Sqlite_for _android : Contains Steps , solution for Errors that I faced while implementing it in projects

Steps on how to install sqlite:

• Download sqlite-tools-win32-*.zip from this link: https://www.sqlite.org/download.html
• Once you’ve downloaded this zip, open up Windows explorer and navigate to your C:\ drive. Once there, create a folder called sqlite. Copy the .zip file you just downloaded into this folder and then extract its contents.
• Once you’ve done that, you’ll need to add C:\sqlite to your system’s PATH environment variable. Finally, you’ll need to open your command prompt program and type in sqlite3, then hit enter.
• Video Link : https://www.youtube.com/watch?v=zOJWL3oXDO8

Procedure :

1. Define a schema & a contract
2. Create a database using SQL HELPER
3. Add a cursor to it
4. Use content provider
5. Use cursor loader
6. Use content URI
7. Use URI matcher
8. Sanity checking
9. Implement contentprovider[MIME Type]

Why we need Contract class :

• To define constants used in the Database.
• To avoid spelling errors.
• Ease of updating schema.

Contract class contains :

• Outer class.
• Inner class.
• String constants.

Use of SQLiteOpenHelper :

• Create a sqliteDB.
• Gives a connection to the DB.
• Manages updating DB schema if version changes.

How to implement SQLiteOpenHelper :

1. Create a class that extends from SQLiteOpenHelper
2. Create constants for DBnames & DBversions
3. Create a constructor
4. Implement onCreate() method
5. Implement onUpgrade() method

Getting a database connection :

• use SQLiteDatabase db = mDbHelper.getReadableDatabase();
• mDbHelper is an instance of SQLiteOpenHelper which will look for the Database , If a DB doesnot exist it will create a new DB using onCreate() method.

Cursor :

• A cursor is an object that represents a bunch of rows in a database . https://developer.android.com/reference/android/database/sqlite/SQLiteDatabase#query(java.lang.String,%20java.lang.String[],%20java.lang.String,%20java.lang.String[],%20java.lang.String,%20java.lang.String,%20java.lang.String)

Acessing sqlite3 database in Androidstudio :

Use of Content provider :

• Inorder to eliminate the direct interaction of the UI with DB , we use content provider .
• Doesnot allow the invalid data to enter the database .
• Good abstraction layer between the data source & the UI code

• Works well with other android framework classes , For an instance:Activity manager

• https://developer.android.com/guide/topics/providers/content-provider-basics

Use of Cursor loader :

• The cursor loader will check when any new data is added or removed in the list to keep the list updated
• It also checks the data and updates it
• So the cursor loader works in conjuction with the listView & the cursor adapter
• Loader that queries the ContentResolver with a specific URI & returns a Cursor
• Loads data on a background thread because reading & writing to a database can be an expensive operation
• works well with content provider because a loader is tied to a URI
• Inorder to implement the Cursor loader we requires Content provider

Activities to be done to implement a Cursor loader :

1. onCreate()[getLoaderManager().initLoader()]
2. onCreateLoader()
3. onLoadFinished()[use swapCursor(cursor) in this method]
4. onLoaderReset()[use swapCursor(null) in this method]
   • https://developer.android.com/reference/android/widget/CursorAdapter?utm_source=udacity&utm_medium=course&utm_campaign=android_basics

How does other app access database of an another app :

• The external app uses a Content URI to give a request to the Contacts provider of the required app

How does the Content URI matches with correct content provider :

• The content Resolver does this work
  • The content URI(content://com.android.contacts/contacts/2) will be passed to the content Resolver
    • Based on the content authority (i.e: com.android.contacts) the content resolver will handle the data and send to ContactsProvider.
    • To allow the external apps to access the database we should give android:exported=”true” in the manifest file
• https://www.androiddesignpatterns.com/2012/06/content-resolvers-and-content-providers.html
• https://www.grokkingandroid.com/android-tutorial-writing-your-own-content-provider/

Use of Content URI :

• can point to a part of a database
• can point to a file(text,images etc..)
• In this content URI content://com.android.contacts/contacts/2
  • content:// - refers to schema
  • com.android.contacts - refers to Content Authority(Unique for each content provider)
  • contacts - refers to Type of data (table name should be given here)
  • 2 - refers to specific rows in the table(inorder to derive a single row)

Why URI matcher is needed :

• Helps us to ensure that the Contentprovider doesn’t try to handle unexpected content URIs

Steps to create a URI matcher :

• Setup the URI matcher with the URI patterns your content provider will accept & assign each pattern an integer code
• Call UriMatcher.match(uri) and pass in a uri , which will return the corresponding integer code (if matched)

Sanity checking :

• https://developer.android.com/reference/android/content/ContentValues?utm_source=udacity&utm_medium=course&utm_campaign=android_basics

Why to declare MIME Type :

• the getType(Uri uri) method. The purpose of this method is to return a String that describes the type of the data stored at the input Uri. This String is known as the MIME type, which can also be referred to as content type.
• The Android system will check the MIME type of that URI to determine which app component on the device can best handle your request.
• https://stackoverflow.com/questions/7157129/what-is-the-mimetype-attribute-in-data-used-for

Implement this [method] to handle requests for the MIME type :

• The returned MIME type should start with “vnd.android.cursor.item” for a single record, or “vnd.android.cursor.dir/” for multiple items.
• Step 1: Declare MIME Type constants in Contract.java file
• Step 2: Implement ContentProvider getType() method

Related to UI :

• Populating a listview with a cursor adapter
• check this :https://github.com/codepath/android_guides/wiki/Populating-a-ListView-with-a-CursorAdapter

Error:class or interface expected:

• when there is an error as class or interface expected it can be cleared by removing the curly brace on where it is showing a hint as an error

Projects done using Sqlite:

• https://github.com/thirulak/Project8
• https://github.com/thirulak/Project9

Web links :

• https://developer.android.com/training/data-storage/sqlite#java
• https://developer.android.com/training/data-storage/room/
• https://stackoverflow.com/questions/20291307/correct-way-to-trim-a-string-in-java
• https://developer.android.com/guide/topics/data/data-storage
• https://en.wikipedia.org/wiki/SQL_injection
• https://developer.android.com/reference/android/database/Cursor
• https://developer.android.com/reference/android/content/ContentResolver
• https://developer.android.com/guide/topics/providers/contacts-provider
• https://developer.android.com/guide/topics/manifest/provider-element?utm_source=udacity&utm_medium=course&utm_campaign=android_basics
• https://developer.android.com/guide/topics/providers/content-provider-creating#ContentURI
• https://developer.android.com/reference/android/content/UriMatcher
• https://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html

Code reference :

• https://github.com/codepath/android_guides/wiki/Local-Databases-with-SQLiteOpenHelper

Sql injection : https://www.netsparker.com/blog/web-security/sql-injection-vulnerability/