Java.Hibernate.Medium.How can you cache query results?

✅ Short Answer

You can cache query results in Hibernate by:
1️⃣ Enabling the query cache in your Hibernate configuration.
2️⃣ Marking individual queries as cacheable with .setCacheable(true).
This allows Hibernate to store entire result sets in the second-level cache, speeding up repeated queries.

🔎 Detailed Explanation

🔹 1) Enable the Query Cache Globally
In your Hibernate config (e.g., hibernate.cfg.xml or application.properties):

hibernate.cache.use_query_cache=true

✅ Note: Query cache depends on second-level cache → it won’t work without it.

🔹 2) Mark Specific Queries as Cacheable
When building your query, call:

Query<MyEntity> query = session.createQuery("FROM MyEntity WHERE status = :status", MyEntity.class);
query.setParameter("status", "ACTIVE");
query.setCacheable(true); // enables caching of this query's result set
List<MyEntity> results = query.getResultList();

✅ Hibernate caches the list of entity IDs matching the query + the entities themselves in the second-level cache.

🔹 3) (Optional) Set Cache Region
You can group cached queries in regions with different settings:

query.setCacheRegion("myQueryCacheRegion");

🔹 4) Important Behavior

• If you update any entity in the result set, Hibernate invalidates the cached query → ensures consistency.
• Query cache does not cache individual entities — it only caches the query result (IDs) → entities themselves must be second-level cache-enabled.

🧑‍💻 Practical Example

List<Product> products = session.createQuery(
    "FROM Product p WHERE p.category = :category", Product.class)
  .setParameter("category", "Books")
  .setCacheable(true)
  .getResultList();

📊 Benefits of Query Cache

✅ Useful for expensive, frequently repeated queries (e.g., top 10 products, homepage listings).
✅ Reduces DB load when the same result set is requested often.

⚠️ Pitfalls

❌ Not helpful for highly dynamic queries → too many cache entries → bloated cache.
❌ Query cache must be combined with second-level entity caching → otherwise it can’t serve objects efficiently.

📌 Key Takeaways

✅ To cache query results:

• Enable hibernate.cache.use_query_cache.
• Call .setCacheable(true) on your query.
  ✅ The query cache speeds up repeated queries by storing result sets, not entities themselves.
  ✅ Always ensure entity second-level caching is configured → query cache works hand-in-hand with it.