Record Ownership :- Each record is owned by a user or optionally a queue for custom objects, cases and leads. The record owner is automatically granted Full Access, allowing them to view, edit, transfer, share, and delete the record.

• 1.2 Role Hierarchy :- The role hierarchy enables users above another user in the hierarchy to have the same level of access to records owned by or shared with users below. Consequently, users above a record owner in the role hierarchy are also implicitly granted Full Access to the record, though this behavior can be disabled for specific custom objects. The role hierarchy is not maintained with sharing records. Instead, role hierarchy access is derived at runtime. For more information, see “Controlling Access Using Hierarchies” in the Salesforce online help.

• 1.3 Sharing Rules :-Sharing rules are used by administrators to automatically grant users within a given group or role access to records owned by a specific group of users. Sharing rules cannot be added to a package and cannot be used to support sharing logic for apps installed from Force.com AppExchange. Sharing rules can be based on record ownership or other criteria. You can't use Apex to create criteria-based sharing rules. Also, criteria-based sharing cannot be tested using Apex. All implicit sharing added by Force.com managed sharing cannot be altered directly using the Salesforce user interface, SOAP API, or Apex.

2. User Managed Sharing, also known as Manual Sharing
User managed sharing allows the record owner or any user with Full Access to a record to share the record with a user or group of users. This is generally done by an end-user, for a single record. Only the record owner and users above the owner in the role hierarchy are granted Full Access to the record. It is not possible to grant other users Full Access. Users with the “Modify All” object-level permission for the given object or the “Modify All Data” permission can also manually share a record. User managed sharing is removed when the record owner changes or when the access granted in the sharing does not grant additional access beyond the object's organization-wide sharing default access level.

3. Apex Managed Sharing
Apex managed sharing provides developers with the ability to support an application’s particular sharing requirements programmatically through Apex or the SOAP API. This type of sharing is similar to Force.com managed sharing. Only users with “Modify All Data” permission can add or change Apex managed sharing on a record. Apex managed sharing is maintained across record owner changes.
https://developer.salesforce.com/page/Using_Apex_Managed_Sharing_to_Create_Custom_Record_Sharing_Logic 

trigger Hiring_Manager_Job_Share on Job__c (after insert) {
    if(trigger.isInsert)
 {
  List<Job__Share> jobShares  = new List<Job__Share>();

  for(Job__c job : trigger.new)
  {
   Job__Share hiringManagerShare = new Job__Share();
   hiringManagerShare.ParentId = job.Id;
   hiringManagerShare.UserOrGroupId = job.Hiring_Manager__c;
   hiringManagerShare.AccessLevel = 'edit';
   hiringManagerShare.RowCause = Schema.Job__Share.RowCause.Hiring_Manager_Access__c;
   jobShares.add(hiringManagerShare);
  }
    Database.SaveResult[] jobShareInsertResult = Database.insert(jobShares,false);
    }
}