步驟 4：查詢分類帳中的資料表

焦點模式

步驟 4：查詢分類帳中的資料表 - Amazon Quantum Ledger Database (Amazon QLDB)

重要

支援終止通知：現有客戶將可以使用 Amazon QLDB，直到 07/31/2025 的支援結束為止。如需詳細資訊，請參閱將 Amazon QLDB Ledger 遷移至 Amazon Aurora PostgreSQL。

在 Amazon QLDB 分類帳中建立資料表並使用資料載入資料表後，您可以執行查詢來檢閱您剛插入的車輛註冊資料。QLDB 使用 PartiQL 作為其查詢語言，而 Amazon Ion 作為其文件導向資料模型。

PartiQL 是一種開放原始碼、與 SQL 相容的查詢語言，已擴充以使用 Ion。使用 PartiQL，您可以使用熟悉的 SQL 運算子插入、查詢和管理資料。Amazon Ion 是 JSON 的超集合。Ion 是一種開放原始碼、以文件為基礎的資料格式，可讓您靈活地儲存和處理結構化、半結構化和巢狀資料。

在此步驟中，您可以使用SELECT陳述式從vehicle-registration分類帳中的資料表讀取資料。

警告

當您在沒有索引查詢的情況下在 QLDB 中執行查詢時，它會叫用完整資料表掃描。PartiQL 支援此類查詢，因為它與 SQL 相容。不過，請勿在 QLDB 中執行生產使用案例的資料表掃描。資料表掃描可能會導致大型資料表的效能問題，包括並行衝突和交易逾時。

若要避免資料表掃描，您必須在索引欄位或文件 ID 上使用等式運算子，以WHERE述詞子句執行陳述式；例如， WHERE indexedField = 123或 WHERE indexedField IN (456, 789)。如需詳細資訊，請參閱最佳化查詢效能。

查詢資料表

使用下列程式 (FindVehicles.ts) 來查詢您分類帳中人員下註冊的所有車輛。


/*
 * Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: MIT-0
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

import { QldbDriver, Result, TransactionExecutor } from "amazon-qldb-driver-nodejs";
import { dom } from "ion-js";

import { getQldbDriver } from "./ConnectToLedger";
import { PERSON } from "./model/SampleData";
import { PERSON_TABLE_NAME } from "./qldb/Constants";
import { error, log } from "./qldb/LogUtil";
import { getDocumentId } from "./qldb/Util";
import { prettyPrintResultList } from "./ScanTable";

/**
 * Query 'Vehicle' and 'VehicleRegistration' tables using a unique document ID in one transaction.
 * @param txn The {@linkcode TransactionExecutor} for lambda execute.
 * @param govId The owner's government ID.
 * @returns Promise which fulfills with void.
 */
async function findVehiclesForOwner(txn: TransactionExecutor, govId: string): Promise<void> {
    const documentId: string = await getDocumentId(txn, PERSON_TABLE_NAME, "GovId", govId);
    const query: string = "SELECT Vehicle FROM Vehicle INNER JOIN VehicleRegistration AS r " +
                        "ON Vehicle.VIN = r.VIN WHERE r.Owners.PrimaryOwner.PersonId = ?";

    await txn.execute(query, documentId).then((result: Result) => {
        const resultList: dom.Value[] = result.getResultList();
        log(`List of vehicles for owner with GovId: ${govId}`);
        prettyPrintResultList(resultList);
    });
}

/**
 * Find all vehicles registered under a person.
 * @returns Promise which fulfills with void.
 */
const main = async function(): Promise<void> {
    try {
        const qldbDriver: QldbDriver = getQldbDriver();
        await qldbDriver.executeLambda(async (txn: TransactionExecutor) => {
            await findVehiclesForOwner(txn, PERSON[0].GovId);
        });
    } catch (e) {
        error(`Error getting vehicles for owner: ${e}`);
    }
}

if (require.main === module) {
    main();
}