The very core of Hyperledger Fabric is Chaincode, you need a Chaincode to read and write data to the World State. There is a syntax for writing your Chaincode. The Chaincode has two methods Init and Invoke, Init is called when the chaincode is instantiated and Invoke when the chaincode is invoked or queried. Both these method has the same return type pb.Response.
shim.putState(Key, Byte Stream) – Will store the data
shim.GetState(Key) – Retrieves the data based on the key
shim.DelState(Key) – Will delete the data based on the key
Below is a simple Chaincode to store, query and delete data in World store.
package main
import (
"github.com/hyperledger/fabric/core/chaincode/shim"
pb "github.com/hyperledger/fabric/protos/peer"
)
var logger = shim.NewLogger("example_chaincode")
type SimpleChaincode struct {
}
/**
* Init is called when the Chaincode is Instantiated
*
**/
func (t *SimpleChaincode) Init(stub shim.ChaincodeStubInterface) pb.Response {
logger.Info("########### example_chaincode Init ###########")
_, args := stub.GetFunctionAndParameters()
var A, B string
A = args[0]
B = args[1]
err := stub.PutState(A, []byte(B))
if err != nil {
return shim.Error(err.Error())
}
return shim.Success(nil)
}
/**
* Invoke is called whenever the Chaincode is called.
*
**/
func (t *SimpleChaincode) Invoke(stub shim.ChaincodeStubInterface) pb.Response {
logger.Info("########### example_chaincode Init ###########")
function, args := stub.GetFunctionAndParameters()
var A, B string
A = args[0]
if function == "delete" {
//The Stored data is deleted
err := stub.DelState(A)
if err != nil {
return shim.Error("Failed to delete state")
}
return shim.Success(nil)
}
if function == "query" {
//Retrieving the data from the World State, of the data is not present error is thrown
Avalbytes, err := stub.GetState(A)
if err != nil {
jsonResp := "{\"Error\":\"Failed to get state for " + A + "\"}"
return shim.Error(jsonResp)
}
return shim.Success(Avalbytes)
}
if function == "setdata" {
//Storing the data to the World State
B = args[1]
err := stub.PutState(A, []byte(B))
if err != nil {
return shim.Error(err.Error())
}
return shim.Success(nil)
}
logger.Errorf("Unknown action, check the first argument, must be one of 'delete', 'query', or 'setdata'. But got: %v", args[0])
return shim.Error("Unknown action, check the first argument, must be one of 'delete', 'query', or 'setdata'. But got: %v"+ args[0])
}
func main() {
err := shim.Start(new(SimpleChaincode))
if err != nil {
logger.Errorf("Error starting Simple chaincode: %s", err)
}
}
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