How Parent and Child record can be inserted in Single Statement : Use of External id field

Date dt = Date.today().addDays(7);

2	Opportunity newOpportunity = new Opportunity(Name = 'shivasoft', StageName ='Prospecting', CloseDate = dt);

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/*

5	Create the parent reference. Used only for foreign key reference  and doesn't contain any other fields. If we provide any other value it will give following error

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7	System.DmlException: Insert failed. First exception on row 1; first error: INVALID_FIELD, More than 1 field provided in an external foreign key reference in entity: Account: []

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*/

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10	Account accountReference = new Account(MyExtID__c = 'SHIVA1234567');

11	newOpportunity.Account = accountReference;

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13	//  Create the Account object to insert.  Same as above but has Name field.  Used for the insert.

14	Account parentAccount = new Account(Name = 'Shiva', MyExtID__c = 'SHIVA1234567');

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16	Database.SaveResult[]

17	results = Database.insert(new SObject[] {  parentAccount, newOpportunity });

Note : parent object should be included before the child object in list otherwise you will get following error : 

 INVALID_FIELD, Foreign key external ID: SHIVA1234567 not found for field  MyExtID__c  in entity Account: []