To get a bulk insert with Spring Boot and Spring Data JPA you need only two things:
set the option spring.jpa.properties.hibernate.jdbc.batch_size to appropriate value you need (for example: 20).
use saveAll() method of your repo with the list of entities prepared for inserting.
Working example is here.
Regarding the transformation of the insert statement into something like this:
INSERT INTO table VALUES (1, 2), (3, 4), (5, 6)
the such is available in PostgreSQL: you can set the option reWriteBatchedInserts to true in jdbc connection string:
jdbc:postgresql://localhost:5432/db?reWriteBatchedInserts=true
then jdbc driver will do this transformation.
Additional info about batching you can find here.
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Demo project in Kotlin: sb-kotlin-batch-insert-demo
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