Apex collection patterns

Apex Collection Design Pattern
Sathishkumar Periyasamy
Twitter : @ppksathish1
Facebook : https://www.facebook.com/periyasamy.sathish
LinkedIn : www.linkedin.com/in/sathishkumar-periyasamy-00039117

Agenda
• What is Collections?
• Type of collections
• Explain List, Set, Map
• Collection Patterns
• Summary

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.

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

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];

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];

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
}
}

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.

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.

Set Example
Set of primitive data type:
Set<Id> setAccount = new set<Id>();
List<Account> lstAccount = [Selecte Id from Account];
setAccount.add(iterator.Id);
}
Set<String> setAccountFormatching = new set<String>();
List<Account> lstAccount = [Selecte Id, Name, Email from Account];
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.

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.

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.

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>> ();
iteratorChild.put(iterator.Id, iterator.Contacts);
}
Note : Pattern 1 will take more script line execution but Pattern 2 will take less script line execution.

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

Apex collection patterns

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