无法从转换流 nodejs 流式传输对象数组答案

【问题标题】：Not able to stream object array from transform stream nodejs无法从转换流 nodejs 流式传输对象数组
【发布时间】：2022-06-15 14:20:55
【问题描述】：

我正在尝试读取对象数组，将它们转换并写入 Nodejs 中的文件，它给了我错误““块”参数必须是字符串类型或 Buffer 或 Uint8Array 的实例。收到一个实例对象”

我的演示代码：

const readStream = stream.Readable.from(res); // I create stream from array of objects
This is my custom transform stream:
var Transform = stream.Transform;

function Flatten(options) {
  Transform.call(this, options);
};
util.inherits(Flatten, Transform);
Flatten.prototype._transform = function (chunk, enc, cb) {
  
    let obj = chunk;
    let obj2;
    for (let j=0; j<obj.inner.length; j++) {
        let obj1 = obj.inner[j];
        obj2 = {...obj, ...obj1};
        
        delete obj2.inner;
        this.push(new Buffer(obj2));
    }
    
  cb();
};
Then I have a writable stream:
let writeStream = fs.createWriteStream('test1.txt');

Then I pipe all these await pipeline(readStream, tranf, writeStream);
that time I am getting the above error, tried using objectMode: true.

你能帮忙吗

【问题讨论】：

标签： javascript node.js stream nodejs-stream

【解决方案1】：

首先，您需要添加一个选项来处理对象objectMode: true。然后将 Buffer 传递给this.push() 用JSON.stringify 改成字符串

const stream = require('stream');
const fs = require('fs');
const res = [{ inner: [1, 2, 3] }, { inner: [4, 5, 6] }, { inner: [7, 8, 9] }];
const Transform = stream.Transform;

class Flatten extends Transform {
    constructor(options) {
        super(options)
    }

    _transform(chunk, enc, cb) {
        let obj = chunk;
        let obj2;
        for (let j = 0; j < obj.inner.length; j++) {
            let obj1 = obj.inner[j];
            obj2 = { ...obj, ...obj1 };
            delete obj2.inner;
            this.push(JSON.stringify(obj2));
        }
        cb();
    };

};


const readStream = stream.Readable.from(res);
const writeStream = fs.createWriteStream('test1.txt');
const transform = new Flatten({ objectMode: true })

readStream.pipe(transform).pipe(writeStream);

【讨论】：