如何在Hyper-ledger Fabric中查询台账和历史数据

Question

由于账本包含一系列的业务，如何从账本中查询账本的当前状态和历史数据。

Answer 1

如果你对链码上下文中的历史数据感兴趣，你可以使用ChaincodeStubInterface应用编程接口，例如

// GetHistoryForKey returns a history of key values across time.
// For each historic key update, the historic value and associated
// transaction id and timestamp are returned. The timestamp is the
// timestamp provided by the client in the proposal header.
// GetHistoryForKey requires peer configuration
// core.ledger.history.enableHistoryDatabase to be true.
// The query is NOT re-executed during validation phase, phantom reads are
// not detected. That is, other committed transactions may have updated
// the key concurrently, impacting the result set, and this would not be
// detected at validation/commit time. Applications susceptible to this
// should therefore not use GetHistoryForKey as part of transactions that
// update ledger, and should limit use to read-only chaincode operations.
GetHistoryForKey(key string) (HistoryQueryIteratorInterface, error)

它能够检索给定键的整个历史记录，您将收到返回迭代器，它将为您提供对给定键的历史更改的洞察，例如：

historyIer, err := stub.GetHistoryForKey(yourKeyIsHere)

if err != nil {
    fmt.Println(errMsg)
    return shim.Error(errMsg)
}

if historyIer.HasNext() {
    modification, err := historyIer.Next()
    if err != nil {
        fmt.Println(errMsg)
        return shim.Error(errMsg)
    }
    fmt.Println("Returning information about", string(modification.Value))
}

另请注意，您需要确保在分类帐部分的core.yaml文件部分中启用了历史数据库：

ledger:

  history:
    # enableHistoryDatabase - options are true or false
    # Indicates if the history of key updates should be stored.
    # All history 'index' will be stored in goleveldb, regardless if using
    # CouchDB or alternate database for the state.
    enableHistoryDatabase: true

Answer 2

您可以使用QSCC查询分类账。它是用来查询对等体的系统链码。它有各种各样的查询，比如get block by number等。