Composite key vs Single key append strings

Question

Watching many examples in Hyperledger Fabric, I found two ways to achieve a key:

Let's say we have two fields visa and type of visa.

Visa: "1212323"

Type of Visa: "Student Visa"

We can create a key either:

1. Using CompositeKey function provide by stub

key, err := stub.CreateCompositeKey(indexName,[]string{visa, typeVisa}) stub.PutState(key, value)

2. Concatenating the two fields

stub.PutState(visa+typeVisa, value)

What is the difference between these two approaches? Which of these is best in terms of performance?

Answer 1

By using Composite Keys you will have access to extra methods in your chaincode e.g. getStateByPartialCompositeKey so you could potentially retrieve all "Student Visa". If you make your own keys you would have to retrieve all the Visas then filter the set youself, or write queries to retrieve the data by attributes (assuming you are using JSON data in a CouchDB state database.) . So I would think the performance differential is in efficient retrieval rather than the original writing of the keys.

There is a good doc in the Fabric docs on CouchDB as the State Database which covers this information.