This document discusses Apex collection design patterns in Salesforce. It defines collections as objects that can hold references to other objects or sObjects. The main types of collections are Lists, Sets, and Maps. Lists store elements in order and allow duplicates, Sets store unique elements in any order, and Maps store key-value pairs with unique keys. The document provides examples of using each collection type with sObjects and primitive data. It also presents two patterns for mapping contacts to accounts using collections, with one taking fewer script lines to execute.

1. Apex Collection Design Pattern
Sathishkumar Periyasamy
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2. Agenda
• What is Collections?
• Type of collections
• Explain List, Set, Map
• Collection Patterns
• Summary

3. What is collection?
• Collection is nothing but an array(call it other computer language).
• Collection is an object that can hold reference of other object or
sObject.
• Strongly typed as object or sObject.
• There is no limitation to store the value on the collection but think
about heap size issue.

4. Type of Collection
• There are 3 type of collection :
• List
• Set
• Map

5. List
• List is basic type of array(other computer language).
• List can hold primitive, object, sObject
• Stored in ordered received data.
• sObject List can be sort by Name and Standard Fields.
• DML operation allowed sObject List.
• List allow duplicate entries.
• Can be used used in SOQL query in the filter condition and store query result.
• 2 way you can declare list in apex code.
• List<String> lstStrting = new List<Strting>();
• String[] aryString;
• 2 way you can access list in apex code.
• lstString.get(i);
• aryString[i];

6. List Example
List of sObject:
List<Account> lstAccount = new List<Account>();
lstAccount = [Select Id, Name from Account limit 10];
List<Contact> lstContact = new List<Contact>();
lstContact = [Select Id, AccountId from Contact where AccountID IN:lstAccount ];
Another Way (Using single query to get both account and contact):
List<Account> lstAccount = new List<Account>();
lstAccount = [Select Id, Name, (Select Id, AccountId from Contacts) from Account
limit 10];

7. List Example
Primitive List:
List<String> lstString = new List<String>();
List<account> lstAccount = [Select Id, Name from Account limit 10];
for(Account iterator : lstAccount) lstString .add(iterator.Name);
Object List (Use wrapper class on the List):
List< wrapper> lstWrapper = new List< wrapper>();
List<account> lstAccount = [Select Id, Name from Account limit 10];
for(Account iterator : lstAccount) {
lstWrapper.add(new wrapper(iterator.Name, iterator.Id));
}
Wrapper Class:
Public class wrapper {
String strName;
Id accountID;
public wrapper (String strAccName, Id accountID){
this.strName = strAccName;
this. accountID = accountID
}
}

8. Set
• Set is basically a hash table.
• Set item should be unique.
• Data not stored in order receiving.
• Set can hold primitive, object, sObject - Better to stay with primitive
type.
• Can be used used in SOQL query in the filter condition.
• Set can be pass to the list constructor.

9. Set Example
Set of sObject:
Set<Account> setAccount = new set<Account>();
Account objAccount = new Account(Name = ‘Salesforce’);
setAccount.add(objAccount);
objAccount.Name = ‘Force.com’;
setAccount.add(objAccount);
Result : Set size will be “2” because Set is unique.
Note : you should be very careful while using sObject in the Set.

10. Set Example
Set of primitive data type:
Set<Id> setAccount = new set<Id>();
List<Account> lstAccount = [Selecte Id from Account];
for(Account iterator : lstAccount) {
setAccount.add(iterator.Id);
}
Set<String> setAccountFormatching = new set<String>();
List<Account> lstAccount = [Selecte Id, Name, Email from Account];
for(Account iterator : lstAccount) {
setAccount.add(iterator.Name + ’’ + iterator.Email);
}
Note : you can concatenate many fields into single string. This can be used for some kind
of matching logic.

11. Map
• Map is also hash table with Key and Value pair.
• Key is Unique.
• Value is associated values to that Key. This can hold – List, Set, Map,
Primitive data type, object and sObject.
• You can’t use map in the DML/SOQL Query directory
• Use Map.Values() method in DML – Value should be sObject.
• Use Map.keySet() method in SOQL query.

12. Map Example
Map of sObject:
Map<Id, Account> mapAccount = new Map<Id, Account>([Select Id, Name from
Account where….......]);
System.debug(‘Only Id : ’+ mapAccount.keySet()); -- use this in soql query.
System.debug(‘Only List of Account : ’+ mapAccount.values()); -- use this in DML.
Nested Map:
Map<Id, Map<Id, Map<String, …>>> mapAccount = new Map<Id, Map<Id,
Map<String, …>>>();
Note : Nested Map used for most complex business logic.

13. Collection Patterns
• When you want to pull contact my account Id. Want to store contact for particular account Id.
Pattern 1:
List<Contact> lstContact = [Select Id, accountid from contact where accountid IN:setAccountId];
Map<Id, List<Contact>> mapContactByAccount = new Map<Id, List<Contact>> ();
for(Contact iterator : lstContact) {
if(!mapContactByAccount.contacsKey(iterator.AccountID)) {
mapContactByAccount.put(iterator.AccountID, new List<Contact>());
}
mapContactByAccount.get(iterator.AccountID).add(iterator);
}
Pattern 2:
List<Account> lstAccount = [Select Id, (Select Id, Name from Contacts) from account where ID IN:setAccountId];
Map<Id, List<Contact>> mapContactByAccount = new Map<Id, List<Contact>> ();
for(Account iterator : lstAccount) {
iteratorChild.put(iterator.Id, iterator.Contacts);
}
Note : Pattern 1 will take more script line execution but Pattern 2 will take less script line execution.

14. Summary
• Talked about type of collection.
https://developer.salesforce.com/docs/atlas.en-
us.apexcode.meta/apexcode/langCon_apex_collections.htm
• Collection patters
- Go through Dan Appleman online video -
https://app.pluralsight.com/library/courses/apex-fundamentals/table-of-
contents

15. Thank You