Hibernate findById或SQL查询

Question

I have many time scenarios that I only want to access only one/two/ or some no of columns and we are using hibernate so I want to know which is better for performance either

1) by fetching findById method of hibernate, which is very convenient for me because I have to just call it, but I think it will be not good in performance because it will fetch all column rather I require only some.

2) Or by creating my query each time that is tedious but it will be better in performance

So I want suggestion regarding what should I use?

Answer 1

To answer more specifically, it would be helpful if you included a code snippet. In general though, findById is a convenience method that will result in a query very similar to what you would write yourself. So writing the query yourself and returning only the columns you need (constructor expressions are useful) would be better in terms of performance. The question I would ask is, is that improved performance worth the more complicated code? You can always optimize your queries later.

Answer 2

It entirely depends on the entity which is being loaded. If the entity is one, with lots of relationships, and all you need is a couple of fields in the root entity, it is definitely worth writing your own query as Hibernate generates queries with JOIN s to load the entity which can be very expensive. The other thing to consider here is that, you can always handle the fields that are being loaded using LAZY or EAGER loading but these settings are static and will be applied permanently to your entity.
On the other hand if the entity doesn't have many relationships, I believe the most expensive part is the conversation time between DB and your application, thus loading a number of extra fields can be ignored.