I was wondering whether its possible to pass values to a map function in couchDB design document.
For Example:
In the code below is it possible to pass a value that has been entered by the user and use that value to run the map function. Maybe I can pass users UserName when they login and then display the view based on the map function.
function(doc) {
if(doc.name == data-Entered-By-User) {
emit(doc.type, doc);
}
}
Thank you in advance.
Regards
This is a common mistake in CouchDB when using views. It's kinda confusing, but instead of this:
function (doc) {
if (doc.value === 'thing I am looking for') {
emit(doc.value);
}
}
What you want is this:
function (doc) {
emit(doc.value);
}
And then when you query, you do:
/mydb/_design/myddoc/_view/myview?key="thing I am looking for"
You might want to read my 12 pro tips for better code with PouchDB, especially tip #9. The tips apply equally well to CouchDB. :)
Related
{
"foo":{
"uid":{ // user's uid
"push_key_1":{
"bar":"baz"
},
"push_key_2":{
"bar":"baz"
}
}
}
}
Given the code model above, how do I dynamically search for the push_key_1 or push_key_2 in a query?
I've tried to do :
var searKey = 'push_key_1';
db.ref('foo').orderByKey().equalTo(searKey).once('value')
.then(function(snap){
// snap.val() returns null.
}).catch();
But the snap.val() is null. Turns out orderByKey() is for sorting purposes only. Is there a way to achieve this?
It's a lot simpler than what you're trying. When you know the key of the node you want to load, you don't need a query at all:
db.ref('foo').child(searKey).once('value'....
I think it's not possible unless you restructure the database. My approach is to add another node to store the push keys.
"users_push_keys": {
"push_key_1": "uid_1",
"push_key_2": "uid_1"
}
With this, you can get the uid by retrieving the data from this node.
Hope this helps :)
I have an application where users can follow other users. I want to have a real-time update system, display the total count of followers a user has.
I've just started playing around with Firebase and Pusher, but I don't understand one thing - will each user have their own 'channel'? How would I handle such thing as a follower counter update?
I followed the tutorial and saw that push method can create lists, so one solution I can see is having a list of all the users, each user being an object something like this:
{ username: 'john_doe', follower_count: 6 }
But I don't understand how would I actually track it on the front end? Should I have a filter, something like this?
var user = users.filter(function(user) { return user.username === 'john_doe'; });
// code to display user.follower_count
Or is there a different way that I'm missing?
Most of Firebase logic is based on listeners, you can add a listener to events happening in your collections and when those events happen, you do something.
One way to go about this would be:
var myFollowerListRef = new Firebase(PATH_TO_YOUR_COLLECTION);
myFollowerListRef.on("value", function(snapshot) {
console.log(snapshot.length);
});
This way, every time your follower collection changes, the asynchronous function fires and you can do what you want with the fresh data.
For more information:
https://www.firebase.com/docs/web/guide/retrieving-data.html
Hope this helps, I'm still a beginner in Firebase.
#Th0rndike's approach is the simplest and works fine for relatively short lists. For longer lists, consider using a transaction. From the Firebase documentation on saving transactional data:
var upvotesRef = new Firebase('https://docs-examples.firebaseio.com/android/saving-data/fireblog/posts/-JRHTHaIs-jNPLXOQivY/upvotes');
upvotesRef.transaction(function (current_value) {
return (current_value || 0) + 1;
});
But I recommend that you read the entire Firebase guide. It contains solutions for a lot of common use-cases.
In an effort to prevent certain objects from being created, I set a conditional in that type of object's beforeSave cloud function.
However, when two objects are created simultaneously, the conditional does not work accordingly.
Here is my code:
Parse.Cloud.beforeSave("Entry", function(request, response) {
var theContest = request.object.get("contest");
theContest.fetch().then(function(contest){
if (contest.get("isFilled") == true) {
response.error('This contest is full.');
} else {
response.success();
});
});
Basically, I don't want an Entry object to be created if a Contest is full. However, if there is 1 spot in the Contest remaining and two entries are saved simultaneously, they both get added.
I know it is an edge-case, but a legitimate concern.
Parse is using Mongodb which is a NoSQL database designed to be very scalable and therefore provides limited synchronisation features. What you really need here is mutual exclusion which is unfortunately not supported on a Boolean field. However Parse provides atomicity for counters and array fields which you can use to enforce some control.
See http://blog.parse.com/announcements/new-atomic-operations-for-arrays/
and https://parse.com/docs/js/guide#objects-updating-objects
Solved this by using increment and then doing the check in the save callback (instead of fetching the object and checking a Boolean on it).
Looks something like this:
Parse.Cloud.beforeSave("Entry", function(request, response) {
var theContest = request.object.get("contest");
theContest.increment("entries");
theContest.save().then(function(contest) {
if (contest.get("entries") > contest.get("maxEntries")) {
response.error('The contest is full.');
} else {
response.success();
}
});
}
I've been trying to do Meteor's leaderboard example, and I'm stuck at the second exercise, resetting the scores. So far, the furthest I've got is this:
// On server startup, create some players if the database is empty.
if (Meteor.isServer) {
Meteor.startup(function () {
if (Players.find().count() === 0) {
var names = ["Ada Lovelace",
"Grace Hopper",
"Marie Curie",
"Carl Friedrich Gauss",
"Nikola Tesla",
"Claude Shannon"];
for (var i = 0; i < names.length; i++)
Players.insert({name: names[i]}, {score: Math.floor(Random.fraction()*10)*5});
}
});
Meteor.methods({
whymanwhy: function(){
Players.update({},{score: Math.floor(Random.fraction()*10)*5});
},
}
)};
And then to use the whymanwhy method I have a section like this in if(Meteor.isClient)
Template.leaderboard.events({
'click input#resetscore': function(){Meteor.call("whymanwhy"); }
});
The problem with this is that {} is supposed to select all the documents in MongoDB collection, but instead it creates a new blank scientist with a random score. Why? {} is supposed to select everything. I tried "_id" : { $exists : true }, but it's a kludge, I think. Plus it behaved the same as {}.
Is there a more elegant way to do this? The meteor webpage says:
Make a button that resets everyone's score to a random number. (There
is already code to do this in the server startup code. Can you factor
some of this code out and have it run on both the client and the
server?)
Well, to run this on the client first, instead of using a method to the server and having the results pushed back to the client, I would need to explicitly specify the _ids of each document in the collection, otherwise I will run into the "Error: Not permitted. Untrusted code may only update documents by ID. [403]". But how can I get that? Or should I just make it easy and use collection.allow()? Or is that the only way?
I think you are missing two things:
you need to pass the option, {multi: true}, to update or it will only ever change one record.
if you only want to change some fields of a document you need to use $set. Otherwise update assumes you are providing the complete new document you want and replaces the original.
So I think the correct function is:
Players.update({},{$set: {score: Math.floor(Random.fraction()*10)*5}}, {multi:true});
The documentation on this is pretty thorough.
I am trying to create a webapp on a node/couchdb/windows stack but get terribly stung by what seems to be a lack of experience.
In the database, there is a view that returns all users with passwords. Based on the tutorial for a blog I have tried to access the view through my node code.
Whenever I investigate the structure of the users or users variable, I get an undefined object.
The call to getDatabase() has been tested elsewhere and works at least for creating new documents.
function GetUser(login)
{
var users = GetUsers();
return users[login];
}
function GetUsers() {
var db = getDatabase();
var usersByEmail = [];
db.view("accounts", "password_by_email")
.then(function (resp) {
resp.rows.forEach(function (x) { usersByEmail[x.key] = x.value});
});
//usersByEmail['test'] = 'test';
return usersByEmail;
}
I am aware that both the use of non-hashed passwords as well as reading all users from the database is prohibitive in the final product - just in case anyone wanted to comment on that.
In case something is wrong with the way I access the view: I am using a design document called '_design/accounts' with the view name 'password_by_email'.
Your call to db.view is asynchronous, so when you hit return usersByEmail the object hasn't yet been populated. You simply can't return values from async code; you need to have it make a callback that will execute the code that relies on the result.