Collections in Salesforce
Collections:- Collections are the group of similar types Apex has the following types of Collections
- Lists
- Maps
- Sets
There is no limit on the number of items a collection can hold However there is a general limit on heap size.
Lists
A list is an ordered collection of typed primitives SObjects, user-defined objects, Apex objects or collections that are distinguished by their includes.
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- The index position of the first element in a list is always ‘0’
- To declare a list, use the list keyword followed by the primitive data, SObject, nested list, map, or set type within < > characters
List< String > Mylist= new list<string>();
This will store the block of memory at the database
List <List<set<Integer>>>mylist2= new list <list<set<Integer>>>(); Nested List
Note:- A list can only contain up to five levels of nested collections inside it.
*The following example describes us about the retrieving 100 accounts stored in variable.
List<Account> accs= select Id,Name FROM Account limit 100 ;
*To access elements in a list, use the system methods provided by Apex.
Ex:- List<Integer> Li=new list<Integer>(); Define a new List
Li.add(47); adds a second element of value 47 to the end of the list
Integer x= Li.get(1);Retrieves the element at index 1.
Li.Set(0,73); adds the integer 73 to the list at index o
Li.clear(); ---> removes all elements from the list
*Go to the Developer console and execute the following code and check the result by going through USER-DEBUG
List<String> Li=new List<string>();
Li.add('Anil');
Li.add('sateesh');
Li.add('nagaraju');
System.debug(Li); à the o/p from this line is
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String name = Li.get (0);System.debug (name); ---> the o/p from this line is ANIL
Li.set(2, ‘sanjeev’);
System debug (Li); ---> the o/p from this line is
Li.clear (); ---> clear all elements in a list
System.debug (li); ---> the o/p from this line is null.
Note:- In a list, we can add Duplicate values that is duplicate values will be allowed inside a list.
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Sets
A set is an unordered collection of primitives or SObjects that do not contain any duplicate elements.To declare a set, use the set keyword followed by the primitive data type name within < > characters
Ex:-
set <string> s= new set < string > ();To access elements in a set use the system methods provided by Apex.
<Integer> s=new set <Integer>(); ---> Define a new set
S.add (1); ---> Adding an element to the set
Boolean b= s.contains(1); ---> It will returns true when the element ‘1’ contains within the set.
s.remove (1); ---> Remove the element from the set
*Go to the Developer console and execute the following code and check the result by going through USER-DEBUG();
Set <string> s=new set <string>(); s.add(‘red’);
s.add(‘bule’);
s.add(‘Black’);
s.add('green');
system.debug (s);
This statement gives the o/p below
{Black, blue ,green ,red ]
s.remove ('green'); system.debug (s);
This statement gives the Output as below {Black, blue, red}
s.add ('red'); system.debug(s)
#### This statement gives the o/p as below
{black, blue, red} because the set will not allow duplicate values inside it Boolean b= s.contains ('black')
###Returns true when the value 'black' is within set and it returns "False" when the value 'black' is not there within set.
*Uniqueness of sobjects is determined by comparing fields
EX:-If we try to add two accounts with the same name to a set,only one is added.
//Create two accounts a1 and a2Account a1=new account (Name='Test Account');
Account a2=new account (Name='Test Account');
//Add both accounts to the new set
set<Account> acc set = new set <Account > {a1,a2};
system.assertEquals (accset.size(),1);
This statement is used to verify the set only contains one item.
Maps:-
A map is a collection of key-value pairs where each unique key maps to a single value
*Keys can be any primitive datatype while values can be primitive, sobject, collection type or Apex object.
*To declare a map, use the Map keyword followed by the data types of the value within < > characters
EX:-
Map < string, string> m=new map <string, string> ();Map<ID, set<string>> m1=new Map<ID, set <string>>();
Map<ID, Map <ID,Account []>> m2=new map<ID,Map<ID,Account[]>>m2;
Similar to lists, map values can contain any collection and can be nested within one another. A map can only contain up to five levels of nested collections inside it.
The following example gives the information about how a map of contain and currencies
Country ----> Key
currency---> Value
Map<string, string> m= new Map<string> ();
m.put (‘India’, 'Rupee’);
m.put (‘us’, 'Dollar'); Insert a new key value pair in the map
m.put (‘uk’, 'Pounds');
system.debug (m); the o/p of this line will be
{India= Rupee, us=Dolar, uk= pounds}
string currency = m.get('uk'); àRetrieve a value given a particular key system.debug (currency), à the o/p of this will be pounds
system.debug (m.keyset ()); à Return a set that contains all of the keys in the map.
system.debug (m.containkey ('uk'));
This statement gives the true or false whether for particular key have a value or not.
* EX:- Account a= new Account (Name='capital',Bullingcity='Hyd'); Map<Integer, Account> map1=new map<integer, Account> (); map1.put (1, a); àInsert a new key value pair in the map Map<Integer, Account >map2=map1.clone ();
###Makes a duplicate copy of the map system.debug ((map1.get (1) Billingcity));
###This statement gives the Billingcity filed value of the value pair that is assigned to the key 1.
Hyd