I'm trying to learn Backbone by looking at an app that someone I know made together with the backbone documentation. The app has a Bucket model and a Company model (i.e. you put companies in the bucket). There's one thing in this bit that I'm unclear about, namely, how it uses the trigger method.
Backbone documentation has this to say about trigger:
trigger object.trigger(event, [*args])
Trigger callbacks for the given event, or space-delimited list of events. Subsequent arguments to trigger will be passed along to the event callbacks.
In the code I'm looking at, trigger is called like this:
this.trigger("add:companies", Companies.get(companyId));
Two questions:
The event I assume is adding a company, but at what point in the code below does that actually happen? Is it when this.set({ "companies": arr }, { silent: true }); is run or when this.save(); is run (or something else)?
If Companies.get(companyId) is the optional argument, what function is it actually passed to?
Excerpt from original code
window.Bucket = Backbone.Model.extend({
defaults: function() {
return {
companies: []
};
},
addCompany: function(companyId) {
var arr = this.get("companies");
arr.push(companyId);
this.set({ "companies": arr }, { silent: true });
this.save();
this.trigger("add:companies", Companies.get(companyId));
},
// ...
The companies property of the bucket is being updated in the addCompany method you describe. An annotated version of your example shows what's taking place:
// 1. get array of companies currently included in the bucket:
var arr = this.get("companies");
// 2. add a company to the array
arr.push(companyId);
// 3. replace the bucket's company list with the array,
// suppressing validation and events:
this.set({"companies": arr}, {silent: true});
// 4. save the bucket:
this.save();
trigger isn't actually affecting the model--it's just a way of letting other pieces of the application know that the company has been added. You could turn around and catch it somewhere else using on with the bucket model:
var bucket = new window.Bucket();
// do stuff
bucket.on('add:companies', function(company) {
alert('a new company has been added to the bucket.');
});
Related
Using React-Redux
I have a select list that when the user chooses one of the options, a item is created and placed in the database (if it matters, the reason its a select box is that there are multiple variations of the same item and what variation is important).
This is working correctly.
My problem is that I am not sure how I can get the id of the new item out of the redux store.
And just for chuckles, the prior developer set all this up with sagas. So I am still coming up to speed on how it all works together.
So when the select box is checked, the function checkFunction is called that calls the function createItem in the saga file. These functions are below:
in Repositories.jsx
checkFunction = (data) => {
const {createItem} = this.props;
// data holds the info that we need to send to the action
const created = createItem(data);
// once data comes back, redirect the user ot the details of the created item
// need id of created item
// navigateTo(`/item-details/${created.id}`);
}
in Repositories.saga.js
export function* createItem(action) {
try {
const {payload: newItem} = action;
// call api to create item
const created = yield call(requestAPI.post, ITEMS_URL, newItem);
// send message that its been done
yield put(actions.repositories.createItem.ok(created));
// send message to refresh item list
yield put(actions.inventories.fetchItems.start());
} catch (e) {
yield put(actions.repositories.createItem.fail(e));
}
}
I don't understand how to return the id of the created item once its created. I feel like I am missing something basic here. Can anyone point me in the right direction?
Actually getting data from saga back to react component is not trivial. There are multiple approaches to do what you need although each has its downside.
1. Call navigateTo in the saga.
export function* createItem(action) {
...
const created = yield call(requestAPI.post, ITEMS_URL, newItem);
yield call(navigateTo, `/item-details/${created.id}`)
}
This would be my recommended solution if you can get the navigateTo function into the saga. Navigation is a side effect and sagas are there to deal with side effects. Make sure to use the call effect, changing the url by directly calling the function can lead to some issues.
2. Store the latest created item id in redux store
In your reducer, when action actions.repositories.createItem.ok(created) is dispatched, store the created item info and then send the latest created item to the component. Finally you can use componentDidUpdate or useEffect to call navigateTo when the prop changes.
render() {
const created = Redux.useSelector(state => state.created);
useEffect(() => navigateTo(`/item-details/${created.id}`), [created])
...
}
This has the disadvantage that the component will rerender becuase of the changed created value.
3. Send callback in the createItem action
You can put a function into your action and then call it from the saga and essentially using it as a callback.
Component:
checkFunction = (data) => {
const {createItem} = this.props;
// data holds the info that we need to send to the action
const created = createItem(data, (created) => {
navigateTo(`/item-details/${created.id}`);
});
}
Saga:
export function* createItem(action) {
...
const created = yield call(requestAPI.post, ITEMS_URL, newItem);
action.callback(created)
...
}
The problem with this approach is that functions are not serializable and so you ideally should avoid them in your actions. Also, technically, there could be multiple sagas handling the same action and then it gets kind of confusing who should call the callback.
In our Single Page Application we've developed a centralized store class that uses an RxJS behavior subject to handle the state of our application and all its mutation. Several components in our application are subscribing to our store's behavior subject in order to receive any update to current application state. This state is then bound to UI so that whenever state changes, UI reflect those changes. Whenever a component wants to change a part of the state, we call a function exposed by our store that does the required work and updates the state calling next on the behavior subject. So far nothing special. (We're using Aurelia as a framework which performs 2 way binding)
The issue we are facing is that as soon as a component changes it's local state variable it receives from the store, other components gets updated even if next() wasn't called on the subejct itself.
We also tried to subscribe on an observable version of the subject since observable are supposed to send a different copy of the data to all subscriber but looks like it's not the case.
Looks like all subject subscriber are receiving a reference of the object stored in the behavior subject.
import { BehaviorSubject, of } from 'rxjs';
const initialState = {
data: {
id: 1,
description: 'initial'
}
}
const subject = new BehaviorSubject(initialState);
const observable = subject.asObservable();
let stateFromSubject; //Result after subscription to subject
let stateFromObservable; //Result after subscription to observable
subject.subscribe((val) => {
console.log(`**Received ${val.data.id} from subject`);
stateFromSubject = val;
});
observable.subscribe((val) => {
console.log(`**Received ${val.data.id} from observable`);
stateFromObservable = val;
});
stateFromSubject.data.id = 2;
// Both stateFromObservable and subject.getValue() now have a id of 2.
// next() wasn't called on the subject but its state got changed anyway
stateFromObservable.data.id = 3;
// Since observable aren't bi-directional I thought this would be a possible solution but same applies and all variable now shows 3
I've made a stackblitz with the code above.
https://stackblitz.com/edit/rxjs-bhkd5n
The only workaround we have so far is to clone the sate in some of our subscriber where we support edition through binding like follow:
observable.subscribe((val) => {
stateFromObservable = JSON.parse(JSON.stringify(val));
});
But this feels more like a hack than a real solution. There must be a better way...
Yes, all subscribers receive the same instance of the object in the behavior subject, that is how behavior subjects work. If you are going to mutate the objects you need to clone them.
I use this function to clone my objects I am going to bind to Angular forms
const clone = obj =>
Array.isArray(obj)
? obj.map(item => clone(item))
: obj instanceof Date
? new Date(obj.getTime())
: obj && typeof obj === 'object'
? Object.getOwnPropertyNames(obj).reduce((o, prop) => {
o[prop] = clone(obj[prop]);
return o;
}, {})
: obj;
So if you have an observable data$ you can create an observable clone$ where subscribers to that observable get a clone that can be mutated without affecting other components.
clone$ = data$.pipe(map(data => clone(data)));
So components that are just displaying data can subscribe to data$ for efficiency and ones that will mutate the data can subscribe to clone$.
Have a read on my library for Angular https://github.com/adriandavidbrand/ngx-rxcache and my article on it https://medium.com/#adrianbrand/angular-state-management-with-rxcache-468a865fc3fb it goes into the need to clone objects so we don't mutate data we bind to forms.
It sounds like the goals of your store are the same as my Angular state management library. It might give you some ideas.
I am not familar with Aurelia or if it has pipes but that clone function is available in the store with exposing my data with a clone$ observable and in the templates with a clone pipe that can be used like
data$ | clone as data
The important part is knowing when to clone and not to clone. You only need to clone if the data is going to be mutated. It would be really inefficient to clone an array of data that is only going to be displayed in a grid.
The only workaround we have so far is to clone the state in some of our subscriber where we support edition through binding like follow:
I don't think I can answer that without rewriting your store.
const initialState = {
data: {
id: 1,
description: 'initial'
}
}
That state object has deeply structured data. Everytime you need to mutate the state the object needs to be reconstructed.
Alternatively,
const initialState = {
1: {id: 1, description: 'initial'},
2: {id: 2, description: 'initial'},
3: {id: 3, description: 'initial'},
_index: [1, 2, 3]
};
That is about as deep of a state object that I would create. Use a key/value pair to map between IDs and the object values. You can now write selectors easily.
function getById(id: number): Observable<any> {
return subject.pipe(
map(state => state[id]),
distinctUntilChanged()
);
}
function getIds(): Observable<number[]> {
return subject.pipe(
map(state => state._index),
distinctUntilChanged()
);
}
When you want change a data object. You have to reconstruct the state and also set the data.
function append(data: Object) {
const state = subject.value;
subject.next({...state, [data.id]: Object.freeze(data), _index: [...state._index, data.id]});
}
function remove(id: number) {
const state = {...subject.value};
delete state[id];
subject.next({...state, _index: state._index.filter(x => x !== id)});
}
Once you have that done. You should freeze downstream consumers of your state object.
const subject = new BehaviorSubject(initialState);
function getStore(): Observable<any> {
return subject.pipe(
map(obj => Object.freeze(obj))
);
}
function getById(id: number): Observable<any> {
return getStore().pipe(
map(state => state[id]),
distinctUntilChanged()
);
}
function getIds(): Observable<number[]> {
return getStore().pipe(
map(state => state._index),
distinctUntilChanged()
);
}
Later when you do something like this:
stateFromSubject.data.id = 2;
You'll get a run-time error.
FYI: The above is written in TypeScript
The big logical issue with your example is that the object forwarded by the subject is actually a single object reference. RxJS doesn't do anything out of the box to create clones for you, and that is fine otherwise it would result in unnecessary operations by default if they aren't needed.
So while you can clone the value received by the subscribers, you're still not save for access of BehaviorSubject.getValue(), which would return the original reference. Besides that having same refs for parts of your state is actually beneficial in lots of ways as e.g arrays can be re-used for multiple displaying components vs having to rebuild them from scratch.
What you want to do instead is to leverage a single-source-of-truth pattern, similar to Redux, where instead of making sure that subscribers get clones, you're treating your state as immutable object. That means every modification results in a new state. That further means you should restrict modifications to actions, (actions + reducers in Redux) which construct a new state of the current plus the necessary changes and return the new copy.
Now all of that might sound like a lot of work but you should take a look at the official Aurelia Store Plugin, which is sharing pretty much the same concept as you have plus making sure that best ideas of Redux are brought over to the world of Aurelia.
Collaboration Mode:
What is the best way to propagate changes from Client #1's canvas to client #2's canvas? Here's how I capture and send events to Socket.io.
$scope.canvas.on('object:modified',function(e) {
Socket.whiteboardMessage({
eventId:'object:modified',
event:e.target.toJSON()
});
});
On the receiver side, this code works splendidly for adding new objects to the screen, but I could not find documentation on how to select and update an existing object in the canvas.
fabric.util.enlivenObjects([e.event], function(objects) {
objects.forEach(function(o) {
$scope.canvas.add(o);
});
});
I did see that Objects have individual setters and one bulk setter, but I could not figure out how to select an existing object based on the event data.
Ideally, the flow would be:
Receive event with targeted object data.
Select the existing object in the canvas.
Perform bulk update.
Refresh canvas.
Hopefully someone with Fabric.JS experience can help me figure this out. Thanks!
UPDATED ANSWER - Thanks AJM!
AJM was correct in suggesting a unique ID for every newly created element. I was also able to create a new ID for all newly created drawing paths as well. Here's how it worked:
var t = new fabric.IText('Edit me...', {
left: $scope.width/2-100,
top: $scope.height/2-50
});
t.set('id',randomHash());
$scope.canvas.add(t);
I also captured newly created paths and added an id:
$scope.canvas.on('path:created',function(e) {
if (e.target.id === undefined) {
e.target.set('id',randomHash());
}
});
However, I encountered an issue where my ID was visible in console log, but it was not present after executing object.toJSON(). This is because Fabric has its own serialization method which trims down the data to a standardized list of properties. To include additional properties, I had to serialize the data for transport like so:
$scope.canvas.on('object:modified',function(e) {
Socket.whiteboardMessage({
object:e.target.toJSON(['id']) // includes "id" in output.
})
});
Now each object has a unique ID with which to perform updates. On the receiver's side of my code, I added AJM's object-lookup function. I placed this code in the "startup" section of my application so it would only run once (after Fabric.js is loaded, of course!)
fabric.Canvas.prototype.getObjectById = function (id) {
var objs = this.getObjects();
for (var i = 0, len = objs.length; i < len; i++) {
if (objs[i].id == id) {
return objs[i];
}
}
return 0;
};
Now, whenever a new socket.io message is received with whiteboard data, I am able to find it in the canvas via this line:
var obj = $scope.canvas.getObjectById(e.object.id);
Inserting and removing are easy, but for updating, this final piece of code did the trick:
obj.set(e.object); // Updates properties
$scope.canvas.renderAll(); // Redraws canvas
$scope.canvas.calcOffset(); // Updates offsets
All of this required me to handle the following events. Paths are treated as objects once they're created.
$scope.canvas.on('object:added',function(e) { });
$scope.canvas.on('object:modified',function(e) { });
$scope.canvas.on('object:moving',function(e) { });
$scope.canvas.on('object:removed',function(e) { });
$scope.canvas.on('path:created',function(e) { });
I did something similar involving a single shared canvas between multiple users and ran into this exact issue.
To solve this problem, I added unique IDs (using a javascript UUID generator) to each object added to the canvas (in my case, there could be many users working on a canvas at a time, thus I needed to avoid collisions; in your case, something simpler could work).
Fabric objects' set method will let you add an arbitrary property, like an id: o.set('id', yourid). Before you add() a new Fabric object to your canvas (and send that across the wire), tack on an ID property. Now, you'll have a unique key by which you can pick out individual objects.
From there, you'd need a method to retrieve an object by ID. Here's what I used:
fabric.Canvas.prototype.getObjectById = function (id) {
var objs = this.getObjects();
for (var i = 0, len = objs.length; i < len; i++) {
if (objs[i].id == id) {
return objs[i];
}
}
return null;
};
When you receive data from your socket, grab that object from the canvas by ID and mutate it using the appropriate set methods or copying properties wholesale (or, if getObjectById returns null, create it).
I'm facing a "change event not firing" issue on Backbone.js =/
Here my view of User model :
window.UserView = Backbone.View.extend({
...
initialize: function()
{
this.model.on('destroy', this.remove, this);
this.model.on('change', function()
{
console.log('foo');
});
},
render: function(selected)
{
var view = this.template(this.model.toJSON());
$(this.el).html(view);
return this;
},
transfer: function(e)
{
var cas = listofcas;
var transferTo = Users.getByCid('c1');
var transferToCas = transferTo.get('cas');
this.model.set('cas', cas);
console.log('current model');
console.log(this.model);
//this.model.change();
this.model.trigger("change:cas");
console.log('trigger change');
transferTo.set('cas', transferToCas);
console.log('transferto model');
console.log(transferTo);
//transferTo.change();
transferTo.trigger("change:cas");
console.log('trigger change');
}
});
Here, the User model :
window.User = Backbone.Model.extend({
urlRoot: $('#pilote-manager-app').attr('data-src'),
initialize: function()
{
this.set('rand', 1);
this.set('specialite', this.get('sfGuardUser').specialite);
this.set('name', this.get('sfGuardUser').first_name + ' ' + this.get('sfGuardUser').last_name);
this.set('userid', this.get('sfGuardUser').id);
this.set('avatarsrc', this.get('sfGuardUser').avatarsrc);
this.set('cas', new Array());
if (undefined != this.get('sfGuardUser').SignalisationBouclePorteur) {
var cas = new Array();
_.each(this.get('sfGuardUser').SignalisationBouclePorteur, function(value)
{
cas.push(value.Signalisation);
});
this.set('cas', cas);
}
}
});
In User model, there is "cas" attribute, which is an array of objects.
I read in others topics that change events are not fire on model.set if attributes are not a value.
So, I try to trigger directly the change event with model.change() method.
But, I have no "foo" log in my console ...
I'm pretty new to backbone and I was having this same problem.
After doing some research, I found a few posts that shed a little bit more light on why this was happening, and eventually things started to make sense:
Question 1
Question 2
The core reason has to do with the notion of reference equality versus set/member equality. It appears that to a large extent, reference equality is one of the primary techniques backbone uses to figure out when an attribute has changed.
I find that if I use techniques that generate a new reference like Array.slice() or _.clone(), the change event is recognized.
So for example, the following code does not trigger the event because I'm altering the same array reference:
this.collection.each(function (caseFileModel) {
var labelArray = caseFileModel.get("labels");
labelArray.push({ Key: 1, DisplayValue: messageData });
caseFileModel.set({ "labels": labelArray });
});
While this code does trigger the event:
this.collection.each(function (caseFileModel) {
var labelArray = _.clone(caseFileModel.get("labels")); // The clone() call ensures we get a new array reference - a requirement for the change event
labelArray.push({ Key: 1, DisplayValue: messageData });
caseFileModel.set({ "labels": labelArray });
});
NOTE: According to the Underscore API, _.clone() copies certain nested items by reference. The root/parent object is cloned though, so it will work fine for backbone. That is, if your array is very simple and does not have nested structures e.g. [1, 2, 3].
While my improved code above triggered the change event, the following did not because my array contained nested objects:
var labelArray = _.clone(this.model.get("labels"));
_.each(labelArray, function (label) {
label.isSelected = (_.isEqual(label, selectedLabel));
});
this.model.set({ "labels": labelArray });
Now why does this matter? After debugging very carefully, I noticed that in my iterator I was referencing the same object reference backbone was storing. In other words, I had inadvertently reached into the innards of my model and flipped a bit. When I called setLabels(), backbone correctly recognized that nothing changed because it already knew I flipped that bit.
After looking around some more, people seem to generally say that deep copy operations in javascript are a real pain - nothing built-in to do it. So I did this, which worked fine for me - general applicability may vary:
var labelArray = JSON.parse(JSON.stringify(this.model.get("labels")));
_.each(labelArray, function (label) {
label.isSelected = (_.isEqual(label, selectedLabel));
});
this.model.set({ "labels": labelArray });
Interesting. I would have thought that .set({cas:someArray}) would have fired off a change event. Like you said, it doesn't seem to, and I can't get it to fire with .change() BUT, I can get the events to work if I just do model.trigger('change') or model.trigger('change:attribute')
This would allow you to trigger the change event without that random attribute hack.
If someone could explain what is going on with events, Backbone, and this code, that would help me learn something too... Here is some code.
Ship = Backbone.Model.extend({
defaults: {
name:'titanic',
cas: new Array()
},
initialize: function() {
this.on('change:cas', this.notify, this);
this.on('change', this.notifyGeneral, this);
},
notify: function() {
console.log('cas changed');
},
notifyGeneral: function() {
console.log('general change');
}
});
myShip = new Ship();
myShip.set('cas',new Array());
// No event fired off
myShip.set({cas: [1,2,3]}); // <- Why? Compared to next "Why?", why does this work?
// cas changed
// general change
myArray = new Array();
myArray.push(4,5,6);
myShip.set({cas:myArray}); // <- Why?
// No event fired off
myShip.toJSON();
// Array[3] is definitely there
myShip.change();
// No event fired off
The interesting part that might help you:
myShip.trigger('change');
// general change
myShip.trigger('change:cas');
// cas changed
I find this interesting and I hope this answer will also spawn some insightful explanation in comments which I don't have.
I need to search the CouchDB based on several criteria entered in a form. Name, an array of Tags and so on. I would then need various views to index on these fields. Ultimately, all the results will be collated in data.js and provided to mustache.html. Say there are 3 views - docsByName, docsByTags, docsById.
What I don't know is, how to query all these views in query.js. Can this be done and how ?
Or should the approach be of that to write one view that makes multiple emits for each search somehow ?
Thank you.
From what you say I assume you are using Evently, so I will quote from Evently primer:
The async function is the main star, which in this case makes an Ajax request (but it can do anything it wants). Another important thing to note is that the first argument to the async function is a callback which you use to tell Evently when you are done with your asynchronous action. [...] Whatever you pass to the callback function then becomes the first item passed to the data function.
In short: put your Ajax requests in async.js.
As a side note: Evently is only one of the possible choices to write a couchapp and it is not clear if it is maintained. However it works and it is easy to rearrange the code to not use it.
EDIT: here is a sample async function (cut&paste from an old program):
function(cb, e) {
var app = $$(this).app
;
app.db.openDoc('SOMEDOCID', {
error: function(code, error, reason) {
alert("Error("+code+" "+error+"): "+reason);
}
, success: function(doc) {
app.view('SOMEVIEWNAME', {
include_docs: true
, error: function(code, error, reason) {
alert("Error("+code+" "+error+"): "+reason);
}
, success: function(resp) {
resp.doc = doc;
cb(resp);
}
});
}
});
}