Introduction to Apex

Each year we are having struggle training fresh graduate from the University into learning the basic of Salesforce Apex programming language. They mixed up the syntax with what Java would look like.
So we came up with a list of things that would speed up the process of training.

Here's a list of the commonly used syntax in Apex and restrictions:

Hope this tutorial is useful to you.

Cheers!

# Intro to apex

## Basic operation
``` java
//variable declaration
Integer val = 0;
string str = 'Super test'; // apex allow only single quote for string variable
boolean isDeleted = true;

/*Concatenate string*/
string firstname = 'John';
string lastname = 'Doe';
string name = firstname + ' ' +  lastname;
```

## Debug Apex code
``` java
string name = 'Super test';
system.debug('### '+name); // ### Super test

```

## Collection
A collection in apex is either a "List", "Set" or a "Map"

``` java
/**
* List
*/
//Populating method 1
list<string> carList = new list<string>();  //initializing an empty list
/*Populating the list*/
carList.add('Honda');
carList.add('Toyota');
carList.add('Mazda');

//Populating method 2
list<string> carList = new list<string>{'BMW', 'Mercedes', 'Audi'};

/**
* Set
*/
set<string> referenceSet = new set<string>();
referenceSet.add('test');
//or
set<string> referenceSet = new set<string>{'test'};

/**
* Map
* A map consists of a key and value. The key should always be a primitive type (string, integer, id, ...).
*/
map<string, string> countryCodeMap = new map<string, string>(); //initiliazing an empty map
//Populating a map
countryCodeMap.put('Mauritius', 'MU');
countryCodeMap.put('France', 'FR');
//or
map<string, string> countryCodeMap = new map<string, string>{'Mauritius'=>'MU', 'France'=>'FR'};

//accessing a value for a specific key in the map
string franceCode = countryCodeMap.get('France'); //returns FR
```

## sObject
Any standard and custom object in Salesforce is represented as an sObject in Apex.

Example

| Object type | Name     | Api name (as represented in apex) |
| ----------- | ---------- | ----------------------------------- |
| Standard | Account  | Account |
| Standard | Contact | Contact |
| Custom | Car | Car__c |
| Custom | Job | Job__c |

``` java
//Create a new instance of an sObject
Contact con1 = new Contact(); //initializing an instance of a contact
con1.Firstname = 'Jane';
con1.Lastname = 'Doe';

// or
Contact con1 = new Contact(Firstname='Jane', Lastname='Doe');

/*custom object*/
Job__c job = new Job__c();

//creating an instance of an existing record
Account salesFr = new Account(Id='0012400000YwpHM'); //you just need to instantiate with the field "Id"

```

### Note
A lookup or master-detail relationship fields in apex is represented by an Id.

## DML
DML operations consists of:
- insert
- update
- upsert
- delete
- undelete
- merge

### Insert
```java
Account telecom = new Account(Name='Telecom');
insert telecom;
```
### Update
```java
telecom.Name = 'Telecom - Head office';
update telecom;
```
### Upsert
It does an insert if record not found else update if found.
Generally use with an ExternalId (a flag on a field to make it an index)
```java
//account does not exist
Account sbm = new Account(Name='SBM');
upsert sbm; // will create an account with Name = SBM
//account exist
Account sbm = new Account(Id='0012400000YwpHM', Name='SBM - Closed');
upsert sbm; // will update with Name = 'SBM - Closed'

//update a contact based on its external id (here Email is defined as external id)
Contact con1 = new Contact(Email='plop@test.com', Lastname='Plop');
upsert con1 Contact.Email;
```
### Delete and Undelete
Can only delete instance which contains an Id.
```java
Account sbm = new Account(Id='0012400000YwpHM');
delete sbm;

undelete sbm;
```

## SOQL queries
SOQL query will always return the following:
- an sobject
- a list of sobjects
- a list of objects

### Basic query
```java
//Returning only one record
Contact jane = [SELECT Id, Firstname, Lastname FROM Contact WHERE Id = '0032400000GRVvY'];

//returning a list of record
list<Account> accountList = [SELECT Id, Name FROM Account];
```
### Advanced query
```java
// returning a list of contact with their account name
list<Contact> contactList = [SELECT Id,
                                    Firstname,
                                    Lastname,
                                    Account.Name
                            FROM Contact
                            WHERE AccountId != null];

// returning list of account with their children(contacts)
list<Account> accountList = [SELECT Id, Name,
                                (SELECT Id, Firstname, Lastname from Contacts)
                            FROM Account];
```
Notice that the child relationship is in plural.
If a custom object was used here
- parent relationship: objectName**__r**
- child relationship: objectName**s__r**


## Loops
``` java
for(integer i = 0; i < size; i++){
  // code here
}

/*Example*/
list<string> firstnames = new list<string>{'John', 'Jane'};
list<string> lastnames = new list<string>{'Smith', 'Doe'};
list<string> names= new list<string>();
for(integer i = 0; i < firstnames.size(); i++){
  string name = firstnames[i] + ' ' + lastnames[i];
  names.add(name);
}

//or
for(type variable: list<type>){
  //do any operation with variable
}

/*Examples*/
integer total = 0;
list<Account> accountList = [SELECT id, NumberOfEmployees FROM Account];
for(Account acc: accountList){
  if (acc.NumberOfEmployees != null){
    total = total + acc.NumberOfEmployees;
  }
}

```

## Classes and Methods
``` java
public class Employee {
  public string name;
  public integer age;
  public datetime arrivedAt;
  public Employee(){
  }
  public void checkIn(){
    //void just do the action
    arrivedAt = System.now();
  }
  public boolean shouldRetire(){
    integer diff = 65 - age;
    if (diff <= 0){
      return true;
    }
    return false;
  }
  public static integer numEmployees(){
    list<Employee__c> employees = [select id from Employee__c];
    return employees.size();
  }
}

//Creating an instance of employee
Employee emp = new Employee();
emp.name = 'john';
emp.age = 30;
//call checkIn method for the employee
emp.checkIn(); // void method do the action only
retired = emp.shouldRetire(); // non void method should return a value

//Calling static methods
Employee.numEmployees();
```