Working with the SQLite-Database - Cursors

What you learn:You will learn how tocreatedatabases andtables,insertandquerydatasets in the Android-built-inSQLite-DataBase-Server.

Difficulty:1 of 5

Questions/Problems:Simply post below...

What it will look like:

Description:
We'll need to to the following things:

1. Create a DataBase(generally this is done just once)
2. Open the DataBase
3. Create a Table(generally this is done just once)
4. Insert some Datasets
5. Query for some Datasets
6. Close the Database

0.)So lets work it out:
We first do some setup. Declaring the DataBases/Tables we are using as final should always be preferred before typing the name to every single statement. (Changes are a lot easier !).

Java:

public classDataBaseWork extendsListActivity { private final StringMY_DATABASE_NAME = "myCoolUserDB"; private final StringMY_DATABASE_TABLE = "t_Users"; /** Called when the activity is first created. */ @Override public voidonCreate (Bundle icicle ) { super. onCreate (icicle ); /* Will hold the 'Output' we want to display at the end. */ ArrayListresults = newArrayList ( );

1.)So lets create the DataBase:

Java:

SQLiteDatabase myDB = null; try { /* Create the Database (no Errors if it already exists) */ this. createDatabase (MY_DATABASE_NAME,1,MODE_PRIVATE,null );

2.)Having created the DataBase we want to open it:

Java:

/* Open the DB and remember it */ myDB = this. openDatabase (MY_DATABASE_NAME,null );

3.)Now we create a simple Table with just four columns:

Java:

/* Create a Table in the Database. */ myDB. execSQL ( "CREATE TABLE IF NOT EXISTS " + MY_DATABASE_TABLE + " (LastName VARCHAR,FirstName VARCHAR," + " Country VARCHAR,Age INT(3));" );

4.)Put two DataSets to the recently created Table:

Java:

/* Add two DataSets to the Table. */ myDB. execSQL ( "INSERT INTO " + MY_DATABASE_TABLE + " (LastName,FirstName,Country,Age)" + " VALUES ('Gramlich','Nicolas','Germany',20);" ); myDB. execSQL ( "INSERT INTO " + MY_DATABASE_TABLE + " (LastName,Age)" + " VALUES ('Doe','John','US',34);" );

5.)Having written some DataSets to the Table,we would want to receive them back somewhen. Thr result of a query is a Cursor that can move over all the results returned by the query. We apply Projection (Just the Specified Columns) and Selection (WHERE ...) to it and a LIMIT. Just as we would do in any other SQL-"Dialect":

Java:

/* Query for some results with Selection and Projection. */ Cursorc = myDB. query ( "SELECT FirstName,Age"+ " FROM "+ MY_DATABASE_TABLE + " WHERE Age > 10 LIMIT 7;", null );

6.)Now having queried,we retrieve the ColumIndexes of two Columns calling thegetColumnIndex(String);-method of the Cursor:

Java:

/* Get the indices of the Columns we will need */ intfirstNameColumn = c. getColumnIndex ( "FirstName" ); intageColumn = c. getColumnIndex ( "Age" ); /* Check if our result was valid. */ if (c != null ) { /* Check if at least one Result was returned. */ if (c. first ( ) ) { inti = 0; /* Loop through all Results */ do { i++; /* Retrieve the values of the Entry * the Cursor is pointing to. */ StringfirstName = c. getString (firstNameColumn ); intage = c. getInt (ageColumn ); /* We can also receive the Name * of a Column by its Index. * Makes no sense,as we already * know the Name,but just to shwo we can*/ StringageColumName = c. getColumnName (ageColumn ); /* Add current Entry to results. */ results. add ( ""+ i + ": "+ firstName + " ("+ ageColumName + ": "+ age + ")" ); } while (c. next ( ) ); } }

7.)Finally close the DataBase (if it has been opened):

Java:

} catch ( FileNotFoundExceptione ) { } finally { if (myDB != null ) myDB. close ( ); }

8.)In the end,display our Entries:

Java:

this. setListAdapter ( newArrayAdapter ( this, android. R. layout. simple_list_item_1_small,results ) ); } }