querying data from particular node's database - corda

Question

I am doing some reporting kind of things using customer query. for that, i have to fetch the data from respective node's database.but,no clue how to do that.its normally fetching all data irrespective of node.

Answer 1

Let's do an example based on the IOU CorDapp (https://github.com/corda/cordapp-example/). There are several ways you can do this:
1. Via an API endpoint
This endpoint will return any IOUs stored on the node with a value above minValue:
#GET
#Path("ious-above-value")
#Produces(MediaType.APPLICATION_JSON)
fun getIOUsAboveValue(#QueryParam("minValue") minValue: Int): List<IOUState> {
val results = builder {
val currencyIndex = IOUSchemaV1.PersistentIOU::value.greaterThan(minValue)
val customCriteria = QueryCriteria.VaultCustomQueryCriteria(currencyIndex)
rpcOps.vaultQueryBy<IOUState>(customCriteria)
}
val stateAndRefs = results.states
return stateAndRefs.map { stateAndRef -> stateAndRef.state.data }
}
2. Via a client
This client will return any IOUs stored on the node with a value above minValue:
fun main(args: Array<String>) {
require(args.size == 1) { "Usage: ExampleClientRPC <node address>" }
val nodeAddress = NetworkHostAndPort.parse(args[0])
val client = CordaRPCClient(nodeAddress)
// Can be amended in the com.example.MainKt file.
val proxy = client.start("user1", "test").proxy
val results = builder {
val currencyIndex = IOUSchemaV1.PersistentIOU::value.greaterThan(3)
val customCriteria = QueryCriteria.VaultCustomQueryCriteria(currencyIndex)
proxy.vaultQueryBy<IOUState>(customCriteria)
}
val stateAndRefs = results.states
val states = stateAndRefs.map { stateAndRef -> stateAndRef.state.data }
}
3. Via the node's database directly
You can log into the node's database by following the instructions here: https://docs.corda.net/node-database.html. You will then be able to execute SQL queries against the node's database directly.