CODEWITHSUNDEEP
androidsqlitenullpointerexception
Maksim Dmitriev
Maksim Dmitriev

Reputation: 6209

SQLite INNER JOIN throws a NullPointerException

I can't understand why the query ends up throwing a NullPointerException.

My database contains two tables. The first one called TABLE_WORDS contains words; the second one called TABLE_TRANS contains the translations. One word can have many translations.

public static final String CREATE_TABLE_WORDS = "CREATE TABLE " + TABLE_WORDS + 
    " (" + WORDS_ID + " INTEGER PRIMARY KEY, " + WORDS_WORD + 
    " TEXT);";

public static final String CREATE_TABLE_TRANS = "CREATE TABLE " + TABLE_TRANS + 
    " (" + TRANS_ID + " INTEGER PRIMARY KEY, " + 
    TRANS_WORD + " TEXT, " + 
    TRANS_FOREIGN_ID_WORD + " INTEGER, " +
    "FOREIGN KEY (" + TRANS_FOREIGN_ID_WORD + ") REFERENCES " + TABLE_WORDS + "(" + WORDS_ID + "));";

I query translations by a word ID, and an NPE is thrown.

public Cursor queryTransesByWord(int idSend) {

    String query = "SELECT " + DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_WORD + ", " +
        DbHelper.TABLE_TRANS + "." + DbHelper.TRANS_WORD + 
        " FROM " + DbHelper.TABLE_WORDS + 
        " INNER JOIN " + DbHelper.TABLE_TRANS + 
        " ON " + DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_ID + "=" + 
        DbHelper.TABLE_TRANS + "." + DbHelper.TRANS_FOREIGN_ID_WORD + " WHERE " +
        DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_ID + "="+ idSend; 

    Cursor cur = db.rawQuery(query, null); // NullPointer always throws here

    if (cur != null)
        cur.moveToFirst();
    else
        Log.e(Constants.LOG_TAG, Constants.DB_ADAPTER_CLASS_NAME_SEP + "queryTransesByWord cursor is null");
    return cur;
}

Upvotes: 2

Views: 1327

Answers (3)

Eng. Gathecha
Eng. Gathecha

Reputation: 11

String query = "SELECT " + DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_WORD + ", " +
DbHelper.TABLE_TRANS + "." + DbHelper.TRANS_WORD + 
" FROM " + DbHelper.TABLE_WORDS + 
" INNER JOIN " + DbHelper.TABLE_TRANS + 
" ON " + DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_ID + "=" + 
DbHelper.TABLE_TRANS + "." + DbHelper.TRANS_FOREIGN_ID_WORD + " WHERE " +
DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_ID + "=?";    

Cursor cur = db.rawQuery(query, new String[] { Integer.toString(idSend) } );

this works for me:-)

Upvotes: 1

Maksim Dmitriev
Maksim Dmitriev

Reputation: 6209

In my case I should use 

String query = "SELECT " + DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_WORD + ", " +
    DbHelper.TABLE_TRANS + "." + DbHelper.TRANS_WORD + 
    " FROM " + DbHelper.TABLE_WORDS + 
    " INNER JOIN " + DbHelper.TABLE_TRANS + 
    " ON " + DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_ID + "=" + 
    DbHelper.TABLE_TRANS + "." + DbHelper.TRANS_FOREIGN_ID_WORD + " WHERE " +
    DbHelper.TABLE_WORDS + "." + DbHelper.WORDS_ID + "=?";    

Cursor cur = db.rawQuery(query, new String[] { Integer.toString(idSend) } );

Am I right?

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1504062

Well, given your code:

Cursor cur = db.rawQuery(query, null); // NullPointer always throws here

That suggests that db is null. There's no other dereferencing operation in that statement - so unless the stack trace actually shows rawQuery in it somewhere, then db is null. You haven't given any indication of where db is meant to be assigned a non-null value, but that's the first thing to check...

As an aside, please don't include values in your SQL like that - it's a recipe for SQL injection attacks. Use parameterized SQL instead.

Upvotes: 4

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