Spring Boot 'Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured': how do I fix it?

Cause: Spring Boot saw a JDBC or JPA starter (so it needs a DataSource) but found no spring.datasource.url and no embedded database (H2, HSQL or Derby) on the classpath to fall back to. Common triggers: the property is missing or in the wrong profile or file, the properties file is not on the classpath or has the wrong name, the application is picking up a different profile, or a starter was added to a module that does not actually use a database. Fix (best first): 1. Set the connection in application.properties or application.yaml: spring.datasource.url (a jdbc: URL), spring.datasource.username and spring.datasource.password. The driver class is normally deduced from the URL; set spring.datasource.driver-class-name only if needed, and make sure the JDBC driver jar is a dependency. 2. Check the file is actually used: correct name and location (src/main/resources), and the active profile (spring.profiles.active) matches an application-<profile> file that defines the URL. Keep real passwords in environment variables or a secrets store, not in the repository. 3. If you want an in-memory database for development or tests, add the embedded database dependency (for example H2) and remove the explicit URL; Boot configures it without a URL. If several embedded databases are present, set spring.datasource.embedded-database-connection. 4. If this module should not use a database, remove the JDBC/JPA starter, or exclude DataSourceAutoConfiguration on the application class. 5. If you define your own DataSource bean, auto-configuration backs off; with HikariDataSource used directly the property name is jdbc-url, or use a DataSourceProperties bean so url works. Verify: The application starts, the log shows the pool (HikariPool by default) starting, and a simple repository or JdbcTemplate query succeeds. Sources: https://docs.spring.io/spring-boot/reference/data/sql.html https://docs.spring.io/spring-boot/how-to/data-access.html