Nishant Rana's Weblog

 // related lead records of contact
                    QueryExpression query = new QueryExpression("lead");                    
                    query.ColumnSet = new ColumnSet(true);

                    // contact and lead - 1 - n relationship
                    Relationship relationship = new Relationship("lead_parent_contact");
                    relationship.PrimaryEntityRole = EntityRole.Referenced;

                    RelationshipQueryCollection relatedEntity = new RelationshipQueryCollection();
                    relatedEntity.Add(relationship, query);

                    RetrieveRequest request = new RetrieveRequest();
                    request.RelatedEntitiesQuery = relatedEntity;
                    request.ColumnSet = new ColumnSet(true);
                    request.Target = new EntityReference("contact", new Guid("ca0aa844-57c6-ec11-a7b6-00224826af1e"));

                    RetrieveResponse response = (RetrieveResponse)svc.Execute(request);
                    var contactToBeCloned = response.Entity;                   
                    var clonedContact = contactToBeCloned.Clone(true);

                    // remove attribute that can cause error from main entity             
                    clonedContact.Id = Guid.NewGuid();
                    clonedContact.Attributes.Remove("contactid");                    
                    clonedContact.Attributes.Remove("address1_addressid");
                    clonedContact.Attributes.Remove("address2_addressid");
                    clonedContact.Attributes.Remove("address3_addressid");

                    // remove attribute that can cause error from child / related entities
                    foreach (var relatedEntities in clonedContact.RelatedEntities)
                    {
                        foreach(var leadEntity in relatedEntities.Value.Entities)
                        {
                            leadEntity.Id = Guid.NewGuid();
                            leadEntity.Attributes.Remove("leadid");
                            leadEntity.Attributes.Remove("address1_addressid");
                            leadEntity.Attributes.Remove("address2_addressid");
                        }
                    }
                    svc.Create(clonedContact);