MongoDB学习笔记之GridFS使用介绍

什么是GridFS

GridFS 是 MongoDB 提供的一种协议，用于存储可扩展的大型二进制数据文件，例如图像、音频和视频文件。MongoDB 的文件系统使用两个集合来存储二进制文件，使之可以分批读取或者分片存储。

如何使用GridFS

1. 创建GridFS对象

创建GridFSBucket对象时，必须指定数据库名称和集合名称，例如：

const { MongoClient } = require('mongodb');
const { GridFSBucket } = require('mongodb');

const uri = "mongodb+srv://<username>:<password>@cluster0.mongodb.net/test?retryWrites=true&w=majority";
const client = new MongoClient(uri);

async function run() {
    try {
        await client.connect();
        console.log("Connected correctly to server");

        const database = client.db('<database name>');
        const bucket = new GridFSBucket(database, { bucketName: '<bucket name>' });

    } catch (err) {
        console.log(err.stack);
    }

    // Close the connection to the MongoDB server
    await client.close();
}

run().catch(console.dir);

在该示例中，<username>、<password>、<database name> 和 <bucket name> 需要替换为实际值。

1. 存储文件

使用openUploadStream方法上传文件，例如：

const { ObjectId } = require('mongodb');
const fs = require('fs');

// An error will be thrown if the file does not exist
const readableStream = fs.createReadStream('<path to file>');
const uploadStream = bucket.openUploadStream('<filename>');

// Store custom metadata with the file
const metadata = { owner: "username", readPrivilege: true };
uploadStream.on('finish', function() {
    console.log('File uploaded!')
    console.log(`File ID: ${uploadStream.id}`);
});

// Pipe the file data to the GridFS file object
readableStream.pipe(uploadStream);

在该示例中，<path to file> 和 <filename> 需要替换为实际值。上传文件时可以选择存储自定义的文件元数据（例如上传者信息等）。

1. 下载文件

使用openDownloadStream方法下载文件，例如：

const downloadStream = bucket.openDownloadStream(ObjectId('<file ID>'));

// Pipe the file data to the response object
downloadStream.pipe(response);

在该示例中，<file ID> 需要替换为实际值。下载文件时可以将文件数据直接发送到响应对象，以便实现断点续传等功能。

示例说明

1. 上传文件

const { MongoClient } = require('mongodb');
const { GridFSBucket } = require('mongodb');
const fs = require('fs');

const uri = "mongodb+srv://<username>:<password>@cluster0.mongodb.net/test?retryWrites=true&w=majority";
const client = new MongoClient(uri);

async function run() {
    try {
        await client.connect();
        console.log("Connected correctly to server");

        const database = client.db('<database name>');
        const bucket = new GridFSBucket(database, { bucketName: '<bucket name>' });

        const readableStream = fs.createReadStream('<path to file>');
        const uploadStream = bucket.openUploadStream('<filename>');

        const metadata = { owner: "username", readPrivilege: true };
        uploadStream.on('finish', function() {
            console.log('File uploaded!')
            console.log(`File ID: ${uploadStream.id}`);
        });

        readableStream.pipe(uploadStream);

    } catch (err) {
        console.log(err.stack);
    }

    await client.close();
}

run().catch(console.dir);

在该示例中，替换 <username>、<password>、<database name>、<bucket name>、<path to file> 和 <filename> 为实际值。运行该脚本后，将会上传指定路径下的文件到 GridFS，并打印出文件 ID。

1. 下载文件

const { MongoClient } = require('mongodb');
const { GridFSBucket } = require('mongodb');
const fs = require('fs');

const uri = "mongodb+srv://<username>:<password>@cluster0.mongodb.net/test?retryWrites=true&w=majority";
const client = new MongoClient(uri);

async function run() {
    try {
        await client.connect();
        console.log("Connected correctly to server");

        const database = client.db('<database name>');
        const bucket = new GridFSBucket(database, { bucketName: '<bucket name>' });

        const downloadStream = bucket.openDownloadStream(ObjectId('<file ID>'));

        downloadStream.pipe(fs.createWriteStream('<path to output>'));

    } catch (err) {
        console.log(err.stack);
    }

    await client.close();
}

run().catch(console.dir);

在该示例中，替换 <username>、<password>、<database name>、<bucket name>、<file ID> 和 <path to output> 为实际值。运行该脚本后，将会下载指定 ID 的文件，并保存到指定路径下。