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Add jdbc-vs-jpa module: Spring Data JDBC vs JPA on a shared Order aggregate

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Same Customer/Order/OrderItem domain modelled with Hibernate/Spring Data JPA and
Spring Data JDBC side by side, both running through a shared StatementLoggingDataSource
so SQL-statement counts are directly comparable. 11 tests, 11 captured transcripts,
6 doc chapters. Companion repo for the ankurm.com article on when to drop the ORM.
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asmhatre
2026-09-17 19:09:35 +00:00
parent 585eed4d57
commit 448c383879
41 changed files with 1811 additions and 17 deletions
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jdbc-vs-jpa/docs/output/08-aggregate-reference-no-join.txt
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Scenario: load an order, then read its customer's id through the
AggregateReference — never call customerRepository.findById for it.
1. SELECT "JDBC_ORDER"."ID" AS "ID", "JDBC_ORDER"."VERSION" AS "VERSION", "JDBC_ORDER"."CUSTOMER_ID" AS "CUSTOMER_ID" FROM "JDBC_ORDER" WHERE "JDBC_ORDER"."ID" = ?
2. SELECT "JDBC_ORDER_ITEM"."ID" AS "ID", "JDBC_ORDER_ITEM"."SKU" AS "SKU", "JDBC_ORDER_ITEM"."QUANTITY" AS "QUANTITY", "JDBC_ORDER_ITEM"."ORDER_KEY" AS "ORDER_KEY" FROM "JDBC_ORDER_ITEM" WHERE "JDBC_ORDER_ITEM"."ORDER_ID" = ? ORDER BY "ORDER_KEY"
total statements: 2
statements touching jdbc_customer: 0
customer id obtained without a lookup: 3
AggregateReference<Customer, Long> is a typed foreign key: getId() is free
because the id is literally the column value already in hand from loading the
order. Nothing about Customer is fetched unless you explicitly ask a
CustomerRepository for it. This is the mechanism that keeps a multi-aggregate
object graph from becoming N+1 by default — there is no "default" traversal at
all across an aggregate boundary.