Скачать или смотреть Understanding Eager vs Lazy Fetching in @ Ref Annotation of Spring Data for ArangoDB

Discover whether the `@ Ref` annotation in ArangoDB's Spring Data uses eager or lazy fetching for referenced objects, and learn how to control this behavior effectively.
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Understanding Eager vs Lazy Fetching in @ Ref Annotation of Spring Data for ArangoDB

When working on a schema involving referenced objects in ArangoDB using Spring Data, a common question that arises is: How are these referenced objects fetched—are they fetched eagerly or lazily? This distinction is crucial as it impacts performance and data retrieval strategies in your applications.

What is Eager and Lazy Fetching?

Before delving into the specifics of the @ Ref annotation, it’s important to understand the concepts of eager and lazy fetching:

Eager Fetching: In this approach, the referenced objects are fetched immediately along with the main entity. This can simplify access to related objects but may increase the amount of data loaded, leading to potentially slower performance, especially if the referenced objects are large or numerous.

Lazy Fetching: This method defers the loading of the referenced objects until they are specifically requested. This can result in better initial load performance, but it may lead to additional database hits when accessing those referenced objects later.

Default Behavior of the @ Ref Annotation

In the context of the @ Ref annotation in ArangoDB's Spring Data (specifically version 3.2.5), the default fetching strategy is eager. This means that when you retrieve an entity that references other documents, those documents are also fetched at the same time.

Dissecting the @ Ref Annotation

The key details of the @ Ref annotation can be found in its implementation:

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RetentionPolicy.RUNTIME: This indicates that the annotation is retained at runtime, allowing for reflection-based operations.

ElementType.FIELD: This specifies that the annotation can be applied to fields.

lazy() method: This boolean method indicates whether the entity should be loaded lazily. By default, it is set to false, enforcing the eager fetching strategy.

Enabling Lazy Fetching

If your application requires the referenced objects to be loaded lazily instead of eagerly, you can easily achieve this by setting the lazy attribute in the @ Ref annotation. Here’s how to do it:

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By annotating your field with @ Ref(lazy = true), you instruct the framework to load that entity's referenced documents lazily, ensuring that they are only fetched when explicitly accessed.

Conclusion

Understanding how the @ Ref annotation behaves in terms of fetching strategies is vital for building efficient data access layer in your applications. By default, as of version 3.2.5, the fetching is eager, but you have the flexibility to control this behavior by setting the lazy parameter to true whenever necessary.

When designing your schema and considering performance, carefully choose between eager and lazy fetching to optimize your application's data retrieval capabilities.