update a Array without duplicate Map based on a parameter - javascript

I am currently using ArrayUnion to update an Array in a Document in Firebase. It Consists of a Map of the format {userid:XXXXXX,value:01234}. Now lets say I want to change this value, I was initially thinking of just using ArrayUnion and send an updated map, But how do I remove the pre-existing Map. (In Other Words No Too Map in the array can have the same ID).
Seems like a long shot, but I was also thinking maybe we can just use a Map which has a timestamp attribute to showing when it was added, and then on the client side ill perform the actions of removing those entries which are older.
Which of the options is better? and do you have any better solutions for the same problem?
(Note: Using Firebase v9 for Web)

The only way you can remove a map item from an array without reading the document first is if you know the entire contents of the map ahead of time. If you do, you can use arrayRemove, passing the entire map as an argument.
If you don't know the entire map contents, then your only option is to read the document into memory, modify the array the way you want in memory, then write the entire updated array field back to the document.
It is not possible to do anything with a map inside an array if you don't know its entire contents. If you only know one field, you can't update it and you can't use it in a query.
See:
Firestore Update single item in an array field
How to update an "array of objects" with Firestore?

Related

Data masking in MongoDB

We have a MongoDB database in a development environment. There are a lot of collections that contain names of people. What we want to do is the following:
mask the names in each collection, the fields need to be updated directly in the database, cannot run them through some external pipeline
once masked, it is ok if we are unable to retrieve the original names (so one-way masking)
every unique name should result in the same mask
the masking script can be run on the mongodb cli or a MongoDB gui like Studio3T
I was thinking of maybe using MD5 or SHA, but I am not sure if either is available to use directly in mongo operations like update or even in javascript without external libraries.
Also, since MD5 always produces the same hash, if someone were to get access to the document, since we will not be masking the field name, it would be fairly easy to feed typical names into the algorithm until the hash matches to figure out the name, but I think we may be able to live with this.
An alternative I was thinking of was, to loop through the unique names we have, and create a map from names to UUIDs. Then, go through each collection and use this map to update the names with the UUIDs. The problem with this is that we'll need to keep this mapping dictionary for when we receive additional documents for an existing person.

Firebase Firestore - Query for posts in a big collection where groupId should match a value in an array

I am having troubles with firebase using the cloudstore .where query.
I want to query a big collection of documents (in my case posts) but I only want to query the posts in which the groupId matches any of the groups that the user is in. The reason for this is that I want to query a combined feed for the user with all the latest relevant data (using orderBy and limit).
I know that I can use array-contains, so I could for instance query all of the posts for user where the user is a member.
firebase.db.collection('posts').where('members','array-contains',firebase.uid)
This would work if I decided to keep track of the members in a group. Problem is if I would change members in a group, I would have to loop through all posts and change the array of members (not really good practice). Better would then be to have the post contain and id of which group it was posted in.
So let's say the user has an array containing all the groups he is in
user.groups = ['companyGroup', '{id}', '{id2}']
I would then like to query through the whole posts collection and get all the documents where the field groupId matches any of the values in user.groups something like this:
firebase.db.collection('posts').where('groupId','==',[any of user.groups])
or maybe the reverse:
firebase.db.collection('posts').where(user.groups,'array-contains','groupId')
^ I have not tried this one but I am certain it doesn't work according to the docs according to
The where() method takes three parameters: a field to filter on, a comparison operation, and a value. The comparison can be <, <=, ==, >, >=, or array_contains.
Is there a possible way to do something like this? I can't really query multiple locations at once and combine them because that defeats the purpose of being able to limit the data and orderBy fields. I understand that I could put a new collection called feed under every user and for every post use a firebase function that pushes to post to the relevant members feed (only the id and latestActivity), but then as soon as that post changes (I am going to use a field called latestActivity to order data according to relevancy, but also when deleting a post) I would need to loop through all docs under every user affected and change the value/delete doc.
Any ideas are greatly appreciated!
Currently, there is no way to pass an array of ids to the where() function and expect to get all the documents that corresponde to each particular id:
firebase.db.collection('posts').where('groupId','==',[any of user.groups])
The option that you have, is to store in the array either the ids as strings or references (path to group documents). There is no real advantage of storing references rather than strings, so it's up to you to decide which one you feel more comfortable with.
To get the all group documents, you should get the array that contains those ids/references and for each one separately create a new database request. So unfortunately there is no other way to get those group documents at once using a single query.
However, creating extra database calls it doesn't mean that fetching, let's say 3 documents, will be 3x slower as fetching one document. You can make some tests yourself.
I quote #Frank van Puffelen, "Firebase has a history of performing fine in such cases, since it pipelines the requests."
use array contain it works perfectly.
firebase.db.collection('posts').where(user.groups,'array-contains','groupId')
it works pretty good for me . you should try this.

How to receive following data structure in Firebase from website using JavaScript and PHP?

I want to receive data from JavaScript file using PHP in Firebase in following structure.
Not like this.
From how I understood your question, I think you're looking to have your data to be added with an auto-generated Firebase id. So I think what you're looking for is the push() method:
Generates a new child location using a unique key and returns its Reference.
This is the most common pattern for adding data to a collection of items.
If you provide a value to push(), the value will be written to the generated location. If you don't pass a value, nothing will be written to the Database and the child will remain empty (but you can use the Reference elsewhere).
The unique key generated by push() are ordered by the current time, so the resulting list of items will be chronologically sorted. The keys are also designed to be unguessable (they contain 72 random bits of entropy).
Also see Firebase Database: Read and Write Data on the Web - Update specific fields.

Can multiple "d3.js Dendrogram" nodes point to the same leaf node?

I've started a new JavaScript project based on the example at:
http://bl.ocks.org/mbostock/4063570
Everything with the d3 Dendrogram is great so far except that my data will probably always contain duplicate leaves (terminal nodes). In my data only the leaves could ever contain duplicate data. All internal nodes (between root and leaves) are strictly distinct well before d3 comes into play.
I could add something to the node(s) name (d.name) to make each node totally unique, but I'd rather 'reuse' leaf nodes and make all internal nodes point to and share a single leaf if possible.
Does anyone out there know how to do this?
Many thanks in advance!
Drew Barfield
The D3 data join expects that each DOM node will correspond to a different element in the data array. However, there's nothing stopping 2 elements in the data array from referring to the same underlying object.
It comes down to whether you are OK with the default join key (which is array index) or if you want to achieve a sense of "object permanence" on data update by mapping specific data elements to specific nodes. To have that happen you need to define a custom join key function, which by definition relies on some way to differentiate the data elements.
Personally, I think that if you're doing any amount of data updating involving enter/exit/update, life will be much easier if each data element is unique and has some kind of "id" or "key" property that you can use to identify it. Reusing data elements will likely be more headache than it's worth.
You didn't actually mention what you are trying to achieve by sharing data? Is it just a memory saving optimization or is there another reason? If it's just memory, I wouldn't bother.

Can you store a reference to a mongo collection?

At the top of a file can I put something like...
var collection = db.mongo.collection('test', function(err, collection){return collection});
and then in any of the files functions use collection.find() etc
I guess my question is... is collection a reference to the collection or a copy of the data?
If data in the collection changes will i still get up to date data by querying the collection variable?
Thanks!!
Collection is a reference for the collection object. Until you issue a find (or findOne) you don't have real data in your hands. And even then, it returns a Cursor object leaving the collection object always untouched.
Storing both Collections or cursors will not store your data. remember that you could be dealing with millions of records. dealing with data itself could be overwhelming for the server memory. Instead, mongo returns cursors and references for you to filter away. In PHP you have a function called iterator_to_array that you can pass it the cursor and it converts to an array of data. In javascript I don't know if there is such functions. But I guess it doesn't makes sense to be such functions. Filter the information until you have manageable data size, then iterate over the cursor and do your thing. If you have something like a config array or such, intead of several documents, try to store everything on one and fetch it with the findOne() function.
But in the end I guess that's just a design question whether your data is possible to filter or not.

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