I keep getting an NPE when checking for a sqlite table

I keep getting an NPE when checking for a sqlite table - android

I'm trying to check to see if a table exists in and SQLite Database with Android using this in my SQLiteOpenHelper file
// Check to see if a table exists
public boolean isTableExists(String tblName) {
String existQuery = "SELECT name FROM sqlite_master WHERE name ='" + tblName + "' and type='table'";
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(existQuery, null);
if(cursor != null){
cursor.close();
return true;
}
return false;
}
The call from my Activity is
if(db.isTableExists("characters") == false){
Intent p = new Intent("com.tml.rpgtodo.CREATECHARACTER");
startActivity(p);
}
I keep getting a NullPointerException on the row with the if statement. What am I doing wrong?

It sounds like db is null when you call if(db.isTableExists("characters") == false).
I also see that you initialize db inside of "isTableExists()". Is that a different "db"?

Related

Insert if not exists: SQLite

I want to insert data if that headline doesn't exist yet in the database.
This is the error I'm getting for the written query:
near "with": syntax error (code 1): , while compiling: SELECT * FROM movie WHERE headline=Albert Collen
Code:
public boolean Insert(Item item) {
SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM " + TABLE + " WHERE headline=" + item.getName() , null);
if (cursor.moveToFirst()) {
} else {
contentValues.put("name", item.getName());
long result = sqLiteDatabase.insert(TABLE, null, contentValues);
if (result == -1) {
return false;
} else {
return true;
}
}
cursor.close();
sqLiteDatabase.close();
return true;
}

You should use query parameters
rawQuery("SELECT * FROM movie WHERE headline = ?", new String[] {"Albert Collen"});
to avoid having to escape quotes and other chars.

First of all, result query is wrong. All the string constants are to be quoted, like this
SELECT * FROM movie WHERE headline='Albert Collen';
So, try to compose query like this, perhaps it will help
Cursor cursor = sqLiteDatabase.rawQuery("SELECT * FROM " + TABLE + " WHERE headline='" + item.getName() + "'" , null);
But concatenating a query is not a good idea because it makes at least SQL-injections possible.
For example, it can cause problems when item.getName() contains following line "'; drop table movies;"
Better option would be using bind query variables. Unfortunately, I'm not familiar with how to use java-android with sqlite, so it is better for you to check how to use such a queries in android

my sqlite cursor returns empty result for a query

I have a small function for checking to see if a records already exists in my sqlite database. There is data in the database that should match the query, i have verified this by opening up the database.But i get an empty result.
Below is the function, it takes in a parameter and uses that as the search parameter. i have also verified that the parameter is correct.
public boolean checkParent(String email)
{
SQLiteDatabase db = this.getReadableDatabase();
Cursor res = null;
try
{
res = db.rawQuery("SELECT * FROM parents WHERE email = ' " + email + " ' ",null);
res.close();
}
catch (Exception ex)
{
Log.e("Error checking parent", ex.toString());
}
if(res == null)
{
return true;
}
else
{
return false;
}
}

Right way to pass argument in rawQuery method.
db.rawQuery("SELECT * FROM parents WHERE email = ?",new String[]{email});

You are checking whether the cursor object res is null. This will never happen; rawQuery() always returns a cursor object.
You have to check whether the cursor is empty, i.e., whether the cursor actually contains any rows. To do this, call a method like moveToFirst() and check if it succeeds.
Or even better, use a helper function that does handle the cursor for you:
public boolean checkParent(String email)
{
SQLiteDatabase db = this.getReadableDatabase();
long count = DatabaseUtils.queryNumEntries(db,
"parents", "email = ?", new String[]{ email });
return count > 0;
}

Android SQLite check if table exist [duplicate]

I have an android app that needs to check if there's already a record in the database, and if not, process some things and eventually insert it, and simply read the data from the database if the data does exist. I'm using a subclass of SQLiteOpenHelper to create and get a rewritable instance of SQLiteDatabase, which I thought automatically took care of creating the table if it didn't already exist (since the code to do that is in the onCreate(...) method).
However, when the table does NOT yet exist, and the first method ran upon the SQLiteDatabase object I have is a call to query(...), my logcat shows an error of "I/Database(26434): sqlite returned: error code = 1, msg = no such table: appdata", and sure enough, the appdata table isn't being created.
Any ideas on why?
I'm looking for either a method to test if the table exists (because if it doesn't, the data's certainly not in it, and I don't need to read it until I write to it, which seems to create the table properly), or a way to make sure that it gets created, and is just empty, in time for that first call to query(...)
EDIT
This was posted after the two answers below:
I think I may have found the problem. I for some reason decided that a different SQLiteOpenHelper was supposed to be created for each table, even though both access the same database file. I think refactoring that code to only use one OpenHelper, and creating both tables inside it's onCreate may work better...

Try this one:
public boolean isTableExists(String tableName, boolean openDb) {
if(openDb) {
if(mDatabase == null || !mDatabase.isOpen()) {
mDatabase = getReadableDatabase();
}
if(!mDatabase.isReadOnly()) {
mDatabase.close();
mDatabase = getReadableDatabase();
}
}
String query = "select DISTINCT tbl_name from sqlite_master where tbl_name = '"+tableName+"'";
try (Cursor cursor = mDatabase.rawQuery(query, null)) {
if(cursor!=null) {
if(cursor.getCount()>0) {
return true;
}
}
return false;
}
}

I know nothing about the Android SQLite API, but if you're able to talk to it in SQL directly, you can do this:
create table if not exists mytable (col1 type, col2 type);
Which will ensure that the table is always created and not throw any errors if it already existed.

Although there are already a lot of good answers to this question, I came up with another solution that I think is more simple. Surround your query with a try block and the following catch:
catch (SQLiteException e){
if (e.getMessage().contains("no such table")){
Log.e(TAG, "Creating table " + TABLE_NAME + "because it doesn't exist!" );
// create table
// re-run query, etc.
}
}
It worked for me!

This is what I did:
/* open database, if doesn't exist, create it */
SQLiteDatabase mDatabase = openOrCreateDatabase("exampleDb.db", SQLiteDatabase.CREATE_IF_NECESSARY,null);
Cursor c = null;
boolean tableExists = false;
/* get cursor on it */
try
{
c = mDatabase.query("tbl_example", null,
null, null, null, null, null);
tableExists = true;
}
catch (Exception e) {
/* fail */
Log.d(TAG, tblNameIn+" doesn't exist :(((");
}
return tableExists;

Yep, turns out the theory in my edit was right: the problem that was causing the onCreate method not to run, was the fact that SQLiteOpenHelper objects should refer to databases, and not have a separate one for each table. Packing both tables into one SQLiteOpenHelper solved the problem.

// #param db, readable database from SQLiteOpenHelper
public boolean doesTableExist(SQLiteDatabase db, String tableName) {
Cursor cursor = db.rawQuery("select DISTINCT tbl_name from sqlite_master where tbl_name = '" + tableName + "'", null);
if (cursor != null) {
if (cursor.getCount() > 0) {
cursor.close();
return true;
}
cursor.close();
}
return false;
}
sqlite maintains sqlite_master table containing information of all tables and indexes in database.
So here we are simply running SELECT command on it, we'll get cursor having count 1 if table exists.

You mentioned that you've created an class that extends SQLiteOpenHelper and implemented the onCreate method. Are you making sure that you're performing all your database acquire calls with that class? You should only be getting SQLiteDatabase objects via the SQLiteOpenHelper#getWritableDatabase and getReadableDatabase otherwise the onCreate method will not be called when necessary. If you are doing that already check and see if th SQLiteOpenHelper#onUpgrade method is being called instead. If so, then the database version number was changed at some point in time but the table was never created properly when that happened.
As an aside, you can force the recreation of the database by making sure all connections to it are closed and calling Context#deleteDatabase and then using the SQLiteOpenHelper to give you a new db object.

Kotlin solution, based on what others wrote here:
fun isTableExists(database: SQLiteDatabase, tableName: String): Boolean {
database.rawQuery("select DISTINCT tbl_name from sqlite_master where tbl_name = '$tableName'", null)?.use {
return it.count > 0
} ?: return false
}

public boolean isTableExists(String tableName) {
boolean isExist = false;
Cursor cursor = db.rawQuery("select DISTINCT tbl_name from sqlite_master where tbl_name = '" + tableName + "'", null);
if (cursor != null) {
if (cursor.getCount() > 0) {
isExist = true;
}
cursor.close();
}
return isExist;
}

no such table exists: error is coming because once you create database with one table after that whenever you create table in same database it gives this error.
To solve this error you must have to create new database and inside the onCreate() method you can create multiple table in same database.

Important condition is IF NOT EXISTS to check table is already exist or not in database
like...
String query = "CREATE TABLE IF NOT EXISTS " + TABLE_PLAYER_PHOTO + "("
+ KEY_PLAYER_ID + " TEXT,"
+ KEY_PLAYER_IMAGE + " TEXT)";
db.execSQL(query);

i faced that and deal with it by try catch as simple as that i do what i want in table if it not exist will cause error so catch it by exceptions and create it :)
SQLiteDatabase db=this.getWritableDatabase();
try{
db.execSQL("INSERT INTO o_vacations SELECT * FROM vacations");
db.execSQL("DELETE FROM vacations");
}catch (SQLiteException e){
db.execSQL("create table o_vacations (id integer primary key ,name text ,vacation text,date text,MONTH text)");
db.execSQL("INSERT INTO o_vacations SELECT * FROM vacations");
db.execSQL("DELETE FROM vacations");
}

.....
Toast t = Toast.makeText(context, "try... " , Toast.LENGTH_SHORT);
t.show();
Cursor callInitCheck = db.rawQuery("select count(*) from call", null);
Toast t2a = Toast.makeText(context, "count rows " + callInitCheck.getCount() , Toast.LENGTH_SHORT);
t2a.show();
callInitCheck.moveToNext();
if( Integer.parseInt( callInitCheck.getString(0)) == 0) // if no rows then do
{
// if empty then insert into call
.....

Android cursor always returning null

I keep getting the following error
android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 1
I know I have data in the database because a similar query for all the data (rather than a single entry) pulls out a list successfully
Here is my code for the database helper
public class DatabaseHandler extends SQLiteOpenHelper {
...
public Service getMostRecentService() {
SQLiteDatabase db = this.getReadableDatabase();
String selectQuery = "SELECT * FROM " + TABLE_CONTACTS + " ORDER BY " + KEY_ID + " DESC LIMIT 1;";
Cursor cursor = db.rawQuery(selectQuery, null);
Service service = new Service();
if(cursor != null) {
service = new Service(cursor.getString(1), cursor.getString(2));
}
return service;
}
}
Any ideas why I keep getting the out of bounds exception?

You have not positioned your Cursor on a row. Initially, it is at position -1. Presumably, given your existing code, you should call moveToFirst() on the Cursor after the null check and before your getString() calls.

How To check data-base Table to find whether the value is already there?

I am new to android and sqlLite,
I want to prepare code for checking whether the given value in the EditText is already
there in the database table or not?

Try like below:
boolean editTextValue= false;
Cursor cursor = database.rawQuery("SELECT * FROM " + TABLE_NAME, null);
while(cursor.moveToNext()){
String recorded_editTextValue=cursor.getString(cursor.getColumnIndex("editTextValue"));
if(recorded_editTextValue.equals(new_recorded_editTextValue)){
editTextValue= true;
break;
}
}
if(!editTextValue)
// add new_record_editTextValue to database
here: new_recorded_editTextValue is new insert value
recorded_editTextValue is existing value of db

Use following function it will return true if database table contains editext value other vise it will return false
// Please change TableName to your database table in which you want to check value and columnname to your table column in which you are checking
private boolean checkValueFromDatabaseTable() {
DatabaseHelper dbhelp = new DatabaseHelper(getActivity());
SQLiteDatabase db = dbhelp.getReadableDatabase();
Cursor cursor = db.rawQuery("select * from TableName where columnname ='" + edittext.getText().toString() + "'", null);
cursor.moveToFirst();
if (cursor.getCount() != 0)
{
//Means you have matching value in table so return true
return true;
}
else
{
return false;
}
db.close();
db.releaseReference();
dbhelp.close();
}

To check the value from database use this code:
public boolean isFileExist(String edittextValue){
String q="Select column_name from table_name WHERE column_name='"+edittextValue+"'";
Cursor cur=sdb.rawQuery(q, null);
boolean isExist=false;
while(cur.moveToNext()){
isExist=true;
}
cur.close();
return isExist;
}
Just pass your edit text value in argument of this method
If it returns true then value exist or returns false means value does not exist

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

I keep getting an NPE when checking for a sqlite table - android

It sounds like db is null when you call if(db.isTableExists("characters") == false). I also see that you initialize db inside of "isTableExists()". Is that a different "db"?

Related

Insert if not exists: SQLite

my sqlite cursor returns empty result for a query

Android SQLite check if table exist [duplicate]

Android cursor always returning null

How To check data-base Table to find whether the value is already there?

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