Basics of Apex Trigger for beginners

The basic logic of trigger is too huge to cover, I have tried a bit to make everyone understand that how this Apex trigger, a "pain in ass" works, I'll go step by step process of writing apex triggers.

What is Apex Triggers ?

A Trigger is Apex code that executes before or after the following types of operations:

• insert
• update
• delete
• merge
• upsert
• undelete

Types of Apex Triggers

• Before Triggers: Before triggers can be used to update or validate record values before they are saved to the database.
• After Triggers: After triggers can be used to access field values that are set by the database (such as a record's Id or last Updated field), and to affect changes in other records, such as logging into an audit table or firing asynchronous events with a queue.

Example : before insert, after insert, before update, after update, before delete, after delete

Syntax of Trigger

Things to keep in mind while writing apex trigger

• Bulkify your Code : Use Looping through Trigger’s collections variables instead of process through particular indexing.
• All triggers are bulk triggers by default, and can process multiple records at a time.
• Bulk triggers can handle both single record updates and bulk operations like: Data import, Force.com Bulk API calls.
• Bulkify your Code : Use Looping through Trigger’s collections variables instead of process through particular indexing.
• Avoid SOQL Queries or DML statements inside FOR Loops: An individual Apex request gets a maximum of 100 SOQL queries before exceeding that governor limit. 
• Bulkify your Helper Methods: if a trigger uses some Apex methods written in a helper class, it's important that those shared Apex methods are properly designed to handle bulk records. These methods should be written to be invoked with a set of records, especially if the method has a SOQL query or DML operation.

Use @future appropriately:

Here is a list of governor limits specific to the @future annotation:

• No more than 10 method calls per Apex invocation.
• No more than 200 method calls per Salesforce license per 24 hours.
• The parameters specified must be primitive datatypes, arrays of primitive datatypes, or collections of primitive datatypes.
• Methods with the future annotation cannot take sObjects or objects as arguments.
• Methods with the future annotation cannot be used in Visualforce.

Use efficient collection variable of apex triggers

Try using sets and maps to handle bulk record processing.

TRIGGER BEST PRACTICE

• Always use helper class in your trigger, and in helper class perform all your logic. like below

• Don't write more then one trigger on an object, try to add up all your new trigger in a single trigger using different-different helper classes to read more click Order of Execution

There is allot to take care of when writing apex triggers, but I found these to helpful.

Hope this helps 

Happy coding.!!!