javascript - Firebase retrieve data by key -


i have firebase node follows -

providers   -userid1    --userid : userid1    --keywords      ---key1 : true      ---key2 : true      ---key3 : true   -userid2    --userid : userid2    --keywords      ---key1 : true      ---key4 : true      ---key5 : true

i want retrieve userids have "key1" in keywords child.

i tried following query

var ref = new firebase(url+"/providers") ref.orderbychild("keywords").equalto("key1").on("value", function(snapshot){ console.log(snapshot.numchildren()); })

also tried -

var ref = new firebase(url+"/providers") ref.orderbykey().equalto("key1").on("value", function(snapshot){ console.log(snapshot.numchildren()); })

i no results. missing in query? how above 2 queries different? both queries don't work.

your key1 key, while equalto() used check values.

the trick query records key1 key has value of true: 

var ref = new firebase(url+"/providers") ref.orderbychild("keywords/key1").equalto(true).on("value", function(snapshot){     console.log(snapshot.numchildren()); })

don't forget add indexes on keywords/key1, etc. rules.json:

"providers": {   "$uid": {     ".indexon": ["keywords/key1", "keywords/key2", "keywords/key3", "keywords/key4", "keywords/key5"]   } }

you'll find adding such indexes unmaintainable, indication data structure should improved. in case, can done adding secondary, inverted index maps each specific key matching providers:

providers   userid1     userid : userid1     keywords       key1 : true       key2 : true       key3 : true   userid2     userid : userid2     keywords       key1 : true       key4 : true       key5 : true providers_by_keyword:   key1:     userid1: true     userid2: true   key2:     userid1: true   key3:     userid1: true   key4:     userid2: true   key5:     userid2: true

now can execute both operations without query:

  1. get keywords user1: ref.child('users/user1/keywords').on(...
  2. get users key1: ref.parent().child('providers_by_keyword/key1').on(...

this approach of creating secondary indexes known denormalizing in nosql databases. described in firebase's denormalizing normal blog post. recommend reading article nosql data modeling.


Comments

Post a Comment

Popular posts from this blog

get url and add instance to a model with prefilled foreign key :django admin -

Image
i have page in each contest shown in row. each row contains contest id , link other model names have foreign key contest. news model: class news(models.model): title = models.charfield(max_length=50, null=true) description = models.textfield() time = models.timefield( default= datetime.datetime.now().time()) contest = models.foreignkey(contest) i want use admin adding , changing these models. want when user clicks on 'news' has foreign key contest id=1, shows list of news value foreign key. use {% instance in instances %} <tr class="{% cycle 'row1' 'row2' %}"> <td>{{ instance.title }}</td> <td>{{ instance.starttime }}</td> <td>{{ instance.timespan }}</td> <td>{{ instance.date }}</td> <td><a href="/adm...
Read more

css - Make div keyboard-scrollable in jQuery Mobile? -

from can tell, although jquery-mobile-powered pages can contain divs overflow set scroll or auto, , these divs can scrolled one-screen bar or mouse wheel, cannot scrolled using arrow keys, page-up/page-down, or home/end. instead, official "page" div (with data-role="page") absorbs input. perhaps other divs can't acquire focus, i'm not sure. is there way around this? edit: jsfiddle of simple example: https://jsfiddle.net/qogz0shx/ <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script> <script src="https://ajax.googleapis.com/ajax/libs/jquerymobile/1.4.5/jquery.mobile.min.js"> </script> <link rel="stylesheet" href="https://code.jquery.com/mobile/1.4.5/jquery.mobile-1.4.5.css"/> <style> #outer { overflow:scroll; height: 50vh; width: 50vw; } #inner { height: 500vh; width: 500vw; } ...
Read more

ruby on rails - Seeing duplicate requests handled with Unicorn -

recently upgraded our ec2 instances c3.large in order boost more unicorn workers handle increased traffic our site. (6xworkers per machine - 2 ec2 instances). when did this, started seeing duplicate records being created! looks somehow, maybe 2 unicorn workers attempting process same request? in nginx logs see 1 [post] request particular rails controller - yet 2 records being created in database. i'm hitting kind of race condition issue - have no idea how debug this. doesn't happen time, when it's frustrating well. noticed 2 database records within 5 seconds of each other. (and yes disable button when user clicks submit button). unicorn 4.8.2 ruby 1.9.3 rails 3.2.14 any great! thanks! although may not fix problem, upgrade ruby 2.0.0. there blog mentioning idea upgrade ruby 2.0.0 if using unicorn. for example: https://www.digitalocean.com/community/articles/how-to-optimize-unicorn-workers-in-a-ruby-on-rails-app specifically: if using ruby 1.9, ...
Read more