How to ensure that there are no race conditions in a database update statement using spring

Question

Imagine there are two entities Children and Gifts . Let's say there are 1000 children and 10 gifts. Children will always try to grab available gifts, and gifts will be tagged to children on a "first come, first serve" basis.

Table structure

children table

+----+------+
| id | name |
+----+------+
|  1 | Sam  |
|  2 | John |
|  3 | Sara |
+----+------+

gift table

+----+---------+-------------+
| id |  gift   | children_id |
+----+---------+-------------+
|  1 | Toy Car |           2 |
|  2 | Doll    |           3 |
+----+---------+-------------+

Here the children_id is the child who grabbed the gift first.

In my application, I want to update the children_id in such a way that only the first child who initiated the request will get it and rest get a GiftUnavailableException .

How will I ensure that, even if a 1000 requests come at a time to grab a specific gift, only the first one will get it. Or how will I ensure that there are no race conditions for this update.

Are there any spring specific feature that I can make use of or are there any other ways.

I'm using spring-boot as my backend.

Answer 1

I can't post a comment so here I go !

I assume you are using Spring Data JPA.

Then you should use @Transactional annotation : This mean that everytime you are requesting your database, you do a transaction :

1. Begin Transaction
2. Execute Transaction
3. Commit Transaction

Lot of usefull informations about this (Read it !!): Spring @Transactional - isolation, propagation

You will need to seed your Transactional Isolation to Serializable and maybe change the propagation method.

And if you are not using Spring data JPA.. Well There is a synchronized keywords but I think it's a bit awful to use it here.