Flyway multiple metadata tables in one schema

问题:

I'm trying to use Flyway to version the database of a modular application. Each module has its own separate set of tables, and migration scripts that will control the versioning of that set of tables.

Flyway allows me to specify a different metadata table for each module - this way I can version each module independently. When I try to upgrade the application, I run a migration process for each module, each with its own table and set of scripts. Note that these tables are all in the same schema.

However, when I try to migrate my application, the first migration is the only one that works. Subsequent migrations fail with the following exception: org.flywaydb.core.api.FlywayException: Found non-empty schema(s) "public" without metadata table! Use baseline() or set baselineOnMigrate to true to initialize the metadata table.

If I create the metadata table for each module manually, migrations for each module work correctly. Creating the table myself rather than having Flyway create it for me seems like a hack to work around a problem, rather than a solution in itself.

Is this a valid way of managing multiple sets of tables independently, or is there a better way of doing this? Is it a valid approach to create the metadata table myself?

回答1:

An ideal solution for you would be to split your modules into schemas. This gives you an effective unit of isolation per module and is also a natural fit for modular applications (modules completely isolated and self managing), rather than dumping everything into a single schema (especially public). eg

application_database
    ├── public
    ├── module_1
    │   ├── schema_version
    │   ├── m1_t1
    │   └── m1_t2
    ├── module_2
    │   ├── schema_version
    │   ├── m2_t1
    │   └── m2_t2
    ...

Your second option is to remain using the public schema to host all tables, but use an individual schema for each schema_version. This is less refactoring effort but certainly a less elegant design than that mentioned above. eg

application_database
    ├── public
    │   ├── m1_t1
    │   ├── m1_t2
    │   ├── m2_t1
    │   └── m2_t2
    ├── module_1
    │   └── schema_version
    │
    ├── module_2
    │   └── schema_version
    ...

回答2:

I think you need to baseline each module before performing the migrate. You'll need to pass the table option to override schema_version for each module eg flyway.table=schema_version_module1. As the error message suggests you can also baselineOnMigrate however that is warned against in the docs (https://flywaydb.org/documentation/commandline/migrate).

We are considering a similar approach with another schema_version table to apply and log data fixes that cannot be rolled out to every environment cleanly.

回答3:

I have a similar situation, wherein I have two schemas (master & tenant), flyway works fine if those are separate MYSQL DB/SCHEMA, but for the case wherein I want both to be run against the same DB (which could be SQL Server, ORACLE). FLyway fails.

$ ./flyway migrate -table=schema_version -schemas=emm -locations=filesystem:sql/tenant
Flyway 4.2.0 by Boxfuse
Database: jdbc:mysql://localhost:3306/ (MySQL 5.6)
Creating schema `emm` ...
Creating Metadata table: `emm`.`schema_version`
Current version of schema `emm`: null
Migrating schema `emm` to version 1 - create umgmt user table
Successfully applied 1 migration to schema `emm` (execution time 00:00.162s).

$ ./flyway migrate -table=m_schema_version -schemas=emm -locations=filesystem:sql/master
Flyway 4.2.0 by Boxfuse
Database: jdbc:mysql://localhost:3306/ (MySQL 5.6)
Successfully validated 3 migrations (execution time 00:00.011s)
**ERROR: Found non-empty schema(s) `emm` without metadata table! Use baseline() or set baselineOnMigrate to true to initialize the metadata table.**