March 2019
Intermediate to advanced
636 pages
27h 50m
English
book
Blockchain Development with Hyperledger
by Salman A. Baset, Luc Desrosiers, Nitin Gaur, Petr Novotny
Content preview from Blockchain Development with Hyperledger
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Composite keys
We often need to store multiple instances of one type on the ledger, such as multiple trade agreements, letters of credit, and so on. In this case, the keys of those instances will be typically constructed from a combination of attributes—for example, "Trade" + ID, yielding ["Trade1","Trade2", ...]. The key of an instance can be customized in the code, or API functions can be provided in SHIM to construct a composite key (in other words, a unique key) of an instance based on a combination of several attributes. These functions simplify composite key construction. Composite keys can then be used just as a normal string key is used to record and retrieve values using the PutState() and GetState() functions.
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