I'm trying to avoid adding duplicate objects to an Angular2 array. For example let's say we have an array "Cars" and we put in a JSON object in that array that might be something like:
{
"brand": "Acura"
"engine": "2.4L"
+ others details
}
We can keep adding cars with to the array. My issue is now how to avoid adding the same car into the array again. If I were to add the same JSON as described above, it shouldn't be added. Would I have to iterate through all the existing objects in the array and compare each field of the JSON? This sounds like an expensive operation to me, or is there some more elegant/faster method?
Thanks!
If each car has something unique about it (like an ID), you could use an object instead of an array:
var map = { };
function add(car) {
if (map[car.id]) {
return;
}
map[car.id] = car;
}
Your ID could be something else unique, like a combination of the brand and year or something similar.
map[car.brand + car.year] = car
You need to find or create a unique property on the items in the list, then you could use something like lodash to query the array by a property to see if that item already exists in the list before you add it.
Example from Lodash site
var users = [
{ 'user': 'barney', 'active': false },
{ 'user': 'fred', 'active': false },
{ 'user': 'pebbles', 'active': true }
];
// The `_.matches` iteratee shorthand.
_.findIndex(users, { 'user': 'fred', 'active': false });
Related
I am doing a small project in Angular8 and i have an array which contains data of users as object. This array is provided to me by the client which i can not change.
[
{
id:045#71,
name:'Ahmad',
isActive: false
},
{
id:047#71,
name:'John',
isActive: false
},
{
id:048#71,
name:'Doe',
isActive: false
}
]
In this array i have id's as custom indexes because of which i am not able to iterate this array. I am getting undefined in console when i try to iterate the array . Is there a way to iterate array with custom indexes. I even tried forEach loop but it is not working as well.
The method i used:
usersArray = [
{
id:045#71,
name:'Ahmad',
isActive: false
},
{
id:047#71,
name:'John',
isActive: false
},
{
id:048#71,
name:'Doe',
isActive: false
}
];
ngOnInit() {
this.usersArray.forEach((user)=>{
console.log(user.id + ' - ' + user.name);
})
}
What you have is what we typically call a collection. You can access an item from the collection if you know its index. In most cases, the index is an integer greater or equal to zero. i.e. collection[0] will give you the first item.
You can use collection.find(el => el.id ==='045#71') to find an element in the collection, if it doesn't exist will return undefined.
To find the index of an item you can use collection.findIndex(el => el.id ==='045#71'), in this case it will return 0
If you want to use customer indexes you would have to convert the collection into an object that uses your custom indexes as keys. There's surprisingly also a way to use custom keys in an array but it's not common practice in JavaScript.
How to get a specific dictionary from array of dictionary by giving key alone in method.
we studied about indexOf method in array but we are not sure about how to pass key and get a index of particular key.
Here is Array of dictionary
[
{
"Twitter0":"NSLayoutConstraint"
},
{
"Twitter1":"NSLayoutConstraint"
},
{
"Insta2":"NSLayoutConstraint"
},
{
"Twitter3":"NSLayoutConstraint"
},
{
"Insta4":"NSLayoutConstraint"
}
]
I just want to pass key name like Twitter2 in method.
We tried this Link, we dont know how to process with key
Thanks in advance..
You can use firstIndex(where:) and pass a closure to it:
arrayOfDicts.firstIndex(where: { $0.keys.contains("Twitter2")})
Or more generally with key:
arrayOfDicts.firstIndex(where: { $0.keys.contains(key)})
I have a collection Playlist that contains an array of items
{
userId: {
type : String,
required : true,
index : true,
unique : true
},
items: [
{
id: { // do not mix up with _id, which is the autogenerated id of the pair {id,type}. ID is itemId
type : Schema.Types.ObjectId
},
type: {
type : String
}
}
]
}
Mongo automatically adds the _id field to the items when I push a pair {id,type} to items (but I don't care about it).
Now I would like to remove several "pairs" at once from the items array.
I have tried using $pullAll but it requires an exact match, and I do not know the _id, so it does not remove anything from items
playlistModel.update({userId:userId},{$pullAll:{items:[{id:"123",type:"video"},{id:"456",type:"video"}]}},null,function(err){
I have tried using $pull with different variants, but it removed ALL objects from items
playlistModel.update({userId:userId},{$pull:{items:{"items.id":{$in:["123","456"]}}}},null,function(err){
playlistModel.update({userId:userId},{$pull:{items:{$in:[{id:"123",type:"video"},{id:"456",type:"video"}]}}},null,function(err){
Am I missing something or am I asking something that isn't implemented?
If the latter, is there a way I can go around that _id issue?
OK I found a way that works using $pull:
playlistModel.update({userId:userId},{$pull:{items:{id:{$in:["123","456"]}}}},null,function(err){
It doesn't take the type into account but I can't see any issue with that since the id is unique across all types anyway.
Although I will wait a bit to see if someone has a better solution to offer
EDIT
With Veeram's help I got to this other solution, which IMO is more elegant because I don't have _ids that I don't need in the database, and the $pullAll option seems more correct here
var playlistItemSchema = mongoose.Schema({
id: { // do not mix up with autogenerated _id. id is itemId
type : Schema.Types.ObjectId
},
type: {
type : String
}
},{ _id : false });
var schema = new Schema({
userId: {
type : String,
required : true,
index : true,
unique : true
},
items: [playlistItemSchema]
});
playlistModel.update({userId:userId},{$pullAll:{items:[{id:"123",type:"video"},{id:"456",type:"video"}]}},null,function(err){
tips:
you can use _id field to handle your playlistModel data.
mongoose api : new mongoose.Types.ObjectId to generate an Object_id
let _id=new mongoose.Types.ObjectId;
playlistModel.updateMany({_id:_id},{ $set: { name: 'bob' }}).exec(data=>{console.log('exec OK')});
I'm working with a weird data model (no way around it at this point). I'm using restangular to make a rest call to get back a single resource object
Normally, the resource object returned by restangular is just whatever I set my
$scope.resource = response to and I can do resource.name , resource.id in the view/template, etc..
Except this group of resources instead of returning the key, value pairs in the response object, it returns an object within an object like so
resource1: {name: 'value', stuff: 'value', etc}
which is fine because then I would just set my $scope.resource = response.resource1 in my controller
except the problem is, is that there's 5 different kind of resource object names so if I make a resource by id call I might get back resource2, resource4, resource1, etc. so setting my $scope.resource = response.resource1 would only work when I get resource1.
My first attempt to solve this was to just use ng-repeat in which I set
<ul ng-repeat="(resource, value) in resource">
<li class="list-group-item">
Name:
<span class="pull-right"> {{ resource.name }} </span>
</li>
</ul>
which works great except because restangular returns all this extra stuff it's looping through each object it's repeating a bunch of blank html stuff if that makes sense.
My other thought was to try making a constant and make an object that has all 5 resources there and my ng-repeat would only populate based off that constant object (ie: it would check for those strings "resource1, resource2, etc" and if it's there then it will populate the template. But I'm not exactly sure how to do this.
Any other options or are there ng-repeat features i'm just not utilizing? any Help thanks
Here's the example I will be working from. Initially your incoming data looks something like this I believe...
$scope.data = [
{
resource1 : { name: 'r1' }
},
{
resource2 : { name: 'r2' }
},
{
resource2 : { name: 'r2' }
}];
When you receive the data you can normalize it by flattening it out into the following structure...
$scope.normalized = [
{ name : 'r1' },
{ name : 'r2' },
{ name : 'r2' }
];
Or you can add a common field for the object "type"
$scope.expanded = [
{
type : 'resource1',
resource1 : { name: 'r1' }
},
{
type : 'resource2',
resource2 : { name: 'r2' }
},
{
type : 'resource2',
resource2 : { name: 'r2' }
}];
Or you can normalize but retain type data...
$scope.normalizedType = [
{ type : 'resource1', name : 'r1' },
{ type : 'resource2', name : 'r2' },
{ type : 'resource2', name : 'r2' }
];
Normalizing upon retrieval of the data is probably your best bet. The question then becomes do you need to retain the objects type information.
So another solution I came up with was put all the resource key names into a list
resources = ['resource1', 'resource2', 'resource3', 'etc..']
and in my restangular service promise I just checked for which resource number it would be with a for loop like this
return ResourceRestangular.all('resource').get(resourceId).then(function(response){
for (i = 0; i < resources.length ; i++){
if (resources[i] in response){
self.resource = response[resources[i]];
}
}
return self.resource;
No need for ng-repeat anymore!
Currently trailing out Mongoose and MongoDB for a project of mine but come across a segment where the API is not clear.
I have a Model which contains several keys and documents, and one of those keys os called watchList. This is an array of ID's that the user is watching, But I need to be sure that these values stay unique.
Here is some sample code:
var MyObject = new Mongoose.Schema({
//....
watching : {type: Array, required: false},
//....
});
So my question is how can I make sure that the values pushed into the array only ever store one, so making the values unique, can i just use unique: true ?
Thanks
To my knowledge, the only way to do this in mongoose is to call the underlying Mongo operator (mentioned by danmactough). In mongoose, that'd look like:
var idToUpdate, theIdToAdd; /* set elsewhere */
Model.update({ _id: idToUpdate },
{ $addToSet: { theModelsArray: theIdToAdd } },
function(err) { /*...*/ }
);
Note: this functionality requires mongoose version >= 2.2.2
Take a look at the Mongo documentation on the $addToSet operator.
Mongoose is an object model for mongodb, so one option is to treat the document as a normal javascript object.
MyModel.exec(function (err, model) {
if(model.watching.indexOf(watchId) !== -1) model.watching.push(watchId);
model.save(...callback);
});
Although, I do agree that mongoose should have some support for this built in the form of a validator for the collection document reference feature-- especially because most of the time you want to add only unique references.
That's how you can do it using Mongoose,
IF your upcoming value is an Array
Model
.findOneAndUpdate({ _id: yourID },
{ $addToSet: { watching: { $each: yourWatchingArr } } },
function(err) { /*...*/ }
);
IF your upcoming value is a string
Model
.findOneAndUpdate({ _id: yourID },
{ $addToSet: { watching: yourStringValue } },
function(err) { /*...*/ }
);