Realm Auto Increament field example

问题

I need to add auto increment key field in Realm database in android. how can i do this? Is this possible?

Thanks in advance.

回答1:

Relam currently doesn't support auto_increment

see this issue on GitHub

you can take work around like this

realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
         // increment index
         Number num = realm.where(dbObj.class).max("id");
         int nextID;
         if(num == null) {
            nextID = 1;
         } else {
            nextID = num.intValue() + 1;
         }
         dbObj obj = realm.createObject(dbObj.class, nextID);
         // ...
    }
}

回答2:

The Java binding does not support primary keys yet, but it's on the roadmap and with high priority - see: https://groups.google.com/forum/#!topic/realm-java/6hFqdyoH67w . As a workaround you can use this piece of code for generating keys:

int key;
try {
  key = realm.where(Child_pages.class).max("id").intValue() + 1;
} catch(ArrayIndexOutOfBoundsException ex) {
 key = 0; // when there is no object in the database yet
}

I use singleton factory for generating primary keys as a more generic solution with better performance (no need to query for max("id") every time).

There is a long discussion in Realm Git Hub if you need more context: Document how to set an auto increment id?

来源：https://stackoverflow.com/questions/31229226/realm-auto-increament-field-example