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Clarify datasource initializer scope

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This commit clarifies the scope of the datasource initializr. In
particular, it is not possible to create the schema with that facility
and let Hibernate creates additional tables.

Closes gh-9048
This commit is contained in:
Stephane Nicoll 2017-10-03 15:23:58 +02:00
parent 71c15cb65e
commit 7e08e47b75
1 changed files with 16 additions and 22 deletions
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38
spring-boot-docs/src/main/asciidoc/howto.adoc
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@ -2136,30 +2136,24 @@ is a Hibernate feature (nothing to do with Spring).
[[howto-initialize-a-database-using-spring-jdbc]]
=== Initialize a database using Spring JDBC
Spring JDBC has a `DataSource` initializer feature. Spring Boot enables it by default and
loads SQL from the standard locations `schema.sql` and `data.sql` (in the root of the
classpath). In addition Spring Boot will load the `schema-${platform}.sql`
and `data-${platform}.sql` files (if present), where
`platform` is the value of `spring.datasource.platform`, e.g. you might choose to set
it to the vendor name of the database (`hsqldb`, `h2`, `oracle`, `mysql`,
`postgresql` etc.). Spring Boot enables the fail-fast feature of the Spring JDBC
initializer by default, so if the scripts cause exceptions the application will fail
to start. The script locations can be changed by setting `spring.datasource.schema` and
`spring.datasource.data`, and neither location will be processed if
`spring.datasource.initialize=false`.
=== Initialize a database
Spring Boot can automatically create the schema (DDL scripts) of your `DataSource` and
initialize it (DML scripts): it loads SQL from the standard root classpath locations
`schema.sql` and `data.sql`, respectively. In addition Spring Boot will process the
`schema-${platform}.sql` and `data-${platform}.sql` files (if present), where `platform`
is the value of `spring.datasource.platform`. This allows you to switch to database
specific scripts if necessary, e.g. you might choose to set it to the vendor name of the
database (`hsqldb`, `h2`, `oracle`, `mysql`, `postgresql` etc.).
To disable the fail-fast you can set `spring.datasource.continue-on-error=true`. This can be
useful once an application has matured and been deployed a few times, since the scripts
can act as '`poor man's migrations`' -- inserts that fail mean that the data is already
there, so there would be no need to prevent the application from running, for instance.
Spring Boot enables the fail-fast feature of the Spring JDBC initializer by default, so if
the scripts cause exceptions the application will fail to start. You can tune that using
`spring.datasource.continue-on-error`.
If you want to use the `schema.sql` initialization in a JPA app (with
Hibernate) then `ddl-auto=create-drop` will lead to errors if
Hibernate tries to create the same tables. To avoid those errors set
`ddl-auto` explicitly to "" (preferable) or "none". Whether or not you use
`ddl-auto=create-drop` you can always use `data.sql` to initialize new
data.
NOTE: In a JPA-based app, you can choose to let Hibernate create the schema or use
`schema.sql` but not both. Make sure to disable `spring.jpa.hibernate.ddl-auto` if you
chose the later.
You can also disable initialization by setting `spring.datasource.initialize` to `false`.