从存储到流：将 MongoDB 数据直接交付给用户

步骤 1：MongoDB 游标

以下是我们设置光标的方法（重复使用您的代码片段）：

const cursor =
    userObject?.data?.serviceProviderName === 'ZYRO'
        ? zyroTransactionModel.find(query).cursor()
        : finoTransactionModel.find(query).cursor();

console.log("Cursor created successfully");

步骤2：设置ZIP文件

使用 yazl 库将 CSV 数据传输到 ZIP 文件中：

const yazl = require('yazl');
const zipfile = new yazl.ZipFile();

reply.raw.writeHead(200, {
    "Content-Type": "application/zip",
    "Content-Disposition": "attachment; filename=transactions.zip",
});

zipfile.outputStream.pipe(reply.raw);

const cleanup = async () => {
    console.log("Cleaning up resources...");
    zipfile.end(); // Finalize ZIP
    await cursor.close();
};
reply.raw.on("close", cleanup);
reply.raw.on("error", cleanup);

步骤 3：创建动态 CSV 流

动态生成 CSV 数据并将其流式传输到 ZIP 文件中：

const createNewCSVStream = (headers) => {
    const csvStream = new Readable({ read() {} });
    csvStream.push(headers.join(",") + "\n"); // Add headers
    return csvStream;
};

const filteredHeaders = getHeaders(transactionDownloadFields, userObject?.state?.auth?.role);
const currentCSVStream = createNewCSVStream(filteredHeaders);

zipfile.addReadStream(currentCSVStream, "transactions_part_1.csv");

步骤 4：将 MongoDB 数据传输到 CSV

将 MongoDB 中的数据直接流式传输到 CSV：

cursor.on('data', (doc) => {
    const csvRow = filteredHeaders.map(header => doc[header.key] || '').join(',');
    currentCSVStream.push(csvRow + '\n'); // Write row
});

cursor.on('end', () => {
    currentCSVStream.push(null); // End the stream
    zipfile.end(); // Finalize the ZIP
});

步骤5：处理来自MongoDB游标的数据

从 MongoDB 游标流式传输文档，根据需要对其进行转换，并动态地将行写入 CSV 流：

try {
    for await (const doc of cursor) {
        if (clientDisconnected) {
            console.log("Client disconnected. Stopping processing...");
            break;
        }

        streamedCount++;
        rowCount++;

        let row = "";
        const filteredHeaders = getHeaders(
            transactionDownloadFields,
            userObject?.state?.auth?.role
        );

        for (let i = 0; i < filteredHeaders.length; i++) {
            const field = filteredHeaders[i];

            // Fetch the corresponding field configuration from transactionDownloadFields
            const originalField = transactionDownloadFields.find((f) => f.value === field.value);

            // Get the value from the transaction document
            let value = getValueFromTransaction(doc, field.value);

            // Apply transformation if the field has a transform function
            if (originalField?.transform) {
                value = originalField.transform(value);
            }

            // Enclose the value in double quotes
            value = value !== undefined ? `"${value}"` : '"N/A"';
            row += (i > 0 ? "," : "") + value;
        }
        row += "\n";
        currentCSVStream.push(row);

        // Check if the row count has reached the threshold for the current CSV file
        if (rowCount >= MAX_ROWS_PER_FILE) {
            console.log(`Threshold reached for file ${fileIndex - 1}. Starting new file...`);
            currentCSVStream.push(null); // End the current CSV stream
            currentCSVStream = createNewCSVStream(); // Start a new stream
            rowCount = 0; // Reset the row count
        }
    }

    // Finalize the current CSV stream if it has data
    if (currentCSVStream) {
        currentCSVStream.push(null);
    }

    // Finalize the ZIP file
    zipfile.end();
    console.log(`Successfully streamed ${streamedCount} rows across ${fileIndex - 1} files.`);
} catch (error) {
    console.error("Error during processing:", error);
    if (!headersSent) reply.status(500).send({ error: "Failed to generate ZIP file" });
} finally {
    // Cleanup: Close the MongoDB cursor
    await cursor.close().catch((err) => console.error("Error closing cursor:", err));
}

概括

使用 for await...of 进行文档迭代：

高效地从 MongoDB 游标中逐个流式传输文档。

无需将所有数据加载到内存中即可实现实时处理。

通过迭代filteredHeaders来动态构造每一行。

如果在 transactionDownloadFields 中定义，则使用转换函数应用转换。

行阈值和文件拆分：

监控行数是否超过阈值 (MAX_ROWS_PER_FILE)。

达到阈值时结束当前 CSV 流并启动新的 CSV 流。

如果处理过程中出现问题，则记录并发送错误响应。

通过在 finally 块中关闭 MongoDB 游标来确保正确清理。

推送 null 来终止当前 CSV 流。

处理完所有行后，完成 ZIP 文件。