building web applications

The best method to use when building web applications is to use frameworks. Frameworks save on time and adhere to the principle of not repeating code all the time (DRY). So if you decide to use a framework, what should your choice be.There are many frameworks out there and therefore it would not be okay just to point you to one.To gain a deeper understanding of building web applications using frameworks it is advisable to go down the path of discovery.

1. Pick a framework based on any language you know of and learn it, this should be the beginning.
2. After taking a week or two to learn the new framework, do a side project with it, not a serious one but something far from the basics.Try to implement some idea you've always had.
3. Add the side project to your portfolio and start over again from step 1 this time with another framework which is related.

After going through the first iteration, try implement the idea you had done using the new framework you have just learned.This aids you in discovering weaknesses and strengths in a framework.

Be patient
Nothing comes easy, everything requires time and effort, so don't expect to excel at it immediately.With continuous practice and diligent effort you will notice your skills and knowledge increasing.
I wish to stress the importance of persistence here.It's what will bear the results.

Django Tastypie with android client part 2

This post picks up from part 1 where we had defined the api using tastypie.The purpose of this second part is to create an android client to consume the api. here are the files that make up the android application. RecipesActivity.java

package com.thecodachi.recipe;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.List;

import org.apache.http.HeaderElement;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.ParseException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.protocol.HTTP;

import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import com.j256.ormlite.android.apptools.OpenHelperManager;
import com.j256.ormlite.dao.Dao;

import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class RecipesActivity extends Activity {
 
 public static String api_url = "http://10.0.2.2:8000/api/";
 
 private List recipesList = null;
 private ProgressDialog progDialog;
 private ProgressThread progThread;
 private ListView recipes;

 private DatabaseHelper databaseHelper = null;

 private ArrayAdapter adapter;
 
 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        recipes = (ListView)findViewById(R.id.lvRecipes);
        
        showDialog(0);
  
        try{
   //get our Dao and query for all customers in db
   Dao recipes = getHelper().getRecipeDataDao();
   recipesList = recipes.queryForAll();
  
  }catch(SQLException e){
   Log.e("LOG", "error getting products");
  }
  
  
        adapter = new ArrayAdapter(this,
                      R.layout.recipe_row,
                      R.id.recipeLabel,
                      recipesList);
        recipes.setAdapter(adapter);
    }

 @Override
 protected Dialog onCreateDialog(int id) {
  switch(id){
  case 0:
   progDialog = new ProgressDialog(this);
   progDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
   progDialog.setMessage("Loading data...");
   progThread = new ProgressThread();
            progThread.start();
   return progDialog;
  default:
   return null;
  }
 }
 
 private class ProgressThread extends Thread{
  
  private static final String LOG_TAG = "PROGRESS_THREAD";

  @Override
  public void run() {
   HttpClient httpClient = new DefaultHttpClient();
   HttpGet httpGet = new HttpGet(api_url+"recipes/?format=json&limit=0");
   HttpResponse response = null;
   try{
    
    response = httpClient.execute(httpGet);
    
   }catch(Exception e){
    System.out.println(e.toString());
   }
   if(response!=null){
    HttpEntity entity = response.getEntity();
    String apiResponse = null;
    try {
     apiResponse = _getResponseBody(entity);
    } catch (ParseException e) {
     e.printStackTrace();
    } catch (IOException e) {
     e.printStackTrace();
    }
    if(apiResponse!=null){
     try{
      Dao recipesDao = getHelper().getRecipeDataDao();
      
      JsonElement json = new JsonParser().parse(apiResponse);
      JsonObject rootObject = json.getAsJsonObject();
      JsonArray array= rootObject.getAsJsonArray("objects");
      Iterator iterator = array.iterator();
      
      while(iterator.hasNext()){
       JsonElement json2 = (JsonElement)iterator.next();
       Gson gson = new Gson();
       Recipe recipe = gson.fromJson(json2, Recipe.class);
       recipesDao.createIfNotExists(recipe);
       Log.d(LOG_TAG, "--------------------------------created recipe");
      }
      
     }catch(Exception e){
      Log.e(LOG_TAG, "error creating recipe from json");
     }


    }
    
   }  
   dismissDialog(0);
   adapter.notifyDataSetChanged();
  }
 }
 public static String _getResponseBody(final HttpEntity entity) throws IOException, ParseException {

  if (entity == null) { throw new IllegalArgumentException("HTTP entity may not be null"); }

  InputStream instream = entity.getContent();

  if (instream == null) { return ""; }

  if (entity.getContentLength() > Integer.MAX_VALUE) { throw new IllegalArgumentException(

  "HTTP entity too large to be buffered in memory"); }

  String charset = getContentCharSet(entity);

  if (charset == null) {

  charset = HTTP.DEFAULT_CONTENT_CHARSET;

  }

  Reader reader = new InputStreamReader(instream, charset);

  StringBuilder buffer = new StringBuilder();

  try {

  char[] tmp = new char[1024];

  int l;

  while ((l = reader.read(tmp)) != -1) {

  buffer.append(tmp, 0, l);

  }

  } finally {

  reader.close();

  }

  return buffer.toString();

  }
 public static String getContentCharSet(final HttpEntity entity) throws ParseException {

  if (entity == null) { throw new IllegalArgumentException("HTTP entity may not be null"); }

  String charset = null;

  if (entity.getContentType() != null) {

  HeaderElement values[] = entity.getContentType().getElements();

  if (values.length > 0) {

  NameValuePair param = values[0].getParameterByName("charset");

  if (param != null) {

  charset = param.getValue();

  }

  }

  }

  return charset;

  }
 private DatabaseHelper getHelper(){
  if(databaseHelper  == null){
   databaseHelper = OpenHelperManager.getHelper(this, DatabaseHelper.class);
  }
  return databaseHelper;
 }
}

Recipe.java class which defines a recipe object which can be persisted in the sqlite database using ormlite.

package com.thecodachi.recipe;

import com.j256.ormlite.field.DatabaseField;

public class Recipe {
 
 @DatabaseField(id=true)
 private int id;
 
 @DatabaseField
 private String name;
 
 @DatabaseField
 private String content;
 
 Recipe(){
  //used by ormlite
 }
 
 
 public int getId() {
  return id;
 }


 public void setId(int id) {
  this.id = id;
 }


 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 public String getContent() {
  return content;
 }

 public void setContent(String content) {
  this.content = content;
 }


 @Override
 public String toString() {
  // TODO Auto-generated method stub
  return name;
 }
 
}

DatabaseHelper.java responsible for persisting and retreiving objects from sqlite database using ormlite.

package com.thecodachi.recipe;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

import com.j256.ormlite.android.apptools.OrmLiteSqliteOpenHelper;
import com.j256.ormlite.dao.Dao;
import com.j256.ormlite.support.ConnectionSource;
import com.j256.ormlite.table.TableUtils;

public class DatabaseHelper extends OrmLiteSqliteOpenHelper {

 //name of the database file for the application
 private static final String DATABASE_NAME = "Recipe.db";
 private static final int DATABASE_VERSION = 1;
 /*
  * the DAO objects we use to access the recipes* 
  */
 
 private Dao recipesDao = null;
 
 public DatabaseHelper(Context context){
  super(context, DATABASE_NAME, null, DATABASE_VERSION);
 }
 
 @Override
 public void onCreate(SQLiteDatabase db, ConnectionSource connectionSource) {
  try{
   Log.i(DatabaseHelper.class.getName(), "onCreate");
   
   TableUtils.createTable(connectionSource, Recipe.class);
 
   
  }catch(java.sql.SQLException e){
   Log.e(DatabaseHelper.class.getName(),"can't create db");
   throw new RuntimeException();
  }
 }

 //called when your application is upgraded
 
 @Override
 public void onUpgrade(SQLiteDatabase db, ConnectionSource connectionSource, int oldVersion,
   int newVersion) {
  try{
   Log.i(DatabaseHelper.class.getName(), "onUpgrade");
   TableUtils.dropTable(connectionSource, Recipe.class, true);
   
   //after dropping old databases, we create the new ones
   onCreate(db, connectionSource);
   
  }catch(java.sql.SQLException e){
   Log.e(DatabaseHelper.class.getName(), "can't drop databases");
   throw new RuntimeException(e);
  }
 }
 

 /* methods that returns the Database access object(Dao) for our product class
  * will create it or just give the cached value
  */
 
 public Dao getRecipeDataDao() throws java.sql.SQLException{
  if(recipesDao == null){
   recipesDao = getDao(Recipe.class);
  }
  return recipesDao;
 }


 /*
  * close all database connections and clear any cached DAOs
  */
 @Override
 public void close(){
  super.close();
  recipesDao = null;
 }
}

You can take a look at the rest of the resources belonging to this app from the repo which i will share. The implementation of the REST architecture i took in this example is not the best and it is highly recommended not to use this approach when building an android application.The reason for this is that the app does network requests within an activity.This should be done within a service For a more detailed and recommended architecture for creating RESTful android application look here. Otherwise this is just a demo.

Django Tastypie with android client

I've been using django-tastypie recently to create restful apis and i wanted to use it especially with an android client. I've put together a sample application, django rest backend and an android client to demonstrate this. So here is a quick walk through of the code. Here is the models.py which describes a recipe.

from django.db import models

class Recipe(models.Model):
    name = models.CharField(max_length=50)
    content = models.TextField()

    def __unicode__(self):
        return self.name

We set up a Resource for our API using tastypie.

from tastypie.resources import ModelResource
from recipes.models import Recipe

class RecipeResource(ModelResource):
    class Meta:
 queryset = Recipe.objects.all()
        resource_name = 'recipes'
 allowed_methods = ['get']
        include_resource_uri = False

    def alter_list_data_to_serialize(self, request, data_dict):
        if isinstance(data_dict, dict):
            if 'meta' in data_dict:
                #Get rid of the meta object                                                                               
                del(data_dict['meta'])

        return data_dict

Now we set up the urlpattern to access the data

from django.conf.urls.defaults import patterns, include, url
from recipes.api.api import RecipeResource
from django.contrib import admin
admin.autodiscover()

recipe_resource = RecipeResource()

urlpatterns = patterns('',
    url(r'^api/', include(recipe_resource.urls)),
    url(r'^admin/', include(admin.site.urls)),
)

Test the api using curl.

$ curl -H 'Accept: application/json' http://localhost:8000/api/recipes/

Now that the api works as expected the next part is to create an android app client to consume the api. This will be a simple app for viewing recipes.Later we will add the ability to add recipes to our recipe database from the android client. This will be covered in part 2 of this tutorial.

It's okay to leave if things are not as expected

Lately i have been reading a series of articles about individuals who are leaving or have left their former places of  employment and giving their reasons for leaving.It is very interesting to note that most express dislike about the way things were being steered by their former companies.What is being brought out is that these big companies had turned evil and deviated from their original well meaning motives, if they ever existed.

For one, i tend to think that this is natural.In the world there exists no organisation with an altruistic motive.To think of it, the golden rule is always "whats in it for me".What is actually happening is that eager graduates are drawn in to companies thinking that they are contributing to a greater good, only to realize this years later.Of course there's the usual bouts of philanthropy that usually exist, but deep down to the core, profit is the main motivation.

Startup founders are encouraged to formulate brilliant ideas by looking for problems to solve, or scratching common itches.Ones success is achieved, it all becomes about maximizing profits.Soon the users needs are swept aside.The outlook currently is that the future is in startups, but remember too that the big corporations which have turned evil were once startups.Inevitably as a startup grows into a large  company, moral decay starts occuring.This comes with size and does not occur within a close tightly knit community around a startup because everybody knows everybody and there is close interaction.

There exists a theory in the field of Organization management that brings out this aspect, that as an organization grows it becomes more and more unstable.so it's expected.

Data access on android made easy with OrmLite

OrmLite is a wonderful Object Relational Mapper available for the android operating system.

If your using the normal methods to access the sqlite database, then you are bound to find the
process very tedious.I realized i needed an orm when i found myself writing redundant code and it came to my attention that i was actually writing my own orm.

OrmLite is suited for android because it is lightweight and therefore easy to import to an android project.
Furthermore it uses java annotations to mark classes to be persisted which make your code look clean and easier to understand.

import com.j256.ormlite.field.DatabaseField;

public class Customer {

 @DatabaseField
 int id; 

 @DatabaseField
 String name;

 @DatabaseField
 String country;

 @DatabaseField
 String phone;

 @DatabaseField
 String address;

 @DatabaseField
 String businessName;


 Customer(){
  //used by ormlite
 }

 @Override
 public String toString(){
  return this.name;
 }

}

To create a table we use TableUtils' createTable method

TableUtils.createTable(connectionSource, Customer.class);

Data access is done using Daos(Data access Object),these offer convenient methods for querying, creating, deleting... objects on the sqlite database

private Dao<Customer, Integer> customersDao = getDao(Customer.class);

customersDao.create(customer);


customersDao.delete(customer);

customersDao.queryForAll();

In conclusion, using ormlite saves more time and is more convenient.

Transaction management in django

ACID refers to an acronym in the database transactions.Which in full means.Atomic, Consistent, Independent, Durable(or atomicity, consistency, independency and durability).

Atomicity here refers to the idea that a transaction commits(goes through) as a whole or does not commit at all(all or nothing).Various scenarios necessitate the need to maintain atomicity in a transaction.

For instance if you are creating objects which require foreign key relationships with other objects.
It may be necessary to create the object it is related to on the fly and save it just to make sure the foreign key attribute is satisfied.

when controlling transaction management in views the best approach is to use decorators

from django.db import transaction

@transaction.commit_on_success
def viewfunc(request):
    # ...
    # this code executes inside a transaction
    # ...

There are three types of decorators, autocommit, commit_on_success and commit_manually.
autocommit does django's default commit behaviour
commit_on_success does a single transaction for all the work done in a function, this can be the view function.
commit_manually lets you control transactions manually by calling commit() and rollback().

Care should be taken when using commit manually() because some transactions may occur in unexpected places which require a commit.This raises an exception in django.

A point to note is that some databases do not support transaction management.It is surprising to note that SQLite db supports transactions while MySQL db does not.

programming is all about experience

Having spent a couple of years coding and exploring this industry i tend to think the major factor that influences ones proficiency in coding is experience.

Having experience guarantees that you have made certain mistakes that everybody must make in order to become a professional.It also guarantees that you have tried out solutions to some common problems encountered every day,have encountered the common design patterns that exist for creating software and have tried out the major flavors of programming.

There is the common rule that to master any craft you have to spend 10,000 hours at it, which also tends to stress the importance of experience.