I'm working on an app, which is supposed to show data from two nodes(Firebase). Firebase DB is structured as:
{
"College": {
"4F2EAB65": {
"id": "4F2EAB65",
"name": "SomeCollege"
},
"A3C2ED31": {
"id": "A3C2ED31",
"name": "OtherCollege"
},
"F967B5A0": {
"id": "F967B5A0",
"name": "CoolCollege"
}
},
"Student": {
"3E20545B": {
"college-ID": "4F2EAB65",
"id": "3E20545B",
"name": "A"
},
"6FDEE194": {
"college-ID": "F967B5A0",
"id": "6FDEE194",
"name": "B"
}
}
I want to fetch student details having details: "id", "name", "college-ID", "college-Name"(Need to fetch "college-Name" by "college-ID").
I've achieved this using for loop at front end. Is there any way to get this achieved at Firebase server, also can we make something like join (SQL).
Thanks.
There is no support for server-side joins in the Firebase Realtime Database. Client-side joins are quite normal.
The alternative is to duplicate the data upon writing, so that you don't have to read from two locations.
What's best for your application is a matter of personal preference, your comfort level with the code involved vs data duplication, and the use-cases of your app.
Client-side jons are likely not as slow as you may think. See http://stackoverflow.com/questions/35931526/speed-up-fetching-posts-for-my-social-network-app-by-using-query-instead-of-obse/35932786#35932786
Related
I'm relatively new to CouchDB (more specifically Cloudant if it matters) and I'm having a hard time wrapping my head around something.
Assume the following (simplified) document examples:
{ "docType": "school", "_id": "school1", "state": "CA" }
{ "docType": "teacher", "_id": "teacher1", "age": "40", "school": "school1" }
I want to find all the teachers aged $age (eg. 40) in state $state (eg. CA).
Views only consider one document at a time; that is queries can't directly combine data from different documents. You can query across multiple fields in the same document using Cloudant Query. You can write a selector directly in the Cloudant dashboard. Something like
"selector": {
"age": {
"$gte": 40
},
"state": {
"$eq": "CA"
}
}
See https://cloud.ibm.com/docs/services/Cloudant/tutorials?topic=cloudant-creating-an-ibm-cloudant-query
with the full reference here: https://cloud.ibm.com/docs/services/Cloudant/tutorials?topic=cloudant-query
You could also use a so-called linked document to emulate basic joins, as outlined in the CouchDB docs https://docs.couchdb.org/en/stable/ddocs/views/joins.html
I have incoming Avro records that roughly follow the format below. I am able to read them and convert them in existing NiFi flows. However, a recent change requires me to read from these files and parse the nested record, employers in this example. I read the Apache NiFi blog post, Record-Oriented Data with NiFi
but was unable to figure out how to get the AvroRecordReader to parse nested records.
{
"name": "recordFormatName",
"namespace": "nifi.examples",
"type": "record",
"fields": [
{ "name": "id", "type": "int" },
{ "name": "firstName", "type": "string" },
{ "name": "lastName", "type": "string" },
{ "name": "email", "type": "string" },
{ "name": "gender", "type": "string" },
{ "name": "employers",
"type": "record",
"fields": [
{"name": "company", "type": "string"},
{"name": "guid", "type": "string"},
{"name": "streetaddress", "type": "string"},
{"name": "city", "type": "string"}
]}
]
}
What I hope to achieve is a flow to read the employers records for each recordFormatName record and use the PutDatabaseRecord processor to keep track of the employers values seen. The current plan is to insert the records to a MySQL database. As suggested in an answer below, I plan on using PartitionRecord to sort the records based on a value in the employers subrecord. I do not need the top level details for this particular flow.
I have tried to parse with the AvroRecordReader but cannot figure out how to specify the nested records. Is this something that can be accomplished with the AvroRecordReader alone or does preprocessing, say a JOLT Transform need to happen first?
EDIT: Added further details about database after receiving a response.
What is your target DB and what does your target table look like? PutDatabaseRecord may not be able to handle nested records unless your DB, driver, and target table support them.
Alternatively you may need to use UpdateRecord to flatten the "employers" object into fields at the top level of the record. This is a manual process (until NIFI-4398 is implemented), but you only have 4 fields. After flattening the records, you could use PartitionRecord to get all records with a specific value for, say, employers.company. The outgoing flow files from PartitionRecord would technically constitute the distinct values for the partition field(s). I'm not sure what you're doing with the distinct values, but if you can elaborate I'd be happy to help.
I'm creating an Events app which needs to pull data from a JSON web service to get information about the artists and the shows that are being played. The data will be used to display the line up of artists (a to z) on one view, artists by date and time on another view, and artists by location and sorted by date/time on a third view. We will also allow the user to add shows to their schedule.
The JSON data is similar to this:
Artists feed:
[
{
"artists": {
"3": {
"id": "3",
"title": "Kendrick Lamar",
"subtitle": null,
"imageURL":
"//goevent-images.s3.amazonaws.com/.../web/artist_3_20140331112744_d57b5a70.jpg",
"gcInfo": "artist$kendrick-lamar/3",
"shows": [ {
"id": 153,
"venueTitle": "Sapporo scene",
"formattedDate": "Sunday, August 31",
"date": "2014-08-31",
"title": "Kendrick Lamar"
}
],
"tags": ",8,159,164,",
"color": "#00a0a0",
"dates": [
"2014-08-31"
]
},... },
]
Shows feed:
[
{
"items": {
"197": {
"id": 197,
"title": "Arcade Fire",
"type": "artist",
"dateStart": "2014-08-30",
"timeStart": "16:00:00",
"formattedTimeStart": " 4:00 PM",
"gcInfo": "artist$arcade-fire/127",
"venueId": "1",
"tags": ",80,",
"color": "#337FC3"
}
}
]
Shows and artists will have a many to many relationship. I'll also need to create an entity/table for storing the user's shows that will be added to their personal schedule.
Bands/shows do have the possibility of being removed from the feed, so I think I'll likely need to clear out the artists and shows entities/tables before importing. I'm worried this will break the relationship to the user's scheduled shows.
I also need to download as much of the high-level data as possible upfront so that the app can be used offline as well.
So my question is:
What's the best approach to importing and storing the data for this?
“Best” is subjective. As I understand it, Core Data uses SQLite under the covers, so it's really more a matter of what you're comfortable with.
Have you used Core Data before? If so, use that.
Have you used an SQL Database before? if so, use SQLite.
If you're starting from square one, I supposed I'd recommend Core Data.
Here are a few links to get you started:
Data Management in iOS by Apple
Core Data Programming Guide from Apple.
Core Data Tutorial for iOS: Getting Started
How to Use SQLite to Manage Data in iOS Apps
SQLite Tutorial for iOS: Creating and Scripting
I have three type of documents:
Question
User - contains a source field
Answer - contains the corresponding question ID and user ID
Each questions is answered by multiple users and each user answers each question only once. I want to find for every question how many answers are there answered by users of source "source1".
I think that the nearer that you can arrive to what you want is the following (using Linked documents).
Suppose you have
{ "_id": "user1", "source": "source1" },
{ "_id": "user2", "source": "source2" },
{ "_id": "answer1", "question": "question1", "user": "user1" },
{ "_id": "answer2", "question": "question1", "user": "user2" }
and you define the following view
function(doc) {
if (doc.question) {
emit(doc.question, {_id: doc.user});
}
}
Then if you query that view with key="question1" and with include_docs=true
it will show you all the answers to question1 with all the user information, and you will only have to select those with source = "source1".
For example, with the previous values it will return:
{"total_rows":2,"offset":0,"rows":[
{"id":"answer1","key":"question1","value":{"_id":"user1"},"doc":{"_id":"user1","_rev":"1-c99dc8987841c25c72081a84252793a0","source":"source1"}},
{"id":"answer2","key":"question1","value":{"_id":"user2"},"doc":{"_id":"user2","_rev":"1-0d44e9f4d3806fb932b1b4fcb1e1507b","source":"source2"}}
]}
But AFAIK, what you cannot do in the map function of a view is to use information from other documents.
you can't achieve this within couchdb and need to use thirt-party modules.
for example that one:
sites.google.com/site/nosqldatajoiner/
or google nosql datajoiner
I am working with RavenDB documents. I need to change a field in all the documents at once. I read there is something called set based updates in Raven DB documentation. I need a little help to put me in right direction here.
A patron Document looks something like this:
{
"Privilege": [
{
"Level": "Gold",
"Code": "12312",
"EndDate": "12/12/2012"
}
],
"Phones": [
{
"Cell": "123123",
"Home": "9783041284",
"Office": "1234123412"
}
]
{
In Patrons document collection, there is a Privilege.Level field in each doc. I need to write a query to update it to "Gold" for all documents in that Patrons collection. This is what I know so far. I need to create an Index (ChangePrivilegeIndex) first:
from Patrons in docs.patrons
select new {Patrons.Privilege.Level}
and then write a curl statement to patch documents all at once something like this:
PATCH http://localhost:8080/bulk_docs/ChangePrivilegeIndex
[
{ "Type": "Set", "Name": "Privilege.Level", "Value": "Gold"}
]
I need help to get this to work .. thank you. I know there are lots of loose ends in the actual scripts.. that's why its not working. Can some one look at the scenario and the script above to put me in right direction.