greenrobot/greenDAO · error · DaoException

This operation only works with cached lazy lists

Error message

This operation only works with cached lazy lists

What it means

greenDAO's LazyList can operate in two modes: with an eagerly-loaded entity cache (entities != null) or fully lazy, backed only by the cursor. Operations like loadRemaining() and subList() require random access to already-loaded entities, so they throw this DaoException when the list was created without caching. The check is a guard in LazyList.checkCached() protecting operations that cannot be satisfied lazily.

Solutions

1. Use the cached list: call query.list() (or lazyList() only when you truly stream via iterator) instead of calling subList/loadRemaining on the lazy list.
2. If you need partial loading with caching, iterate with get()/peek() on the LazyList instead of subList().
3. Copy needed items into a plain ArrayList by iterating the LazyList, then use subList on that copy.

Example fix

// before
LazyList<User> lazy = query.listLazy();
List<User> page = lazy.subList(10, 20); // DaoException
// after
List<User> all = query.list();
List<User> page = all.subList(10, 20);

LazyList<User> l = query.listLazyUncached();
boolean ok = !(needsSubList || needsLoadRemaining); // avoid these ops on uncached lazy lists

try { page = lazyList.subList(from, to); } catch (DaoException e) { page = query.list().subList(from, to); }

When it happens

Trigger: Calling loadRemaining() or subList() on a LazyList obtained from a query that was not built with caching — i.e. Query.forCurrentThread(...)/lazyList() where the query does not use setForThread/CACHED variant (entities == null).

Common situations: Developers grab lazyList() for memory efficiency, then call subList() or loadRemaining() expecting List semantics; it fails because the lazy list never materializes entities into the backing array.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• No entity found for query
• Property '
• Expected unique result, but count was
• Cannot delete entity, key is null
• Entity does not exist in the database anymore

AI-assisted analysis of greenrobot/greenDAO@0bbb338e17 (2026-09-08). Data as JSON: /api/errors/118b1fce7c34fa51. Report an issue: GitHub.

Appendix: source

Thrown at DaoCore/src/main/java/org/greenrobot/greendao/query/LazyList.java:162

        if (size == 0) {
            cursor.close();
        }

        lock = new ReentrantLock();
    }

    /** Loads the remaining entities (if any) that were not loaded before. Applies to cached lazy lists only. */
    public void loadRemaining() {
        checkCached();
        int size = entities.size();
        for (int i = 0; i < size; i++) {
            get(i);
        }
    }

    protected void checkCached() {
        if (entities == null) {
            throw new DaoException("This operation only works with cached lazy lists");
        }
    }

    /** Like get but does not load the entity if it was not loaded before. */
    public E peek(int location) {
        if (entities != null) {
            return entities.get(location);
        } else {
            return null;
        }
    }

    @Override
    /** Closes the underlying cursor: do not try to get entities not loaded (using get) before. */
    public void close() {
        cursor.close();
    }

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