fabric之chaincode方法GetHistoryForK

随时间返回键值的历史记录。对于每一个历史的key更新，历史的值，有关联的交易ID和时间戳会被返回，这个时间戳是客户端在提案头部提供的，GetHistoryForKey需要peer的配置参数core.ledger.history.enableHistoryDatabase为true，在验证阶段查询不会被预执行。也就是说其他已经提交的交易可能同时已经更新key，也同时影响结果集，并且在验证和提交阶段这个不会被检测到，应用程序易受此影响因此不应该使用GetHistoryForKey作为事务的一部分更新分类账，并且应该限制使用只读链代码操作。

/args:name hashvalue owner
func (sc *SimpleChaincode) queryHistoryAsset(stub shim.ChaincodeStubInterface, args []string) pb.Response {
    if len(args) < 3 {
        return shim.Error("Incorrect number of arguments. Expecting 1")
    }

    name := args[0]
    hashvalue := args[1]
    owner := args[2]
    kk, _ := stub.CreateCompositeKey(name, []string{hashvalue, owner})
    fmt.Printf("- start getHistoryForMarble: %s\n", kk)

    resultsIterator, err := stub.GetHistoryForKey(kk)
    if err != nil {
        return shim.Error(err.Error())
    }
    defer resultsIterator.Close()

    // buffer is a JSON array containing historic values for the marble
    var buffer bytes.Buffer
    buffer.WriteString("[")

    bArrayMemberAlreadyWritten := false
    for resultsIterator.HasNext() {
        response, err := resultsIterator.Next()
        if err != nil {
            return shim.Error(err.Error())
        }
        // Add a comma before array members, suppress it for the first array member
        if bArrayMemberAlreadyWritten == true {
            buffer.WriteString(",")
        }
        buffer.WriteString("{\"TxId\":")
        buffer.WriteString("\"")
        buffer.WriteString(response.TxId)
        buffer.WriteString("\"")

        buffer.WriteString(", \"Value\":")
        // if it was a delete operation on given key, then we need to set the
        //corresponding value null. Else, we will write the response.Value
        //as-is (as the Value itself a JSON marble)
        if response.IsDelete {
            buffer.WriteString("null")
        } else {
            buffer.WriteString(string(response.Value))
        }

        buffer.WriteString(", \"Timestamp\":")
        buffer.WriteString("\"")
        buffer.WriteString(time.Unix(response.Timestamp.Seconds, int64(response.Timestamp.Nanos)).String())
        buffer.WriteString("\"")

        buffer.WriteString(", \"IsDelete\":")
        buffer.WriteString("\"")
        buffer.WriteString(strconv.FormatBool(response.IsDelete))
        buffer.WriteString("\"")

        buffer.WriteString("}")
        bArrayMemberAlreadyWritten = true
    }
    buffer.WriteString("]")

    fmt.Printf("- getHistoryForMarble returning:\n%s\n", buffer.String())

    return shim.Success(buffer.Bytes())

}

运行结果：