Query latest world state using Hyperledger 1.0 Nodejs SDK - hyperledger-fabric

Question

Based on hyperledger SDK doc, we can use nodeJS SDK to query for the block and the transaction info. Is it possible to use this SDK to query the latest world state, e.g, query the value for a given key?

Answer 1

To being able to query for latest world state your chaincode has to provide this capability, namely you have to implement this logic and incorporate it into your chaincode. Then it will simply require to execute the chaincode to get the value for the key you are interested it.
For example you can do something similar to this:
package main
import (
"fmt"
"github.com/hyperledger/fabric/core/chaincode/shim"
"github.com/hyperledger/fabric/protos/peer"
)
// Person
type Asset struct {
ID string `json:"id"`
Name string `json:"name"`
Price string `json:"price"`
}
// assetManagement the chaincode interface implementation to manage
// the ledger of person records
type assetManagement struct {
}
func (p *assetManagement) Init(stub shim.ChaincodeStubInterface) peer.Response {
return shim.Success(nil)
}
func (p *assetManagement) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
actionName, params := stub.GetFunctionAndParameters()
if actionName == "addAsset" {
return p.addAsset(stub)
} else if actionName == "getAsset" {
return p.getAsset(stub)
}
return shim.Error("Unknown function name")
}
func (p *assetManagement) getAsset(stub shim.ChaincodeStubInterface) peer.Response {
_, params := stub.GetFunctionAndParameters()
assetID := params[0]
state, err := stub.GetState(assetID)
if err != nil {
return shim.Error(fmt.Sprintf("%s", err))
}
return shim.Success(state)
}
func (p *assetManagement) addAsset(stub shim.ChaincodeStubInterface) peer.Response {
// TODO add loggic adding new asset
}
func main() {
err := shim.Start(new(assetManagement))
if err != nil {
fmt.Printf("Error starting Simple chaincode: %s", err)
}
}
Next all you need is to invoke chaincode passing function name getAsset with asset ID and will get latest state for that asset. Here is the code based on Go SDK:
// Skipped initialization.
txRequest := apitxn.ChaincodeInvokeRequest{
Targets: []apitxn.ProposalProcessor{p},
Fcn: "getAsset",
Args: []string{"42"},
TransientMap: map[string][]byte{},
ChaincodeID: "assetChaincode",
}
proposalResponse, _, err := ch.SendTransactionProposal(txRequest)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("%v\n", proposalResponse[0].ProposalResponse)
tx, err := ch.CreateTransaction(proposalResponse)
if err != nil {
fmt.Println(err)
return
}
txResponse, err := ch.SendTransaction(tx)
if err != nil {
fmt.Println(err)
return
}
fmt.Println(txResponse[0])