Add db-migrations-flyway-liquibase: Flyway vs Liquibase migrations, rollbacks and baselines on Spring Boot 4.1

Companion code for the Flyway vs Liquibase article: checksum validation, out-of-order
and repeatable migrations, baselining an existing schema, Flyway Community's undo/diff/deploy
stubs, concurrent-startup locking for both tools, Liquibase changeset identity and rollback
(auto-generated vs explicit), a verified Liquibase 5.0.3 filename-caching defect, the new
OSS license service, the FSL license change, and running both tools against one database.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Q6XdRjtsp4862EM44T7i9a

db-migrations-flyway-liquibase/src/test/java/com/ankurm/dbmigrations/BothTogetherTest.java

@@ -0,0 +1,99 @@
+package com.ankurm.dbmigrations;
+
+import java.nio.file.Path;
+import java.sql.Connection;
+
+import javax.sql.DataSource;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.flyway.autoconfigure.FlywayAutoConfiguration;
+import org.springframework.boot.jdbc.autoconfigure.DataSourceAutoConfiguration;
+import org.springframework.boot.liquibase.autoconfigure.LiquibaseAutoConfiguration;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Both starters, both enabled, one database — the question every "which one do I add" thread
+ * on Stack Overflow eventually asks in a comment. The naive answer is no: Boot wires Liquibase's
+ * {@code SpringLiquibase} bean before Flyway's {@code FlywayMigrationInitializer} in this
+ * configuration (an artifact of bean registration order here, not a documented contract), so by
+ * the time Flyway runs, Liquibase has already created tables, and Flyway's own safety check —
+ * "I found tables I don't recognize and no schema history table" — refuses to start. Turning on
+ * {@code baselineOnMigrate} alone is not enough here: its default {@code baselineVersion} (1)
+ * tells Flyway "pretend V1 already ran", which only makes sense if the existing schema really
+ * matches what V1 would have built. Liquibase's changelog built an unrelated {@code product}
+ * table, not {@code customer}, so V1 also has to be told to baseline-version 0 (nothing has run
+ * yet, from Flyway's point of view) so it runs its own migration set from scratch alongside
+ * whatever Liquibase already put there. See docs/14-running-both-at-once.md.
+ */
+class BothTogetherTest {
+
+    @Test
+    void enablingBothNaivelyFailsUntilFlywayIsToldToBaseline(@TempDir Path tmp) throws Exception {
+        Transcript t = Transcript.start("15-both-together-same-datasource",
+                "Flyway and Liquibase, both enabled: the naive failure, then the fix");
+
+        Path naiveDb = tmp.resolve("both-together-naive");
+        t.section("naive: both enabled, no other configuration");
+        new ApplicationContextRunner()
+                .withConfiguration(AutoConfigurations.of(DataSourceAutoConfiguration.class,
+                        FlywayAutoConfiguration.class, LiquibaseAutoConfiguration.class))
+                .withPropertyValues(
+                        "spring.datasource.url=jdbc:h2:file:" + naiveDb,
+                        "spring.datasource.username=sa",
+                        "spring.flyway.locations=classpath:db/migration",
+                        "spring.liquibase.change-log=classpath:db/changelog/db.changelog-master.yaml")
+                .run(ctx -> {
+                    assertThat(ctx).hasFailed();
+                    String message = rootMessage(ctx.getStartupFailure());
+                    t.line("context failed to start: " + message);
+                    assertThat(message).containsIgnoringCase("non-empty").containsIgnoringCase("baseline");
+                });
+
+        Path fixedDb = tmp.resolve("both-together-fixed");
+        t.section("fixed: spring.flyway.baseline-on-migrate=true, spring.flyway.baseline-version=0");
+        new ApplicationContextRunner()
+                .withConfiguration(AutoConfigurations.of(DataSourceAutoConfiguration.class,
+                        FlywayAutoConfiguration.class, LiquibaseAutoConfiguration.class))
+                .withPropertyValues(
+                        "spring.datasource.url=jdbc:h2:file:" + fixedDb,
+                        "spring.datasource.username=sa",
+                        "spring.flyway.locations=classpath:db/migration",
+                        "spring.flyway.baseline-on-migrate=true",
+                        "spring.flyway.baseline-version=0",
+                        "spring.liquibase.change-log=classpath:db/changelog/db.changelog-master.yaml")
+                .run(ctx -> {
+                    assertThat(ctx).hasNotFailed();
+                    DataSource ds = ctx.getBean(DataSource.class);
+                    try (Connection conn = ds.getConnection()) {
+                        t.line(DbDump.table(conn,
+                                "select table_name from information_schema.tables where table_schema='PUBLIC' order by table_name"));
+                        t.section("flyway_schema_history — baseline row at 0, then V1/V2 ran for real");
+                        String flywayHistory = DbDump.table(conn,
+                                "select \"version\", \"description\", \"type\", \"success\" from \"flyway_schema_history\" order by \"installed_rank\"");
+                        t.line(flywayHistory);
+                        t.section("databasechangelog — Liquibase's own bookkeeping, untouched by Flyway");
+                        t.line(DbDump.table(conn, "select id, author, exectype from databasechangelog order by orderexecuted"));
+
+                        String tables = DbDump.table(conn,
+                                "select table_name from information_schema.tables where table_schema='PUBLIC' order by table_name");
+                        assertThat(tables).contains("CUSTOMER").contains("PRODUCT").contains("DATABASECHANGELOG");
+                        assertThat(flywayHistory).contains("create customer").contains("seed customer");
+                    }
+                });
+
+        t.write();
+    }
+
+    private static String rootMessage(Throwable t) {
+        Throwable cause = t;
+        while (cause.getCause() != null) {
+            cause = cause.getCause();
+        }
+        return cause.getClass().getSimpleName() + ": " + cause.getMessage();
+    }
+}