What is eager loading in hibernate

This is because by default fetch strategy for all oneToMany or any other relation is lazy call to DB on demand and when you have closed the session, you have no power to communicate with database. Lazy Loading vs Eager Loading Fetching or loading data can be primarily classified into two types: eager and lazy. Eager Loading And Lazy Loading The first thing that we should discuss here is what lazy loading and eager loading are: Eager Loading is a design pattern in which data initialization occurs on the spot.

It means that collections are fetched fully at the time their parent is fetched fetch immediately Lazy Loading is a design pattern which is used to defer initialization of an object until the point at which it is needed. Solution for this is to use: Open Session in View - In which you keep the session open even on the rendered view.

Previous Next. This website is not affiliated with Stack Overflow. It means that collections are fetched fully at the time their parent is fetched fetch immediately. Lazy Loading is a design pattern which is used to defer initialization of an object until the point at which it is needed. This can effectively contribute to application's performance. Look at the Set of orderDetail that we have. Now let's have a look at the OrderDetail class :. Okay, so we talked about the fact that FetchType. LAZY is the default fetch type for all Hibernate annotation relationships.

We also talked about the fact that when you use the Lazy fetch type, Hibernate won't load the relationships for that particular object instance. So then, what's the difference between Eager and Lazy? Fetch type Eager is essentially the opposite of Lazy, Eager will by default load ALL of the relationships related to a particular object loaded by Hibernate. This means that if you change the relationship to be this:.

Hibernate will now load the user profile into the user object by default. This means that if you access user. If using the lazy loading approach can cause NullPointerException s, then why the heck would you want to use it? Well, let's just take a minute to think about this. Let's assume we had a User object that has 10 different relationships to other objects.

Let's also say that you have a user that's trying to login and you just want to check to see if their username and password is correct and matches what's stored in the database. Think of the cascading massacre of objects loaded from the database into memory! So having outlined the differences between these two approaches, I hope you realize that Lazy loading is a suggested route to take your application code in most scenarios.

So having said that, how do we make use of Lazy loading with a Spring enabled application? The code that you don't see is the transactional code enabled by the Transactional annotation in your DAOs and this is something that you always need to keep in mind when using Lazy loading. Having said that, let's take a look at an example of Lazy loading using our User object. Let's assume we have our User object which has a Lazy load fetch enabled to the Profile object.