@ManyToOne relationship in Spring Boot - Performance & Optimization

Performance: @ManyToOne relationship

MEDIUM IMPACT

This affects database query performance and page load speed by controlling how related data is fetched and rendered.

Fetching related entities in a @ManyToOne relationship

Spring Boot

@ManyToOne(fetch = FetchType.LAZY)
private Category category;

Lazy fetching loads related data only when accessed, reducing initial load and speeding up first paint.

📈 Performance GainReduces initial query size and speeds up LCP by deferring related data loading.

Fetching related entities in a @ManyToOne relationship

Spring Boot

@ManyToOne(fetch = FetchType.EAGER)
private Category category;

Eager fetching loads related data immediately, increasing initial query size and slowing page load.

📉 Performance CostIncreases initial query time and data size, blocking rendering longer (worse LCP).

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
EAGER fetch in @ManyToOne	N/A (database query)	N/A	Blocks rendering longer due to data wait	[X] Bad
LAZY fetch in @ManyToOne	N/A (database query)	N/A	Faster initial render, data fetched on demand	[OK] Good

Rendering Pipeline

The @ManyToOne fetch strategy affects when related data is loaded from the database, impacting the time before the main content can be rendered.

→Data Fetching

→Rendering

→Interaction

⚠️ BottleneckData Fetching stage due to large or multiple queries triggered by eager loading.

Core Web Vital Affected

LCP

This affects database query performance and page load speed by controlling how related data is fetched and rendered.

Optimization Tips

1Use FetchType.LAZY in @ManyToOne to reduce initial data load and speed up page rendering.

2Avoid FetchType.EAGER unless you need related data immediately to prevent blocking rendering.

3Monitor backend query size and timing to optimize data fetching strategies.

Performance Quiz - 3 Questions

What is the main performance drawback of using FetchType.EAGER in a @ManyToOne relationship?

A It loads related data immediately, increasing initial load time.

B It delays loading related data until accessed, causing interaction lag.

C It reduces database query size, speeding up page load.

D It caches data on the client, increasing memory usage.

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and observe database API calls or backend requests triggered by entity fetching.

What to look for: Look for large or multiple data requests at page load indicating eager fetching; fewer or deferred requests indicate lazy fetching.