KISS Datatable

Recenlty I’ve faced a problem with sorting columns in Datatable.

What is Datatable?

Datatable is a plug-in for Jquery library. It provides a lot of features like pagination, quick search or multi-column ordering. Besides, you can develop easily Bootstrap or Foundation ui css styles. There are also more other option but It doesn’t make sense to list it here, because you can visit their site and you can read clearly documentation. On Datatable website you can see a lot of examples. First of them shows how to improve your ordinary table to awesome and rich of features table. One function changes everything, It’s fantastic!  

$('#myTable').DataTable();

Returning to my problem which I’ve faced, as I told it was problem related to sorting column in table.

I know sorting is a trivial thing. I hope that everyone knows it 🙂 Sorting by a date is also implemented in a datatable library. So everything is clear when we don’t change date format to human readable format. I mean something like this ‘3 hours ago’, ‘1 year ago’.

When Open Event team tested how datatable manages ordering columns in that format it didn’t work. It’s quite hard to sort by that format, So I’ve invented an idea. Surely you are wondering what i’ve invented. I’ve postponed my minds about sort by this values. It can direct to overwork. When I thought about it, weird ideas came to my mind, a lots of conditions, If statements… Therefore I’ve resigned from this. I’ve used KISS principle. KISS means ‘keep it simple stupid’. I like it!

Therefore that sorting is implemented on frontend side. I’ve decided not to display human readable date format at the beginning. I find  all dates which have format “YYYY-MM-DD HH:mm” then I replace that format to human readable format. So it’s very quick and comfortable, and doesn’t require a lot conditions to write. Of course I’ve tried to implement it in Datatable library. I suppose that it would  require more effort than it’s now.

Below You can see great function which changes a date in frontend side but does not change data in a datatable. So sorting process takes place in a datatable using format  “YYYY-MM-DD HH:mm” but user see human readable format. Isn’t it awesome?!

function change_column_time_to_humanize_format(datatable_name, column_id) {
  $(datatable_name).each(function( key, value ) {
    $(value).children().each(function( key1, value2 ) {
       if(key1 === column_id ){
          var current_value = $(value2).text().slice(0, 16);
          var changed_value = moment(current_value, "YYYY-MM-DD hh:mm").fromNow()
          var isValid = moment(current_value, "YYYY-MM-DD HH:mm", true).isValid()
          if (changed_value !== current_value && isValid === true){
              $(value2).text(changed_value)
          }
      }
  });
});

 

Twitter Section Using loklak webtweets

In Open event web app, the user can provide URL of social links such as Twitter, Facebook etc in the event.json file inside the ZIP. The previous functionality was to use Twitter API and to generate a timeline showing the tweets of the twitter URL mentioned in event.json by user. But, it can be done by following another approach which reduces the third party dependency i.e Loklak-webtweets.

I have implemented the twitter section using loklak webtweets which can be done very easily.

Step 1:  Including necessary files from loklakwebtweets repository inside index.html. You can find them in js/ folder of this repository.

<script src="./dependencies/jquery.min.js"></script>
<script src="./dependencies/bootstrap.min.js" type="text/javascript"></script>
<script src="./dependencies/loklak-fetcher.js" type="text/javascript"></script>
 <script src="./dependencies/tweets.js" type="text/javascript"></script>

 

Step 2:  Specify the data source in HTML from which twitter data will be fetched. Here I have extracted the last word from the twitter URL provided by the user and passed it to HTML.

const sociallinks = Array.from(event.social_links);
 var twitter ="";
 sociallinks.forEach((link) => {
  if(link.name.toLowerCase() === "twitter") {
   twitter = link.link;
  }
 }) 
 const arrayTwitterLink = sociallink.split('/');
 const twitterLink = arrayTwitterLink[arrayTwitterLink.length - 1];
 
 const urls= {
   twitterLink: twitterLink,
   tweetUrl: twitter,
 };

This code will search twitter link in social links array present in event.json and get its last character which will be provided to data-from and data-query attribute of HTML.

 <section class="sponsorscont">
  <div class="tweet-row">
   <div class="col-sm-12 col-md-12 col-xs-12">
    <i class ="social_twitter fa fa-twitter"></i>
     <div class="tweets-feed" id="tweets" data-count=50 data-query="    {{{eventurls.twitterLink}}}" data-from="{{{eventurls.twitterLink}}}">
     <div class="arrow-up"></div>
      <p id="tweet" class="tweet">
       Loading...
     </p>
   <span style="margin-bottom: 20px;" id="dateTweeted"></span>
    <p>Follow<u>
    <b><a href="{{eventurls.tweetUrl}}"/>
     @{{eventurls.twitterLink}}</a>
    </b></u> for more updates</p> 
     </div> 
    </div>
  </div>
</section>

Step 3 : Now we just need to add styling so that it looks decent. For that, I have written some SASS.

.tweets-feed {
   color: $black;
   line-height: 30px;
   font-size: 20px;
   transition: opacity 0.2s linear;
   margin-bottom: 20px;
   height: 100px;
 
  a {
   color: $black;
   text-decoration: underline;
   font-weight: 700;
  } 

  #dateTweeted {
   font-size: 15px;
   display: block;
  }

}

.tweet-row {
   padding: 0 80px;
   margin-bottom: 80px;
   .social_twitter {
     font-size: 60px;
     margin-bottom: 12px;
  }
}

The output from the above code is a well designed Twitter section fetching tweets from the URL provided as a string in event.json by user.

tweet

 

Building the Scheduler UI

{ Repost from my personal blog @ https://blog.codezero.xyz/building-the-scheduler-ui }

If you hadn’t already noticed, Open Event has got a shiny new feature. A graphical and an Interactive scheduler to organize sessions into their respective rooms and timings.

As you can see in the above screenshot, we have a timeline on the left. And a lot of session boxes to it’s right. All the boxes are re-sizable and drag-drop-able. The columns represent the different rooms (a.k.a micro-locations). The sessions can be dropped into their respective rooms. Above the timeline, is a toolbar that controls the date. The timeline can be changed for each date by clicking on the respective date button.

The Clear overlaps button would automatically check the timeline and remove any sessions that are overlapping each other. The Removed sessions will be moved to the unscheduled sessions pane at the left.

The Add new micro-location button can be used to instantly add a new room. A modal dialog would open and the micro-location will be instantly added to the timeline once saved.

The Export as iCal allows the organizer to export all the sessions of that event in the popular iCalendar format which can then be imported into various calendar applications.

The Export as PNG saves the entire timeline as a PNG image file. Which can then be printed by the organizers or circulated via other means if necessary.

Core Dependencies

The scheduler makes use of some javascript libraries for the implementation of most of the core functionality

  • Interact.js – For drag-and-drop and resizing
  • Lodash – For array/object manipulations and object cloning
  • jQuery – For DOM Manipulation
  • Moment.js – For date time parsing and calculation
  • Swagger JS – For communicating with our API that is documented according to the swagger specs.
Retrieving data via the API

The swagger js client is used to obtain the sessions data using the API. The client is asynchronously initialized on page load. The client can be accessed from anywhere using the javascript function initializeSwaggerClient.

The swagger initialization function accepts a callback which is called if the client is initialized. If the client is not initialized, the callback is called after that.

var swaggerConfigUrl = window.location.protocol + "//" + window.location.host + "/api/v2/swagger.json";  
window.swagger_loaded = false;  
function initializeSwaggerClient(callback) {  
    if (!window.swagger_loaded) {
        window.api = new SwaggerClient({
            url: swaggerConfigUrl,
            success: function () {
                window.swagger_loaded = true;
                if (callback) {
                    callback();
                }

            }
        });
    } else {
        if (callback) {
            callback();
        }
    }
}

For getting all the sessions of an event, we can do,

initializeSwaggerClient(function () {  
    api.sessions.get_session_list({event_id: eventId}, function (sessionData) {
        var sessions = sessionData.obj;  // Here we have an array of session objects
    });
});

In a similar fashion, all the micro-locations of an event can also be loaded.

Processing the sessions and micro-locations

Each session object is looped through, it’s start time and end time are parsed into moment objects, duration is calculated, and it’s distance from the top in the timeline is calculated in pixels. The new object with additional information, is stored in an in-memory data store, with the date of the event as key, for use in the timeline.

The time configuration is specified in a separate time object.

var time = {  
    start: {
        hours: 0,
        minutes: 0
    },
    end: {
        hours: 23,
        minutes: 59
    },
    unit: {
        minutes: 15,
        pixels: 48,
        count: 0
    },
    format: "YYYY-MM-DD HH:mm:ss"
};

The smallest unit of measurement is 15 minutes and 48px === 15 minutes in the timeline.

Each day of the event is stored in a separate array in the form of Do MMMM YYYY(eg. 2nd May 2013).

The array of micro-location objects is sorted alphabetically by the room name.

Displaying sessions and micro-locations on the timeline

According to the day selected, the sessions for that day are displayed on the timeline. Based on their time, the distance of the session div from the top of the timeline is calculated in pixels and the session box is positioned absolutely. The height of the session in pixels is calculated from it’s duration and set.

For pixels-minutes conversion, the following are used.

/**
 * Convert minutes to pixels based on the time unit configuration
 * @param {number} minutes The minutes that need to be converted to pixels
 * @returns {number} The pixels
 */
function minutesToPixels(minutes) {  
    minutes = Math.abs(minutes);
    return (minutes / time.unit.minutes) * time.unit.pixels;
}

/**
 * Convert pixels to minutes based on the time unit configuration
 * @param {number} pixels The pixels that need to be converted to minutes
 * @returns {number} The minutes
 */
function pixelsToMinutes(pixels) {  
    pixels = Math.abs(pixels);
    return (pixels / time.unit.pixels) * time.unit.minutes;
}
Adding interactivity to the session elements

Interact.js is used to provide interactive capabilities such as drag-drop and resizing.

To know how to use Interact.js, you can checkout some previous blog posts on the same, Interact.js + drag-drop and Interact.js + resizing.

Updating the session information in database on every change

We have to update the session information in database whenever it is moved or resized. Every time a session is moved or resized, a jQuery event is triggered on $(document) along with the session object as the payload.

We listen to this event, and make an API request with the new session object to update the session information in the database.


The scheduler UI is more complex than said in this blog post. To know more about it, you can checkout the scheduler’s javascript code atapp/static/js/admin/event/scheduler.js.

R14 – Memory Quota Exceeded

We, like many other organisations, are using heroku as the deployment server for our project open event organizer server. Things are pretty simple and awesome when your project is in its beginning phase and things run pretty smoothly. But as your project grows, there comes some server problem. And one of the biggest problems as your project grows is memory. Now since various packages have a different amount of memory assigned to you in case of hosting in generic servers such as heroku, so it might result in memory quota exceeded. Recently, we faced such a problem. R14 – Memory Quota Exceeded. Took us quite some time to understand what and why and how this occurred. So let me share a few things I found about this error.

Continue reading R14 – Memory Quota Exceeded

Python code examples

I’ve met many weird examples of  behaviour in python language while working on Open Event project. Today I’d like to share some examples with you. I think this knowledge is necessary, if you’d like to increase a  bit your knowledge in python area.

Simple adding one element to python list:

def foo(value, x=[]):
  x.append(value)
  return x

>>> print(foo(1))
>>> print(foo(2))
>>> print(foo(3, []))
>>> print(foo(4))

OUTPUT

[1] 
[1, 2] 
[3]
[1, 2, 4]

First output is obvious, but second not exactly. Let me explain it, It happens because x(empty list) argument is only evaluated once, So on every call foo(), we modify that list, appending a value to it. Finally we have [1,2, 4] output. I recommend to avoid mutable params as default.

Another example:

Do you know which type it is?

>>> print(type([ el for el in range(10)]))
>>> print(type({ el for el in range(10)}))
>>> print(type(( el for el in range(10))))

Again first and second type are obvious <class ‘list’>, <class ‘set’>. You may  think that last one should return type tuple but it returns a generator <class ‘generator’>.

Example:

Do you think that below code returns an exception?

list= [1,2,3,4,5]
>>> print(list [8:])

If you think that above expression returns index error you’re wrong. It returns empty list [].

Example funny boolean operators

>>> 'c' == ('c' or 'b')
True
>>> 'd' == ('a' or 'd')
False
>>> 'c' == ('c' and 'b')
False 
>>> 'd' == ('a' and 'd')
True

You can think that that OR and AND operators are broken.

You have to know how python interpreter behaves while looking for OR and AND operators.

So OR Expression takes the first statement and checks if it is true. If the first statement is true, then Python returns object’s value without checking second value. If first statement is false interpreter checks second value and returns that value.

AND operator checks if first statement is false, the whole statement has to be false. So it returns first value, but if first statement is true it checks second statement and returns second value.

Below i will show you how it works

>>> 'c' == ('c' or 'b')
>>> 'c' == 'c'
True
>>> 'd' == ('a' or 'd')
>>> 'd' == 'a'
False
>>> 'c' == ('c' and 'b')
>>> 'c' == 'b'
False 
>>> 'd' == ('a' and 'd')
>>> 'd' == 'd'
True

I hope that i have explained you how the python interpreter checks OR and AND operators. So know above examples should be more understandable.

Resizing Uploaded Image (Python)

While we make websites were we need to upload images such as in event organizing server, the image for the event needs to be shown in various different sizes in different pages. But an image with high resolution might be an overkill for using at a place where we just need it to be shown as a thumbnail. So what most CMS websites do is re-size the image uploaded and store a smaller image as thumbnail. So how do we do that? Let’s find out.

Continue reading Resizing Uploaded Image (Python)

Accepting Stripe payments on behalf of a third-party

{ Repost from my personal blog @ https://blog.codezero.xyz/accepting-stripe-payments-on-behalf-of-a-third-party }

In Open Event, we allow the organizer of each event to link their Stripe account, so that all ticket payments go directly into their account. To make it simpler for the organizer to setup the link, we have a Connect with stripe button on the event creation form.

Clicking on the button, the organizer is greeted with a signup flow similar to Login with Facebook or any other social login. Through this process, we’re able to securely and easily obtain the credentials required to accept payments on behalf of the organizer.

For this very purpose, stripe provides us with an OAuth interface called as Stripe Connect. Stripe Connect allows us to connect and interact with other stripe accounts through an API.

We’ll be using Python’s requests library for making all the HTTP Requests to the API.
You will be needing a stripe account for this.

Registering your platform
The OAuth Flow

The OAuth flow is similar to most platforms.

  • The user is redirected to an authorization page where they login to their stripe account and authorize your app to access their account
  • The user is then redirected back to a callback URL with an Authorization code
  • The server makes a request to the Token API with the Authorization code to retrieve the access_token, refresh_token and other credentials.

Implementing the flow

Redirect the user to the Authorization URL.
https://connect.stripe.com/oauth/authorize?response_type=code&client_id=ca_8x1ebxrl8eOwOSqRTVLUJkWtcfP92YJE&scope=read_write&redirect_uri=http://localhost/stripe/callback  

The authorization url accepts the following parameters.

  1. client_id – The client ID acquired when registering your platform.required.
  2. response_type – Response type. The value is always code. required.
  3. redirect_uri – The URL to redirect the customer to after authorization.
  4. scope – Can be read_write or read_only. The default is read_only. For analytics purposes, read_only is appropriate; To perform charges on behalf of the connected user, We will need to request read_write scope instead.

The user will be taken to stripe authorization page, where the user can login to an existing account or create a new account without breaking the flow. Once the user has authorized the application, he/she is taken back to the Callback URL with the result.

Requesting the access token with the authorization code

The user is redirected back to the callback URL.

If the authorization failed, the callback URL has a query string parameter error with the error name and a parameter error_description with the description of the error.

If the authorization was a success, the callback URL has the authorization code in the code query string parameter.

import requests

data = {  
    'client_secret': 'CLIENT_SECRET',
    'code': 'AUTHORIZATION_CODE',
    'grant_type': 'authorization_code'
}

response = requests.post('https://connect.stripe.com/oauth/token', data=data)

The client_secret is also obtained when registering your platform. The codeparameter is the authorization code.

On making this request, a json response will be returned.

If the request was a success, the following response will be obtained.

{
  "token_type": "bearer",
  "stripe_publishable_key": PUBLISHABLE_KEY,
  "scope": "read_write",
  "livemode": false,
  "stripe_user_id": USER_ID,
  "refresh_token": REFRESH_TOKEN,
  "access_token": ACCESS_TOKEN
}

If the request failed for some reason, an error will be returned.

{
  "error": "invalid_grant",
  "error_description": "Authorization code does not exist: AUTHORIZATION_CODE"
}

The access_token token obtained can be used as the secret key to accept payments like discussed in Integrating Stripe in the Flask web framework.

Twitter Oauth

Oauth_logo.svg.png

What is Oauth?

It’s an open protocol which allows to secure an authorization in a simple and standard method from web, mobile and desktop applications.Facebook, Google Twitter, Github and more web services use this protocol to authenticate user. Using Oauth is very convenient, because it delegates user authentication to the service which host user account. It allows us to get resources from another web service without giving any login or password. If you have a service and want to prepare a authentication via Twitter, the best solution is to use OAuth. Recently Open Event team met a problem in an user profile page. We’d like to automatically fill information about user. Of course, to solve it we use Oauth protocol, to authenticate with Twitter After a three-steps authentication we can get name and profile picture.If you need another information from Twitter profile like recent tweets or followers’ list. You have to visit Twitter API site to see more samples of resource which you can get

How do Open event team implement communication between Orga-server and Twitter?

All services have a very similar flow. Below i will show you how it looks in our case.

Before starting you need to create your own twitter app. You can create app in Twitter apps site https://apps.twitter.com/. If  create an app you will see a CONSUMER KEY and CONSUMER SECRET KEY which shouldn’t be human-readable, so remember not to share these keys.

Below example shows how to get basic information about twitter profile

We use oauth2 python library https://github.com/joestump/python-oauth2

consumer = oauth2.Consumer(key=TwitterOAuth.get_client_id(),

                          secret=TwitterOAuth.get_client_secret())

client = oauth2.Client(consumer)

TwitterOAuth.get_client_id() CONSUMER KEY

TwitterOAuth.get_client_secret()  – CONSUMER SECRET KEY

Then we send GET request to request_token endpoint to get oauth_token

client.request('https://api.twitter.com/oauth/request_token', "GET")
Response: oauth_token=Z6eEdO8MOmk394WozF5oKyuAv855l4Mlqo7hhlSLik&
oauth_token_secret=Kd75W4OQfb2oJTV0vzGzeXftVAwgMnEK9MumzYcM&
oauth_callback_confirmed=true

Next step is to redirect user to Twitter Authentication site

twitter-oauth.png

You can see in an url a redirect_uri. So after sign in Client will get a callback from Twitter with oauth_verifier and oauth_token params

https://api.twitter.com/oauth/authenticate?oauth_token=RcYGqAAAAAAAwdbbAAABVoM1UMo&oauth_token_secret=wZfpPpCugAmdF3AuohEnvBTRxdCmllxu&oauth_callback_confirmed=true&redirect_uri=http://open-event-dev.herokuapp.com/tCallback

The last step is to get an access token. If we have an oauth_verifier and an oauth_token it’s pretty easy

def get_access_token(self, oauth_verifier, oauth_token):

   consumer = self.get_consumer()

   client = oauth2.Client(consumer)

   return client.request(

       self.TW_ACCESS_TOKEN_URI + 'oauth_verifier=' + oauth_verifier + 
       "&oauth_token=" + oauth_token, "POST")

Where TW_ACCESS_TOKEN_URI is https://api.twitter.com/oauth/access_token

Final step is to get our user information

resp, content = client.request("https://api.twitter.com/1.1/users/show.json?
                               screen_name=" + access_token["screen_name"] +
                               "&user_id=" + access_token["user_id"] , "GET")

user_info = json.loads(content)

In an user_info variable you can get a profile picture or a profile name.

Summarizing, oauth protocol is very secure and easy to use by developer. At the beginning an oauth flow can seem to be a little hard to  understand but if you spend some time trying tp understand it, everything becomes easier.  And it’s secured. because you don’t need to store a login or a password, and an access token has an expired time. This is the main feature of Oauth protocol.

Handling data in android

So this week I was working with getting some data from the sqlite database in android and someone who was a beginner in android also asked me to help him with the same. I asked him what he knew and he said that even after reading up a lot he wasn’t able to figure out what exactly to do with the data he wants to save and use in his app. I have seen that this is a problem with a lot of people starting to develop android apps. So, I decided to write a blog on how can you handle your data in your android apps.

Most of the android apps need to save data even if only to save some user preferences. So primarily there are 3 ways to save your data :

  1. In form of key values (SharedPreferences)
  2. Reading/Writing to files
  3. Writing to a database

So let’s go step by step. When we need to store just some preferences of the users like if they want notifications or what kind of theme they want : light or dark etc. So basically if we want to store a key value in the persitant storage of the app we can do that using SharedPreferences. To use sharedpreferences, we initialise the sharedpreference object like

SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);

in oncreate and cache it. Then we just need to add or retrieve what we want using this cached SharedPreferences object. To Add a key value pair :

sharedPreferences.edit().putString("someKey", "someValue").apply();

Also you can put all kinds of stuff here. For example right now we added a string with key “someKey” and Value “someValue”. We can also add Booleans, Floats, Ints, Longs, StringSets etc.

To retrieve the same value we do something like this

sharedPreferences.getString("someKey", "DefaultValue");

Now if you want some logs or some values that can be exported and sent to your server, you should write them to files and maybe read some json inputs etc. as well.

Basically android has a File system similar to other platforms. All android devices have two file storage areas : “Internal” and “external” storage. The difference between them is as follows :

Internal :

  • Always available
  • Files saved here are accesible by only your app
  • When user uninstalls the app, system removes all your app’s files from internal storage

Best to use this when you want to be sure that neither the user nor the other app’s can access your files

External :

  • It’s not always available because user can mount external storage as USB storage and remove it as well
  • It’s readable by anything(Other apps, users etc.)
  • When you uninstall, system removes your app’s files from here only if you save them in the directory from getExternalFilesDir()

Now to read and write files, you need extra permissions

  • android.permission.WRITE_EXTERNAL_STORAGE
  • android.permission.READ_EXTERNAL_STORAGE

So now let’s get down to it. How do I save and read files in my app?

You first initialise the File object

File file = new File(context.getFilesDir(), filename);

This will create a file with filename in the internal storage. For external storage

first check if the storage is available, then just create a file using getExternalStoragePublicDirectory

File file = new File(Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES), albumName);
    if (!file.mkdirs()) {
        Log.e(LOG_TAG, "Directory not created");
    }
    return file;

This is for writing public files.

Now we move onto the most used part in an android app which is a database.Android has a built in SQLite database package which helps us in writing databases in files with syntax similar to SQL.

You need to add 2 classes which are mandatory and another class which basically helps you get organised. So the first is a Contract. This is where you actually write statements that will be executed later on to initialise or create the tables we want. For this make an a static abstract inner class that implements BaseColums like

public static abstract class Microlocation implements BaseColumns {
    public static final String TABLE_NAME = "microlocation";

    public static final String ID = "id";

    public static final String NAME = "name";

    public static final String LATITUDE = "latitude";

    public static final String LONGITUDE = "longitude";

    public static final String FLOOR = "floor";

    public static final String[] FULL_PROJECTION = {
            ID,
            NAME,
            LATITUDE,
            LONGITUDE,
            FLOOR

    };

    public static final String CREATE_TABLE =
            "CREATE TABLE " + TABLE_NAME
                    + " ("
                    + ID + INT_TYPE + PRIMARY_KEY + COMMA_SEP
                    + NAME + TEXT_TYPE + COMMA_SEP
                    + LATITUDE + REAL_TYPE + COMMA_SEP
                    + LONGITUDE + REAL_TYPE + COMMA_SEP
                    + FLOOR + INT_TYPE
                    + " );";

    public static final String DELETE_TABLE = "DROP TABLE IF EXISTS " + TABLE_NAME;


}

Here we are making static final Strings for column names and then creating a static final String CREATE_TABLE which is basically a statement that creates the table Microlocation with the specified key, columns, data types etc.

After adding this structure for all the tables we want to have in our database, we move on to adding a DbHelper class that extends SQLiteOpenHelper which basically has two Abstract methods called onCreate(SQLiteDatabase db) and onUpgrade(SQLiteDatabase db) which are called when the database is created and database version is changed respectively. We call all our CREATE_TABLE static Strings in onCreate which in turn creates all the tables. Something like this :

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(DbContract.Speakers.CREATE_TABLE);
    db.execSQL(DbContract.Sponsors.CREATE_TABLE);
    db.execSQL(DbContract.Sessions.CREATE_TABLE);
    db.execSQL(DbContract.Tracks.CREATE_TABLE);
    db.execSQL(DbContract.Sessionsspeakers.CREATE_TABLE);
    db.execSQL(DbContract.Event.CREATE_TABLE);
    db.execSQL(DbContract.Microlocation.CREATE_TABLE);
    db.execSQL(DbContract.Versions.CREATE_TABLE);
    db.execSQL(DbContract.Bookmarks.CREATE_TABLE);
    db.execSQL(DbContract.EventDates.CREATE_TABLE);
}

You can also call DELETE_TABLE Strings in onUpgrade and the call onCreate again if you like but it’s not compulsory.

Now that you’re database is initialised, let’s add some records into it. For example I have to add a new Micrlocation I’d create a method in my data model where I’ll add a basic structure for the query and then format it with the values for a particular object of the model. Something, like this

public String generateSql() {
    String insertQuery = "INSERT INTO %s VALUES ('%d', %s, '%f', '%f', '%d');";
    return String.format(Locale.ENGLISH,
            insertQuery,
            DbContract.Microlocation.TABLE_NAME,
            id,
            DatabaseUtils.sqlEscapeString(StringUtils.optionalString(name)),
            latitude,
            longitude,
            floor);
}

and then I’d execute the string returned by the call

String query = model.generateSql();

by this

public void insertQuery(String query, DbHelper mDbHelper) {
    SQLiteDatabase db = mDbHelper.getWritableDatabase();
    db.beginTransaction();
    db.execSQL(query);
  
    db.setTransactionSuccessful();
    db.endTransaction();
}

Where db is just a SQLiteDatabase instance.

Now that we have records we want to retrieve them according to usage and for that we create helper methods. This is an example of the retrieving all the microlocations added to the database in ASCENDING order of NAME

public ArrayList<org.fossasia.openevent.data.Microlocation> getMicrolocationsList(SQLiteDatabase mDb) {
    String sortOrder = DbContract.Microlocation.NAME + ASCENDING;
    Cursor cursor = mDb.query(
            DbContract.Microlocation.TABLE_NAME,
            DbContract.Microlocation.FULL_PROJECTION,
            null,
            null,
            null,
            null,
            sortOrder
    );

    ArrayList<org.fossasia.openevent.data.Microlocation> microlocations = new ArrayList<>();
    org.fossasia.openevent.data.Microlocation microlocation;

    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
        microlocation = new org.fossasia.openevent.data.Microlocation(
                cursor.getInt(cursor.getColumnIndex(DbContract.Microlocation.ID)),
                cursor.getString(cursor.getColumnIndex(DbContract.Microlocation.NAME)),
                cursor.getFloat(cursor.getColumnIndex(DbContract.Microlocation.LATITUDE)),
                cursor.getFloat(cursor.getColumnIndex(DbContract.Microlocation.LONGITUDE)),
                cursor.getInt(cursor.getColumnIndex(DbContract.Microlocation.FLOOR))
        );
        microlocations.add(microlocation);
        cursor.moveToNext();
    }
    cursor.close();
    return microlocations;
}

First we create a cursor and then just iterate of the cursor to get microlocation objects and add them to an Arralist and return the Arraylist to the calling method.

So This are most of the things that are there to handling data in Android. Should be sufficient to get you started.

Sorry for the long post but the content couldn’t be made any smaller but I hope you gain something from this post. You can checkout implementations I have followed for the Open event project in the github repo https://github.com/fossasia/open-event-android. You can also write to me anytime on FB, Twitter, Email etc. and I’ll be happy to answer any queries. Adios!

References : 1) developers.android.com

2) https://github.com/fossasia/open-event-android

GET and POST requests

If you wonder how to get or update page resource, you have to read this article.

It’s trivial if you have basic knowledge about HTTP protocol. I’d like to get you little involved to this subject.

So GET and POST are most useful methods in HTTP protocol.

What is HTTP?

Hypertext transfer protocol – allow us to communicate between client and server side. In Open Event project we use web browser as client and for now we use Heroku for server side.

Difference between GET and POST methods

GET – it allows to get data from specified resources

POST – it allows to submit new data to specified resources for example by html form.

GET samples:

For example we use it to get details about event

curl http://open-event-dev.herokuapp.com/api/v2/events/95

Response from server:

Of course you can use this for another needs, If you are a poker player I suppose that you’d like to know how many percentage you have on hand.

curl http://www.propokertools.com/simulations/show?g=he&s=generic&b&d&h1=AA&h2=KK&h3&h4&h5&h6&_

POST samples:

curl -X POST https://example.com/resource.cgi

You can often find this action in a contact page or in a login page.

How does request look in python?

We use Requests library to communication between client and server side. It’s very readable for developers. You can find great documentation  and a lot of code samples on their website. It’s very important to see how it works.

>>> r = requests.get('https://api.github.com/user', auth=('user', 'pass'))
>>> r.status_code
200

I know that samples are very important, but take a look how Requests library fulfils our requirements in 100%. We have decided to use it because we would like to communicate between android app generator and orga server application. We have needed to send request with params(email, app_name, and api of event url) by post method to android generator resource. It executes the process of sending an email – a package of android application to a provided email address.

data = {
    "email": login.current_user.email,
    "app_name": self.app_name,
    "endpoint": request.url_root + "api/v2/events/" + str(self.event.id)
}
r = requests.post(self.app_link, json=data)