sfdc-learn #5 : How to insert a Parent with multiple child's in one single DML in apex.

    // First create a ExterNalId__c as a custom field with External Id Options on Parent object.

    List<SObject> sObjectLst =  new List<SObject>();

    // Create the parent reference. Used only for foreign key reference and doesn't contain any other  fields.

    Account accRef = new Account(ExterNalId__c = 'externalIdValue'); 

    // Create a child record or many records

    For(Integer i = 0 ; i<3;i++){

        Contact con = new Contact();

        con.Firstname = 'ConFirst'+i;

        con.Lastname = 'ConLast'+i;

        con.Account = accRef;  // Assign this created parent reference to that parent relation field. 

        sObjectLst.add(con);  // Add these child records in list.

    }

    // Create parent record with initializing required fields and  externalId field.

    Account acc = new Account(Name='Acc Name',ExterNalId__c = 'externalIdValue');

    sObjectLst.add(acc); // Add parnet record in list.

    // Insert list

    Database.SaveResult[] results = Database.insert(sObjectLst);  // Check results. 

    for (Integer i = 0; i < results.size(); i++) { 

            if (results[i].isSuccess()) {

                System.debug('Successfully created ID: '+ results[i].getId());

            } else {

                   System.debug('Error: could not create sobject '+ 'for array element ' + i + '.');

                   System.debug('   The error reported was: '+ results[i].getErrors()[0].getMessage() + '\n');

            }

    }