Moderate JPA Question 83 of 226

When do you use persist, merge, and Spring Data save?

Java Specialist · Speak this in 60–90 seconds · Faridabad & Delhi NCR

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Simple meaning

persist inserts a new entity and fails if the id already exists in some setups.

WHY — JPA instead of guessing?

Why interviewers care about JPA:

They are checking judgment

on JPA.

A good answer names

the situation, the default choice, and one exception - that reads as experience.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

STEPS — What happens step by step?

Before you speak the answer, walk the interviewer through these steps:

1
persist inserts a new
entity and fails if the id already exists in some setups.
2
merge copies state onto
a managed instance and is for detached updates.
3
Spring Data save inspects
whether the entity is new, then persist or merge, which can surprise you if you set ids manually.
4
Give an example
One tiny concrete case you can say aloud.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

Here's a short line you can speak, broken into clear beats:

Say this line

“merge copies state onto a managed instance and is for detached updates.”

Break into beats

mergecopiesstateontoamanaged

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Key takeaway

persist inserts a new entity and fails if the id already exists in some setups. merge copies state onto a managed instance and is for detached updates.