Apex

Apex is a strongly typed, object-oriented programming language that allows developers to execute flow and transaction control statements on Salesforce servers in conjunction with calls to the API. Using syntax that looks like Java and acts like database stored procedures, Apex enables developers to add business logic to most system events, including button clicks, related record updates, and Visualforce pages. Apex code can be initiated by Web service requests and from triggers on objects.

When a developer writes and saves Apex code to the platform, the platform application server first compiles the code into an abstract set of instructions that can be understood by the Apex runtime interpreter, and then saves those instructions as metadata.

When an end user triggers the execution of Apex, the platform application server retrieves the compiled instructions from the metadata and sends them through the runtime interpreter before returning the result. The end user observes no differences in execution time from standard platform requests.

Apex can be used to:

• Create Web services.
• Create email services.
• Perform complex validation over multiple objects.
• Create complex business processes that are not supported by workflow.
• Create custom transactional logic (logic that occurs over the entire transaction, not just with a single record or object).
• Attach custom logic to another operation, such as saving a record, so that it occurs whenever the operation is executed, regardless of whether it originates in the user interface, a Visualforce page, or from SOAP API.

Apex cannot be used to:

• Render elements in the user interface other than error messages
• Change standard functionality
  • Apex will prevent this functionality from happening, or add additional functionality
• Create temporary files
• Spawn threads

Writing tests

Testing is the key to successful long-term development and is a critical component of the development process. We strongly recommend that you use a test-driven development process, that is, test development that occurs at the same time as code development.

Apex supports the creation and execution of unit tests.

• Unit tests are class methods that verify whether a particular piece of code is working properly.
• Unit test methods take no arguments, commit no data to the database, and send no emails.
  • Such methods are flagged with the @IsTest annotation in the method definition.
  • Unit test methods must be defined in test classes, that is, classes annotated with @IsTest.
• Unit tests must cover at least 75% of your Apex code, and all of those tests must complete successfully.

• Example

 public static void updateOlderAccounts() {
        // Get the 2 oldest accounts and change their description to 'Old Account'
        Account[] oldAccounts = [SELECT Id, Description FROM Account ORDER BY CreatedDate ASC LIMIT 2];
        // loop through them and update the Description field
        for (Account acct : oldAccounts) {
            acct.Description = 'Old Account';
        }
        // save the change you made
        update oldAccounts;
  }
  // run it 
  updateOlderAccounts();
      

Demo

• Run the query to find the old accounts

cat oldAccounts.soql 

SELECT Id, Description FROM Account ORDER BY CreatedDate ASC LIMIT 2

sfdx mohanc:data:query  -u mohan.chinnappan.n.sel2@gmail.com -q oldAccounts.soql -f json      

[
    {
        "attributes": {
            "type": "Account",
            "url": "/services/data/v57.0/sobjects/Account/0018W000024fLocQAE"
        },
        "Id": "0018W000024fLocQAE",
        "Description": "Genomics company engaged in mapping and sequencing of the human genome and developing gene-based drugs"
    },
    {
        "attributes": {
            "type": "Account",
            "url": "/services/data/v57.0/sobjects/Account/0018W000024fLoaQAE"
        },
        "Id": "0018W000024fLoaQAE",
        "Description": "TODO"
    }
]

cat UpdateOlderAccounts.cls 

    public static void updateOlderAccounts() {
        // Get the 2 oldest accounts and change their description to 'Old Account'
        Account[] oldAccounts = [SELECT Id, Description FROM Account ORDER BY CreatedDate ASC LIMIT 2];
        // loop through them and update the Description field
        for (Account acct : oldAccounts) {
            acct.Description = 'Old Account';
        }
        // save the change you made
        update oldAccounts;
    }

    // run it
    updateOlderAccounts();

• Execute

sfdx mohanc:tooling:execute -u mohan.chinnappan.n.sel2@gmail.com  -a UpdateOlderAccounts.cls    

apexCode:     public static void updateOlderAccounts() {
        // Get the 2 oldest accounts and change their description to 'Old Account'
        Account[] oldAccounts = [SELECT Id, Description FROM Account ORDER BY CreatedDate ASC LIMIT 2];
        // loop through them and update the Description field
        for (Account acct : oldAccounts) {
            acct.Description = 'Old Account';
        }
        // save the change you made
        update oldAccounts;
    }
    // run it
    updateOlderAccounts();

compiled?: true
executed?: true
{
  line: -1,
  column: -1,
  compiled: true,
  success: true,
  compileProblem: null,
  exceptionStackTrace: null,
  exceptionMessage: null
}

• Check the results after execution

sfdx mohanc:data:query  -u mohan.chinnappan.n.sel2@gmail.com -q oldAccounts.soql -f json    

[
    {
        "attributes": {
            "type": "Account",
            "url": "/services/data/v57.0/sobjects/Account/0018W000024fLocQAE"
        },
        "Id": "0018W000024fLocQAE",
        "Description": "Old Account"
    },
    {
        "attributes": {
            "type": "Account",
            "url": "/services/data/v57.0/sobjects/Account/0018W000024fLoaQAE"
        },
        "Id": "0018W000024fLoaQAE",
        "Description": "Old Account"
    }
]

• Apex Developer Guide
• Apex Quick Start