Corda 中的离账数据存储

Question

我想存储账本数据并仅从一个节点查询 我已经检查了this。为了将数据存储在表中，我遵循了flow cookbook of Corda 中给出的创建事务构建器的常规协议，但在记录事务时很受打击。

是否可以使用 FinalityFlow 来记录交易或必须使用 Service Hub 中的 recordTransactions 功能记录交易？

记录账外数据的首选方式是什么？

提前致谢

Answer 1

您应该通过直接在流中写入节点数据库来记录账外数据。

Flow DB 示例here 是执行此操作的 CorDapp 示例。它创建了一个DatabaseService，它存在于节点上并读写节点的数据库：

@CordaService
open class DatabaseService(private val services: ServiceHub) : SingletonSerializeAsToken() {

    companion object {
        val log = loggerFor<DatabaseService>()
    }

    /**
     * Executes a database update.
     *
     * @param query The query string with blanks for the parameters.
     * @param params The parameters to fill the blanks in the query string.
     */
    protected fun executeUpdate(query: String, params: Map<Int, Any>) {
        val preparedStatement = prepareStatement(query, params)

        try {
            preparedStatement.executeUpdate()
        } catch (e: SQLException) {
            log.error(e.message)
            throw e
        } finally {
            preparedStatement.close()
        }
    }

    /**
     * Executes a database query.
     *
     * @param query The query string with blanks for the parameters.
     * @param params The parameters to fill the blanks in the query string.
     * @param transformer A function for processing the query's ResultSet.
     *
     * @return The list of transformed query results.
     */
    protected fun <T : Any> executeQuery(
            query: String,
            params: Map<Int, Any>,
            transformer: (ResultSet) -> T
    ): List<T> {
        val preparedStatement = prepareStatement(query, params)
        val results = mutableListOf<T>()

        return try {
            val resultSet = preparedStatement.executeQuery()
            while (resultSet.next()) {
                results.add(transformer(resultSet))
            }
            results
        } catch (e: SQLException) {
            log.error(e.message)
            throw e
        } finally {
            preparedStatement.close()
        }
    }

    /**
     * Creates a PreparedStatement - a precompiled SQL statement to be
     * executed against the database.
     *
     * @param query The query string with blanks for the parameters.
     * @param params The parameters to fill the blanks in the query string.
     *
     * @return The query string and params compiled into a PreparedStatement
     */
    private fun prepareStatement(query: String, params: Map<Int, Any>): PreparedStatement {
        val session = services.jdbcSession()
        val preparedStatement = session.prepareStatement(query)

        params.forEach { (key, value) ->
            when (value) {
                is String -> preparedStatement.setString(key, value)
                is Int -> preparedStatement.setInt(key, value)
                is Long -> preparedStatement.setLong(key, value)
                else -> throw IllegalArgumentException("Unsupported type.")
            }
        }

        return preparedStatement
    }
}

Answer 2

查看以下示例，

https://github.com/corda/flow-db

在这里，您可以通过向以下位置发出 PUT 请求将令牌添加到节点的数据库表中：