Interview Questions on Future Method in Salesforce

 You can call a future method for executing long-running operations, such as callouts to external Web services or any operation you would like to run in its own thread, on its own time.
Prevent the mixed DML error.

 Methods with the future annotation must be static methods, and can only return a void type.

global class FutureClass {
    @future
    public static void myFutureMethod() {   
         // Perform some operations
    }
}

1. Methods with the future annotation must be static methods.
2. Can only return a void type.
3. The specified parameters must be primitive data types, arrays of primitive data types, or collections of primitive data types.

Notably, future methods can’t take standard or custom objects as arguments. You can pass the List of record IDs that you want to process asynchronously.

 You can pass primitive data types, arrays of primitive data types, or collections of primitive data types as parameters. No sObjects OR objects as arguments can be passed.

 The reason why sObjects can’t be passed as arguments to future methods is that the sObject might change between the time you call the method and the time it executes. In this case, the future method will get the old sObject values and might overwrite them.

 Future methods are not guaranteed to execute in the same order as they are called. When using future methods, it’s also possible that two future methods could run concurrently, which could result in record locking.

 To call Future methods from Process Builder, call the future method from the invocable method.

 To work with sObjects, pass the sObject ID instead (or collection of IDs) and use the ID to perform a query for the most up-to-date record.

global class FutureMethodRecordProcessing {
    @future
    public static void processRecords(List<ID> recordIds){   
    // Get those records based on the IDs
    List<Account> accts = [SELECT Name FROM Account WHERE Id IN :recordIds];
    // Process records
    }
}

 To allow callout from the future method annotation needs an extra parameter (callout=true) to indicate that callouts are allowed. 

Here is example:

global class FutureMethodExample {
    @future(callout=true)
    public static void getStockQuotes(String acctName){
        // Perform a callout to an external service
    }
}

 You can invoke future methods the same way you invoke any other method.

FutureMethodExample.doCallouts('Account');

 No you can’t, because Calling a future method is not allowed in the Batch Jobs.

 Yes, you can.

 We can call future method in following places: 

• Trigger
• Apex Class
• Schedulable Class

 Since you are in batch context, the trigger runs in the same context too, So as soon as the Account records get updated through the batch process or through any future method, the trigger would throw an exception saying “Future method cannot be called from a future or batch method” as a future method cannot be invoked from future or batch method execution context.

 We can update the trigger logic to leverage the System.isFuture() and System.isBatch() calls so that the future method invocation is not made if the current execution context is future or batch.

trigger AccountTrigger on Account (after insert, after update) {
if(!System.isFuture() && !System.isBatch())
// future call
}

 Calling a future method is not allowed in the Execute method, But a web service can be called. A web service can also call an @future method. So, we can define a web service having a future method invocation and call the web service from the execute method of Batch Job.

 Any number of. There are no restrictions as such.

 This code is an invalid code as a future method can’t invoke another future method.

 Workaround could be calling a web service that has future invocation.

 We can also use future methods to isolate DML operations on different sObject types to prevent the mixed DML error.

 There are 2 kinds of sObjects in salesforce.

1. Non-Setup: Account, opportunity, etc

2. Setup: User, groups, etc

In a single transaction Or execution context, If you are performing DML on both kinds, the system doesn’t allow it and throws an exception called Mixed DML exception, stating that a transaction can not have Mixture of DML operation(Setup and Non-Setup).

 We can shift DML operations of a particular kind in the Future scope. Since both the DML operations are isolated from each other, the transaction doesn’t fail.

For example:

public class MixedDMLFuture {
    public static void useFutureMethod() {
        // First DML operation
        Account acc = new Account(Name='Acme');
        insert acc;
        
        // This next operation (insert a user with a role) 
        // can't be mixed with the previous insert unless 
        // it is within a future method. 
        // Call future method to insert a user with a role.
        Util.insertUserWithRole(
            'learnfrenzy.com', 'Test1', 
            'learnfrenzy.com', 'Test2');        
    }
}

 Salesforce uses a queue-based framework to handle asynchronous processes from such sources as future methods and batch Apex. So, We can check the apex jobs if it has run or not.

But if it in the queue, and resources are not available, It won’t show up on Apex jobs Page, So we can poll AsyncApexJob object to get its status.

However, future methods don’t return an ID, so We can’t trace it directly. We can use another filter such as MethodName, or JobType, to find the required job.

 To test methods defined with the future annotation, call the class containing the method in a startTest(), stopTest() code block. All asynchronous calls made after the startTest method are collected by the system. When stopTest is executed, all asynchronous processes are run synchronously.

@isTest
private class MixedDMLFutureTest {
    @isTest static void test1() {
        User thisUser = [SELECT Id FROM User WHERE Id = :UserInfo.getUserId()];
       // System.runAs() allows mixed DML operations in test context
        System.runAs(thisUser) {
            // startTest/stopTest block to run future method synchronously
            Test.startTest();        
            MixedDMLFuture.useFutureMethod();
            Test.stopTest();
        }
        // The future method will run after Test.stopTest();
     
        // Verify account is inserted
        Account[] accts = [SELECT Id from Account WHERE Name='Acme'];
        System.assertEquals(1, accts.size());
        // Verify user is inserted
        User[] users = [SELECT Id from User where username='mruiz@awcomputing.com'];
        System.assertEquals(1, users.size());
    }
}

 Some of the limitations are :

1. It is not a good option to process large numbers of records.

2. Only primitive data types supported.

3. Tracing a future job is also typical.

4. Can’t call future from batch and future contexts, 1 call from queueable context is allowed.

 You can pass wrapper, but for that, you’ll need to serialize/deserialize that parameter. You can convert the Wrapper to a String which is a primitive.

Once converted into a String you can them pass that string as a parameter to the future method in consideration.

Remember we are working with asynchronous apex they will execute only when the resources are available so if we use the object as a parameter then the system will not hold the current data.

4. Did future method execute in the same order they called? 

The answer is no, as they are not guaranteed to execute in the same order. So, can we call it a limitation? Yes, we can overcome this by using the queueable apex.

5. Will future methods run concurrently which means updating the same record by 2 future methods at a same time from different sources or the same source? 

Yes, and which could result in locking the record. so, need to incredibly careful while dealing with future methods.

6. Do I have to take any special care while writing the test class for future methods?

Yes, you need to enclose the code between start and stop test methods.

7. Can I use future method for bulk transactions? 

The answer will not be likeable, but it is good to avoid future and good to use batch processing.

8. What is the limit on future calls per apex invocation? 

50, additionally there are limits base on the 24-hour time frame.

9. Can we user future method in visual force controller constructors? 

The answer is no.

10. Can I call a future method from another future method? 

No, you cannot call one future method from another future method.

Hopefully, this interview series on Future Method will help to understand Future Method clearly and crack the interview.

All the Best...!!  

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