update, instead of replace, list used for ng-repeat - javascript

How it is
I have an array of objects called vm.queued_messages (vm is set to this in my controller), and vm.queued_messages is used in ng-repeat to display a list of div's.
When I make an API call which changes the underlying model in the database, I have the API call return a fresh list of queued messages, and in my controller I set the variable vm.queued_messages to that new value, that fresh list of queued messages.
vm.queued_messages = data; // data is the full list of new message objects
The problem
This "full replacement" of vm.queued_messages worked exactly as I wanted, at first. But what I didn't think about was the fact that even objects in that list which had no changes to any properties were leaving and new objects were taking their place. This made no different to the display because the new objects had identical keys and values, they were technically different objects, and thus the div's were secretly leaving and entering every time. THIS MEANS THERE ARE MANY UNWANTED .ng-enter's AND .ng-leave's OCCURRING, which came to my attention when I tried to apply an animation to these div's when they entered or left. I would expect a single div to do the .ng-leave animation on some click, but suddenly a bunch of them did!
My solution attempt
I made a function softRefreshObjectList which updates the keys and values (as well as any entirely new objects, or now absent objects) of an existing list to match those of a new list, WITHOUT REPLACING THE OBJECTS, AS TO MAINTAIN THEIR IDENTITY. I matched objects between the new list and old list by their _id field.
softRefreshObjectList: function(oldObjs, newObjs) {
var resultingObjList = [];
var oldObjsIdMap = {};
_.each(oldObjs, function(obj) {
oldObjsIdMap[obj._id] = obj;
});
_.each(newObjs, function(newObj) {
var correspondingOldObj = oldObjsIdMap[newObj._id];
if (correspondingOldObj) {
// clear out the old obj and put in the keys/values from the new obj
for (var key in correspondingOldObj) delete correspondingOldObj[key];
for (var key in newObj) correspondingOldObj[key] = newObj[key];
resultingObjList.push(correspondingOldObj);
} else {
resultingObjList.push(newObj);
};
});
return resultingObjList;
}
which works for certain things, but with other ng-repeat lists I get odd behavior, I believe because of the delete's and values of the objects being references to other controller variables. Before continuing down this rabbit hole, I want to make this post in case I'm thinking about this wrong, or there's something I'm missing.
My question
Is there a more appropriate way to handle this case, which would either make it easier to handle, or bypass my issue altogether?
Perhaps a way to signal to Angular that these objects are identified by their _id instead of their reference, so that it doesn't make them leave and enter as long as the _id doesn't change.
Or perhaps a better softRefreshObjectList function which iterates through the objects differently, if there's something fishy about how I'm doing it.

Thanks to Petr's comment, I now know about track by for ng-repeat. It's where you can specify a field in your elements that "identifies" that element, so that angular can know when that element really is leaving or entering. In my case, that field was _id, and adding track by message._id to my ng-repeat (ng-repeat="message in ctrl.queued_messages track by message._id") solved my issue perfectly.
Docs here. Search for track by.

Related

How can I overwrite an array using Ractive?

I have a componet that updates an array on it's parent. Specifically, it takes additions, and creates an entirely new array that has been sorted, overwriting the original array.
var sortedUpdatedDomainNames = updatedProposedDomainNames.sort(sorts.domainName)
// even though we sort them, after setting the value, getting it returns the unsorted items
debugger;
Typing in the debugger here:
sortedUpdatedDomainNames
(4) ["example.com", "www.example.com", "swag.com", "www.swag.com"]
OK that works. The array items are sorted (using sorts.domainName which puts www immediately after parent domains)
await parentComponent.set('order.proposedDomainNames', sortedUpdatedDomainNames)
Here's the first issue: the DOM doesn't update poroperly, some items are duplicated in the DOM even though they're not duplicated in the data.
Running parentComponent.update fixes these duplications, however:
// Work around odd ractive bug where DOM doesn't update properly
// Trigger an update manually using .update()
// TODO: find proper fix!
await parentComponent.update('order.proposedDomainNames');
Her's the second issue: the values are now unsorted (well, they're sorted alphabetically now, which isn't what I want).
parentComponent.get('order.proposedDomainNames');
(4) ["example.com", "swag.com", "www.example.com", "www.swag.com"]
How can I overwrite an array using Ractive?
Please do not submit answers re: ractive.splice() etc - I do not know in advance the index where the data will be inserted, I simply wish to sort the entire array and update it.
Using the deep option for ractive.set() ensures the DOM updates to match the new array values - even though the array is a simple array of primitives.
await parentComponent.set('order.proposedDomainNames', sortedUpdatedDomainNames, { deep: true })
I also tried shuffle, which was suggested, but this does not work and the DOM is still inconsistent with the array value when using shuffle.
Though the issue is solved, I'm still interested in why deep was needed to make the DOM update correctly, so if you have your own answer to that, add it and I'l; accept it!

Remove all elements within a ng-repeat in Angular

I'm working with Angular and part of my page utilizes ng-repeat to display some bug tracker tickets. As part of the site, I also want to provide the ability to search tickets. I'm able to get that part working as I want, and if I'm just appending new tickets they show up fine.
However I would like to be able to, if a user searches, delete all of the currently visible ticket divs and replace them with the search results.
My initial thinking, since I have the ng-repeat set as item in tickets track by item.id, was to just set $scope.tickets equal to the new data. However, this didn't cause Angular to update the DOM.
So, I tried setting $scope.tickets equal to an empty array and then setting it equal to the new data:
$scope.$apply(function() {
$scope.tickets = [];
$scope.tickets = data;
});
Still no update to the DOM, even though console.log($scope.tickets) shows the correct objects.
I'm aware of the method of
$scope.$apply(function() {
array.splice(index, 1);
});
to remove individual elements, but I'm not sure how I would apply that removing all of the elements.
I'll try and get a Plunkr or JSBin added to the Q soon.
What would be the proper way for me to make Angular replace all of the current elements with the new elements created from the data?
try setting array.length = 0
this deletes all elements, while not removing the reference to the array, which actually seems to be the problem in your case.
but another way would be to have a additional data bag.
for example have $scope.data.tickets then you can reasign tickets as usual. important thing is, you have to reference your items using item in data.tickets
Did you test $watch?
$scope.$watch('tickets', function() {
// update data HERE
});

With Backbone.js, how to Bind to an array's changes w/o needing to manually trigger?

I'm creating an invitation dialog that allows users to enter emails. Currently in the model I am creating an array to hold the emails:
initialize : function() {
this.model.set({
invite_email_array : new Array()
});
}
And then I'm adding/removing items in the view like so:
this.model.get('invite_email_array').push('email#domain.com');
Then problem is the binder is not being triggered when I either add or remove an email from the model. Here is my binder:
binder : function() {
model.on("change:invite_email_array", onInviteEmailArrayChange() )
}
The only way I was able to get the binding to trigger was to trigger it manually when I make updates.. an ugly hack
this.model.trigger("change:invite_email_array");
Any suggestions on a better way to maintain a list of emails and then be able to bind to the object on add/removes?
Thanks
In the example you give, you're bypassing set by altering the array directly. In order to trigger the change, you would need to set the altered array after pushing the new e-mail. Something to the effect of:
var arr = _.clone(this.model.get('invite_email_array'));
arr.push('email#domain.com');
this.model.set({ invite_email_array: arr });
As soon as you've introduced an array, however, it may be worth considering whether the view's design is really reflecting its intent. Collections (or arrays) of anything often signal that it's time to consider simplifying models or views. Even though a single e-mail seems too trivial assign to its own view/model, it may make sense to track an array of e-mails as a collection of "invitation" views and watch for changes accordingly.

Backbone multi-collection global search

I'm playing around with the idea of creating a global search that allows me to find any model in any of a number of collections by any of the model's attributes. For example:
I have the following collections:
Users
Applications
Roles
I don't know ahead of time what attributes each User, Applicaion and Role will have but for illustration purposes lets say I have:
User.name
User.last_name
User.email
Application.title
Application.description
Role.name
Role.description
Now, lets say I create a model called Site with a method called search. I want Site.search(term) to search through all the items in each collection where term matches any of the attributes. In essence, a global model search.
How would you suggest I approach this? I can brute-force it by iterating through all the collections' models and each model's attributes but that seems bloated and inefficient.
Any suggestions?
/// A few minutes later...
Here's a bit of code I tried just now:
find: function(query) {
var results = {}; // variable to hold the results
// iterate over the collections
_.each(["users", "applications", "roles"], _.bind(function(collection){
// I want the result to be grouped by type of model so I add arrays to the results object
if ( !_.isUndefined(results[collection]) || !_.isArray(results[collection]) ) {
results[collection] = [];
}
// iterate over the collection's models
_.each(this.get(collection).models, function(model){
// iterate over each model's attributes
_.each(model.attributes, function(value){
// for now I'm only considering string searches
if (_.isString(value)) {
// see if `query` is in the attribute's string/value
if (value.indexOf(query) > -1) {
// if so, push it into the result's collection arrray
results[collection].push(model);
}
};
});
});
// a little cleanup
results[collection] = _.compact(results[collection]);
// remove empty arrays
if (results[collection].length < 1) {
delete results[collection];
}
},this));
// return the results
return results;
}
This yields the expected result and I suppose it works fine but it bothers me that I'm iterating over three arrays. there may not be another solution but I have a feeling there is. If anyone can suggest one, thank you! Meanwhile I'll keep researching.
Thank you!
I would strongly discourage you from doing this, unless you have a very limited set of data and performance is not really a problem for you.
Iteration over everything is a no-no if you want to perform search. Search engines index data and make the process feasible. It is hard to build search, and there is no client-side library that does that effectively.
Which is why everybody is doing searching on the server. There exist easy (or sort of) to use search engines such as solr or the more recent and my personal preference elasticsearch. Presumably you already store your models/collections on the server, it should be trivial to also index them. Then searching becomes a question of making a REST call from your client.

KnockoutJS: Update/Insert data to a viewModel using mapping

I've been trying to figure this out for quite some time now. I couldn't find anything that addresses this problem, but please correct me if I'm wrong.
The problem:
I have data from a JSON API comming in, with an nested array/object structure. I use mapping to initially fill the model with my data. To update this, I want to extend the model if new data arrives, or update the existing data.
As far as I found out, the mapping option key, should do this trick for me, but I might have misunderstood the functionality of the mapping options.
I've boiled down the problem to be represented by this example:
var userMapping = {
key: function(item) {
return ko.utils.unwrapObservable(item.id);
}
};
// JSON call replaced with values
var viewModel = {
users: ko.mapping.fromJS([], userMapping)
};
// Should insert new - new ID?
ko.mapping.fromJS([{"id":1,"name":"Foo"}, {"id":2,"name":"Bar"}], userMapping, viewModel.users);
// Should only update ID#1 - same ID?
ko.mapping.fromJS([{"id":1,"name":"Bat"}], userMapping, viewModel.users);
// Should insert new - New ID?
ko.mapping.fromJS([{"id":3,"name":"New"}, {"id":4,"name":"New"}], userMapping, viewModel.users);
ko.applyBindings(viewModel);​
Fiddle: http://jsfiddle.net/mikaelbr/gDjA7/
As you can see, the first line inserts the data. All good. But when I try to update, it replaces the content. The same for the third mapping; it replaces the content, instead of extening it.
Am I using it wrong? Should I try to extend the content "manually" before using mapping?
Edit Solution:
I solved this case by having a second helper array storing all current models. On new data i extended this array, and updated the view model to contain the accumulated items.
On update (In my case a WebSocket message), I looped through the models, changed the contents of the item in question, and used method valueHasMutated() to give notice of changed value to the Knockout lib.
From looking at your example code the mapping plugin is behaving exactly as I would expect it to. When you call fromJS on a collection you are effectively telling the mapping plugin this is the new contents of that collection. For example:
On the second line, How could it know whether you were updating or whether you had simply removed id:2?
I can't find any mention of a suitable method that treats the data as simply an update, although you could add one. Mapped arrays come with some helpful methods such as mappedIndexOf to help you find particular items. If you receive an update data set simply loop through it, find the item and update it with a mapping.fromJS call to that particular item. This can easily be generalized into reusable method.
You can use ko.mapping.updateFromJS() to update existing values. However, it does not add new values so that would be a problem in your instance. Take a look at the link below for more details.
Using updateFromJS is replacing values when it should be adding them
Yes, you should first collect all data into a list or array and then apply the mapping to that list. Otherwise you are going to overwrite the values in your viewModel.

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