Deleting from a ContentProvider?

Question

I want to delete the first item in my content provider. I'm trying to do this by deleting the row with id 0 (as shown below). This does not work--the app will not run with this code.

public void onClickDeleteExercise(View view){
    int ret_val = getContentResolver().delete(MyProvider.CONTENT_URI, MyProvider.id+ " = ? ", new String[]{"0"});
    Toast.makeText(getBaseContext(), "First exercise deleted", Toast.LENGTH_LONG).show();
}

My provider has defined these:

static final String PROVIDER_NAME = "com.example.contentproviderexample.MyProvider";
static final String URL = "content://" + PROVIDER_NAME + "/cte";
static final Uri CONTENT_URI = Uri.parse(URL);

static final String id = "id";
static final String name = "name";
static final int uriCode = 1;

How would I go about deleting from this? Thank you!!

Answer 1

app:

getContentResolver().delete(Provider.CONTENT_URI,Provider._ID + "=" + id, null);

provider:

public static final Uri BASE_URI = Uri.parse("content://" + AUTHORITY + "/")

public static final Uri CONTENT_URI = Uri.withAppendedPath(BASE_URI,
        ENTRIES_TABLE_NAME);

public static final String _ID = "_id";

@Override
public int delete(Uri uri, String where, String[] whereArgs) {
    database.delete(ENTRIES_TABLE_NAME, where, whereArgs);
    return 0;
}

hint:

• to exclude errors if u use android studio make breakpoint on

  public int delete(..) {
      database.delete() <=  here breakpoint
   }
  

and see if after execute in app getContentResolver() the debugger will move you to this breakpoint

• if it fails u have not registered content provider properly
• if u will hit breakpoint implementation of database.delete is incorect

If I want to delete the first item, would I just set id to 0?

depends if your _id is PRIMARY_KEY in table

• SQlite database Engine has a mechanism that creates a unique ROWID for every new row you insert.

• if you table have a PRIMARY_KEY then it will eventually becomes the alias for that ROW_ID

  class SQLiteDatabase 
  
  /**
   * Convenience method for deleting rows in the database.
   *
   * @param table the table to delete from
   * @param whereClause the optional WHERE clause to apply when deleting.
   *            Passing null will delete all rows.
   * @param whereArgs You may include ?s in the where clause, which
   *            will be replaced by the values from whereArgs. The values
   *            will be bound as Strings.
   * @return the number of rows affected if a whereClause is passed in, 0
   *         otherwise. To remove all rows and get a count pass "1" as the
   *         whereClause.
   */
   public int delete(String table, String whereClause, String[] whereArgs) {}
  

so to pas id as int u need:

database.delete(TABLE_NAME, KEY_ID + " = ?",new String[]{Long.toString(id)});

or simple:

String[] whereArgs = new String[] {String.valueOf(rowId)};

Caution: Rowids will change when the db is vacuumed

So please take extra care when you define a table and need to reference records using rowids.

From the official documentation:

“Rowids can change at any time and without notice. If you need to depend on your rowid, make it an INTEGER PRIMARY KEY, then it is guaranteed not to change”.

• add also AUTOINCREMENT so you are sure that the same rowid(s) are not reused when rows are deleted.

In one of my tables

I got key message_id and it is beginning from value = 1

• If u not sure about Key Value use on Android device SQLIte Debugger very excellent app