How to Automatically Download attachments from opportunity?

Hi Tanu,

You can achieve this by Creating a javascript custom button on opportunity and apex class. Here is the code

Apex Class

global class DisableInputTextCntrl {

public static List<String> downloadUrlList;
public static List<Attachment> attachmentList;

webservice static List<String> download(String oppId){

downloadUrlList = new List<String>();
attachmentList = [select id from attachment where ParentId =:oppId];

if(!attachmentList.isEmpty()){
for(Attachment attach : attachmentList){
String url = '/servlet/servlet.FileDownload?file='+string.valueOf(attach.id);
downloadUrlList.add(url);
}
}

return downloadUrlList;
}
}

Custom Button Code

{!REQUIRESCRIPT("/soap/ajax/15.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/15.0/apex.js")}

(function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.multiDownload = f()}})(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){
'use strict';

function fallback(urls) {
var i = 0;

(function createIframe() {
var frame = document.createElement('iframe');
frame.style.display = 'none';
frame.src = urls[i++];
document.documentElement.appendChild(frame);

// the download init has to be sequential otherwise IE only use the first
var interval = setInterval(function () {
if (frame.contentWindow.document.readyState === 'complete') {
clearInterval(interval);

// Safari needs a timeout
setTimeout(function () {
frame.parentNode.removeChild(frame);
}, 1000);

if (i < urls.length) {
createIframe();
}
}
}, 100);
})();
}

function isFirefox() {
// sad panda 🙁
return /Firefox\//i.test(navigator.userAgent);
}

function sameDomain(url) {
var a = document.createElement('a');
a.href = url;

return location.hostname === a.hostname && location.protocol === a.protocol;
}

function download(url) {
var a = document.createElement('a');
a.download = '';
a.href = url;
// firefox doesn't support `a.click()`...
a.dispatchEvent(new MouseEvent('click'));
}

module.exports = function (urls) {
if (!urls) {
throw new Error('`urls` required');
}

if (typeof document.createElement('a').download === 'undefined') {
return fallback(urls);
}

var delay = 0;

urls.forEach(function (url) {
// the download init has to be sequential for firefox if the urls are not on the same domain
if (isFirefox() && !sameDomain(url)) {
return setTimeout(download.bind(null, url), 100 * ++delay);
}

download(url);
});
}

},{}]},{},[1])(1)
});

(function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.multiDownload = f()}})(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){
'use strict';

function fallback(urls) {
var i = 0;

(function createIframe() {
var frame = document.createElement('iframe');
frame.style.display = 'none';
frame.src = urls[i++];
document.documentElement.appendChild(frame);

// the download init has to be sequential otherwise IE only use the first
var interval = setInterval(function () {
if (frame.contentWindow.document.readyState === 'complete') {
clearInterval(interval);

// Safari needs a timeout
setTimeout(function () {
frame.parentNode.removeChild(frame);
}, 1000);

if (i < urls.length) {
createIframe();
}
}
}, 100);
})();
}

function isFirefox() {
// sad panda 🙁
return /Firefox\//i.test(navigator.userAgent);
}

function sameDomain(url) {
var a = document.createElement('a');
a.href = url;

return location.hostname === a.hostname && location.protocol === a.protocol;
}

function download(url) {
var a = document.createElement('a');
a.download = '';
a.href = url;
// firefox doesn't support `a.click()`...
a.dispatchEvent(new MouseEvent('click'));
}

module.exports = function (urls) {
if (!urls) {
throw new Error('`urls` required');
}

if (typeof document.createElement('a').download === 'undefined') {
return fallback(urls);
}

var delay = 0;

urls.forEach(function (url) {
// the download init has to be sequential for firefox if the urls are not on the same domain
if (isFirefox() && !sameDomain(url)) {
return setTimeout(download.bind(null, url), 100 * ++delay);
}

download(url);
});
}

},{}]},{},[1])(1)
});

var Id = '{!Opportunity.Id}';
var arrayId = [];
arrayId = sforce.apex.execute("DisableInputTextCntrl","download",{oppId:Id});

if(arrayId.length > 0){
multiDownload(arrayId);
}