Run Salesforce Case Assignment Rule from Apex Trigger

From a standard UI, a user can trigger assignment rules by simply checking the "Assign using active assignment rules" checkbox under the Optional section. The problem arises when your app needs to insert the Case from Apex and wants to trigger assignment rules. Using this script, a Case will be inserted but assignment rules will not be triggered as there is no such field "Assign using active assignment rules" on Case.

//Instance of case
Case newCase = new Case(Status = 'New') ;
//Inserting a Case
insert newCase ;

Running Case Assignment Rules from Apex

A solution is using Database.DMLOptions. The Database.DMLOptions class can provide extra information during a transaction, like specifying the truncation behavior of fields or assignment rule information. For example, the script below is fetching the assignment rules from Case and then creating the DMLOptions for the "Assign using active assignment rules" checkbox.

//Fetching the assignment rules on case
AssignmentRule AR = new AssignmentRule();
AR = [select id from AssignmentRule where SobjectType = 'Case' and Active = true limit 1];

//Creating the DMLOptions for "Assign using active assignment rules" checkbox
Database.DMLOptions dmlOpts = new Database.DMLOptions();
dmlOpts.assignmentRuleHeader.assignmentRuleId= AR.id;

Case newCase = new Case(Status = 'New') ;
//Setting the DMLOption on Case instance
newCase.setOptions(dmlOpts);
insert newCase ;

Now when the Case is inserted using this script, the assignment rules get triggered.