r2dbc: Spring Data R2DBC CRUD, DatabaseClient, reactive transactions and Testcontainers Postgres (post 2)

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b4VQVEJWetTT1dYzyJ

r2dbc/output/01-schema-init.txt

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+tables created by schema.sql: [account, customer, purchase_order]

r2dbc/output/02-crud.txt

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+save      -> id=1 name=Asha Rao
+findById  -> Customer[id=1, name=Asha Rao, [email protected], tier=GOLD]
+update    -> name=Asha Rao-Iyer (same id=1, SQL UPDATE)
+count     -> 1
+deleteById-> count now 0
+findById(9999) -> empty Mono (completes with no value, no exception)

r2dbc/output/03-lazy-pipeline.txt

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+built save(...) pipeline, never subscribed -> rows in table: 0
+after .block() on the same pipeline        -> rows in table: 1

r2dbc/output/04-queries.txt

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+findByTier(GOLD)        -> [Asha Rao, Meera Joshi]
+@Query searchByName(%RAO%) -> [Asha Rao]
+@Modifying changeTier    -> 1 row updated
+GOLD customers now       -> 3
+DatabaseClient totalSpent(ravi) -> 200.00

r2dbc/output/05-no-relations.txt

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+findAll() on Customer returns rows only. There is no orders field to be lazy or eager:
+  Customer[id=1, name=A, [email protected], tier=STANDARD]
+1+N queries (4 SQL statements for 3 customers) -> [A:2, B:1, C:0]
+two queries (2 SQL statements)                -> [A:2, B:1, C:0]
+one LEFT JOIN, grouped by hand (1 statement)   -> [A:2, B:1, C:0]
+all three strategies return identical aggregates: true

r2dbc/output/06-transactions.txt

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+NO transaction, failure after debit  -> alice=60.00 bob=50.00  (money vanished)
+@Transactional, failure after debit  -> alice=100.00 bob=50.00  (rolled back)
+TransactionalOperator, failure       -> alice=100.00 bob=50.00  (rolled back)
+TransactionalOperator, success       -> alice=60.00 bob=90.00  (committed)
+@Transactional, CHECK(balance>=0) violated on debit -> DataIntegrityViolationException; alice=100.00 bob=50.00
+transfer to a non-existent account   -> no error at all; alice=90.00 (debited, credit hit 0 rows)

r2dbc/output/07-throughput-indicative.txt

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+INDICATIVE, shared 2-vCPU sandbox, database in a container on the same host.
+4000 x 'SELECT ... WHERE id = ?' per round, 100 in flight, pool size 20, 5 rounds after 1 warm-up each.
+queries/second, sorted:
+  R2DBC DatabaseClient      : [233, 288, 361, 427, 435]  median=361
+  JDBC + virtual threads    : [1240, 1281, 1348, 1558, 3084]  median=1348

r2dbc/output/08-missing-testcontainers-r2dbc.txt

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+mvn test with testcontainers-r2dbc removed from the pom:
+Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 57.47 s <<< FAILURE! -- in com.ankurm.r2dbc.R2dbcDemoTest
+Failed to instantiate [io.r2dbc.pool.ConnectionPool]: Factory method 'connectionFactory' threw exception with message: org/testcontainers/r2dbc/R2DBCDatabaseContainer
+Caused by: java.lang.ClassNotFoundException: org.testcontainers.r2dbc.R2DBCDatabaseContainer