Advanced contract design topics

In the following sections, we will explore topics that allow us to develop fully functional contracts including cross-contract and cross-ledger invocations, composite keys, querying techniques, indexing of data, and explain the key transaction mechanisms.

Cross-contract and cross-ledger invocation

In complex business process workflows spanning multiple contracts and channels, a contract may need to invoke other contracts as parts of its logic. In our solution, this happens when transactions of LetterOfCreditContract and ExportLicenseContract require information from TradeContract about TradeAgreements.

Both Contract APIs provide function invokeChaincode, which calls the contract within the same or a different channel. The Java Contract API has the additional invokeChaincodeWithStringArgs, which simplifies the handling of string arguments.

The functions use the transaction context of the calling function to invoke the contract and thus...