Interview questions on triggers In salesforce

1.What is trigger ?
Ans: Trigger is piece of code that is executes before and after a record is Inserted/Updated/Deleted from the force.com database.

2.What are different types of triggers in sfdc?
Ans: 1.Before Triggers-These triggers are fired before the data is saved into the database.
2.After Triggers-These triggers are fired after the data is saved into the database.

3.What are trigger context variables?
Ans:
Trigger.isInsert: Returns true if the trigger was fired due to insert operation.
Trigger.isUpdate: Returns true if the trigger was fired due to update operation.
Trigger.isDelete: Returns true if the trigger was fired due to delete operation.
Trigger.isBefore: Returns true if the trigger was fired before record is saved.
Trigger.isAfter: Returns true if the trigger was fired after record is saved.
Trigger.New: Returns a list of new version of sObject records.
Trigger.Old: Returns a list of old version of sObject records.
Trigger.NewMap: Returns a map of new version of sObject records. (map is stored in the form of map)
Trigger.OldMap: Returns a map of old version of sObject records. (map is stored in the form of map)
Trigger.Size: Returns a integer (total number of records invoked due to trigger invocation for the both old and new)
Trigger.isExecuting: Returns true if the current apex code is a trigger.

4.What is the difference between Trigger.New and Trigger.NewMap?
Ans:
Trigger.New is Returns a list of new version of sObject records but Trigger.NewMap is Returns a map of new version of sObject records.

5.What is the difference between Trigger.New and Trigger.Old?
Ans:
Trigger.New is Returns a list of new version of sObject records and Trigger.Old is Returns a list of old version of sObject records.

6.What is the difference between Trigger.New and Trigger.Old in update triggers?
Ans:

7.Can we call batch apex from the Trigger?
Ans: A batch apex can be called from a class as well as from trigger code.
In your Trigger code something like below :-
// BatchClass is the name of batchclass
BatchClass bh = new BatchClass();
Database.executeBacth(bh);

8.What are the problems you have encountered when calling batch apex from the trigger?
Ans:

9.Can we call the callouts from trigger?
Ans: yes we can. It is same as usual class method calling from trigger. The only difference being the method should always be asynchronous with @future

10.What are the problems you have encountered when calling apex the callouts in trigger?
Ans:

11.What is the recursive trigger?
Ans: Recursion occurs in trigger if your trigger has a same DML statement and the same dml condition is used in trigger firing condition on the same object(on which trigger has been written)

12.What is the bulkifying triggers?
Ans: By default every trigger is a bulk trigger which is used to process the multiple records at a time as a batch. For each batch of 200 records.

13.What is the use of future methods in triggers?
Ans: Using @Future annotation we can convert the Trigger into a Asynchrinous Class and we can use a Callout method.

14.What is the order of executing the trigger apex?
Ans:
1. Executes all before triggers.
2. Validation rules.
3. Executes all after triggers.
4. Executes assignment rules.
5. Executes auto-response rules.
6. Executes workflow rules.
7. If there are workflow field updates, updates the record again.
8. If the record was updated with workflow field updates, fires before and after triggers one more time. Custom validation rules are not run again.
9. Executes escalation rules.
10. 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.
11. 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.
12. Executes Criteria Based Sharing evaluation.
13. Commits all DML operations to the database.
14. Executes post-commit logic. Ex: Sending email.

15.What is the trigger handler?
Ans:

16.How do we avoid recursive triggers?
Ans: Use a static variable in an Apex class to avoid an infinite loop. Static variables are local to the context of a Web request.

17.How many triggers we can define on a object?
Ans: We can write more than one trigger But it is not recommended .Best practice is One trigger On One object. 

18.Can we define triggers with same event on single object?
Ans:

19.Tell me more scenarios where you have written triggers?
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20.What is the best scenario that you have developed on triggers?
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21.How many time workflow filed update will be called in triggers?
Ans: