catch error when user is trying to insert duplicated value in database - greenDAO

Question

im using greenDAO to generate my DAO classes, everything works fine till i try to insert duplicated values for primary key.

It fails when i try to insert duplicated primery key (as expected), but i would like to send the exception to the user and not o explode with the app.

For now the only solution i have, and i think its not the best, is to do a query before insert, and check if the result count is greater than 0 or not.

There is a better way to do it?

the method .insert returns a Long value, but when it fails to insert it doesn't return anything, just explodes with the app.

Answer 1

I thought it would be another way to control it, but i found my way without doing this SELECT. Here are two solutions:

1. With SELECT

With SELECT (proposed by other user on this post - check it for more details)

public int getPrimaryId() {
        final String MY_QUERY = "SELECT MAX(_id) FROM " + DATABASE_TABLE0;
        Cursor cur = mDb.rawQuery(MY_QUERY, null);
        cur.moveToFirst();
        int ID = cur.getInt(0);
        cur.close();
        return ID;
    }

1. Override method

   Override .insert() method, inside myObjectDAO.java

@Override
  public long insert(Stud_Course entity) {
      long ret = 0;
      try {
          ret = super.insert(entity);
      } catch (Exception e) {
          ret = 0;
          Log.e("LOG", "fail to insert!!!");
      }
      return ret;
  }

Answer 2

Best would be to keep your primary key incremental away from what the user supplies as a key. However that is my personal choice, but aids when I have to check the last inserted ID, Ill do something like:

public int getPrimaryId() {
        final String MY_QUERY = "SELECT MAX(_id) FROM " + DATABASE_TABLE0;
        Cursor cur = mDb.rawQuery(MY_QUERY, null);
        cur.moveToFirst();
        int ID = cur.getInt(0);
        cur.close();
        return ID;
    }

In your case you can preload an array list with primaryID's once user supplies a new key just check it with the elements in the arraylist. Faster!

Update: To Check if ID exists.

SELECT EXISTS(SELECT 1 FROM myTbl WHERE ID="anyID" LIMIT 1);

The LIMIT will ensure that once found there is no need to go further. This would be super fast. Plus Exists will always return a result.

Also suggested would be the use of proper indexes

Answer 3

Surround your insert-statement with a try-catch-block

try {
    dao.insert (entity);
} catch (Exception ex) {
    // Do your handling here
} catch (Error e) {
    // and here
}