linq subquery for in

for example following sql

select * from AccountTransactions  a
where
a.TransactionId =19687 OR
a.TransactionId  in (select ChildId from AccountTransactionRelations where InvoiceId=19687)

will have this equivalent in linq:

var records = from t in odc.AccountTransactions
	join r in odc.AccountTransactionRelations on t.TransactionId equals  r.InvoiceId into rel
	where t.TransactionId == transactionId || rel.Select(o => o.ChildId).Contains(transactionId)
	select t;