var result =
    from order in dtx.Orders
    join confirmation in dtx.Confirmations
        on order.acctPoNumId equals confirmation.acctPoNumId into transactions
        from transaction in transactions.DefaultIfEmpty()
        join store in dtx.Stores
            on transaction.indexOfStore equals store.storeIndex into xStores
            from xstore in xStores
            join chain in dtx.Chains
                on xstore.indexOfChain equals chain.chainIndex into xChains