Dbmate is a database migration tool, to keep your database schema in sync across multiple developers and your production servers.
It is a standalone command line tool, which can be used with Go, Node.js, Python, Ruby, PHP, or any other language or framework you are using to write database-backed applications. This is especially helpful if you are writing many services in different languages, and want to maintain some sanity with consistent development tools.
For a comparison between dbmate and other popular database schema migration tools, please see the [Alternatives](#alternatives) table.
Dbmate locates your database using the `DATABASE_URL` environment variable by default. If you are writing a [twelve-factor app](http://12factor.net/), you should be storing all connection strings in environment variables.
To make this easy in development, dbmate looks for a `.env` file in the current directory, and treats any variables listed there as if they were specified in the current environment (existing environment variables take preference, however).
If you do not already have a `.env` file, create one and add your database connection URL:
When connecting to Postgres, you may need to add the `sslmode=disable` option to your connection string, as dbmate by default requires a TLS connection (some other frameworks/languages allow unencrypted connections by default).
SQLite databases are stored on the filesystem, so you do not need to specify a host. By default, files are relative to the current directory. For example, the following will create a database at `./db/database_name.sqlite3`:
```sh
DATABASE_URL="sqlite:///db/database_name.sqlite3"
```
To specify an absolute path, add an additional forward slash to the path. The following will create a database at `/tmp/database_name.sqlite3`:
To create a new migration, run `dbmate new create_users_table`. You can name the migration anything you like. This will create a file `db/migrations/20151127184807_create_users_table.sql` in the current directory:
```sql
-- migrate:up
-- migrate:down
```
To write a migration, simply add your SQL to the `migrate:up` section:
> Note: Migration files are named in the format `[version]_[description].sql`. Only the version (defined as all leading numeric characters in the file name) is recorded in the database, so you can safely rename a migration file without having any effect on its current application state.
> Note: `dbmate up` will create the database if it does not already exist (assuming the current user has permission to create databases). If you want to run migrations without creating the database, run `dbmate migrate`.
By default, dbmate doesn't know how to roll back a migration. In development, it's often useful to be able to revert your database to a previous state. To accomplish this, implement the `migrate:down` section:
dbmate supports options passed to a migration block in the form of `key:value` pairs. List of supported options:
*`transaction`
#### transaction
`transaction` is useful if you need to run some SQL which cannot be executed from within a transaction. For example, in Postgres, you would need to disable transactions for migrations that alter an enum type to add a value:
```sql
-- migrate:up transaction:false
ALTER TYPE colors ADD VALUE 'orange' AFTER 'red';
ALTER TYPE colors ADD VALUE 'yellow' AFTER 'orange';
```
`transaction` will default to `true` for if your database supports it.
When you run the `up`, `migrate`, or `rollback` commands, dbmate will automatically create a `./db/schema.sql` file containing a complete representation of your database schema. Dbmate keeps this file up to date for you, so you should not manually edit it.
It is recommended to check this file into source control, so that you can easily review changes to the schema in commits or pull requests. It's also possible to use this file when you want to quickly load a database schema, without running each migration sequentially (for example in your test harness). However, if you do not wish to save this file, you could add it to `.gitignore`, or pass the `--no-dump-schema` command line option.
To dump the `schema.sql` file without performing any other actions, run `dbmate dump`. Unlike other dbmate actions, this command relies on the respective `pg_dump`, `mysqldump`, or `sqlite3` commands being available in your PATH. If these tools are not available, dbmate will silenty skip the schema dump step during `up`, `migrate`, or `rollback` actions. You can diagnose the issue by running `dbmate dump` and looking at the output:
```sh
$ dbmate dump
exec: "pg_dump": executable file not found in $PATH
```
On Ubuntu or Debian systems, you can fix this by installing `postgresql-client`, `mysql-client`, or `sqlite3` respectively. Ensure that the package version you install is greater than or equal to the version running on your database server.
> Note: The `schema.sql` file will contain a complete schema for your database, even if some tables or columns were created outside of dbmate migrations.
If you use a Docker development environment for your project, you may encounter issues with the database not being immediately ready when running migrations or unit tests. This can be due to the database server having only just started.
In general, your application should be resilient to not having a working database connection on startup. However, for the purpose of running migrations or unit tests, this is not practical. The `wait` command avoids this situation by allowing you to pause a script or other application until the database is available. Dbmate will attempt a connection to the database server every second, up to a maximum of 60 seconds.
If the database is available, `wait` will return no output:
```sh
$ dbmate wait
```
If the database is unavailable, `wait` will block until the database becomes available:
```sh
$ dbmate wait
Waiting for database....
```
You can chain `wait` together with other commands if you sometimes see failures caused by the database not yet being ready:
```sh
$ dbmate wait && dbmate up
Waiting for database....
Creating: myapp_development
```
If the database is still not available after 60 seconds, the command will return an error:
```sh
$ dbmate wait
Waiting for database............................................................
Error: unable to connect to database: pq: role "foobar" does not exist
```
Please note that the `wait` command does not verify whether your specified database exists, only that the server is available and ready (so it will return success if the database server is available, but your database has not yet been created).
The following command line options are available with all commands. You must use command line arguments in the order `dbmate [global options] command [command options]`.
*`--env, -e "DATABASE_URL"` - specify an environment variable to read the database connection URL from.
For example, before running your test suite, you may wish to drop and recreate the test database. One easy way to do this is to store your test database connection URL in the `TEST_DATABASE_URL` environment variable:
Alpine linux uses [musl libc](https://www.musl-libc.org/), which is incompatible with how we build SQLite support (using [cgo](https://golang.org/cmd/cgo/)). If you want Alpine linux support, and don't mind sacrificing SQLite support, please use the `dbmate-linux-musl-amd64` build found on the [releases page](https://github.com/amacneil/dbmate/releases).
Why another database schema migration tool? Dbmate was inspired by many other tools, primarily [Active Record Migrations](http://guides.rubyonrails.org/active_record_migrations.html), with the goals of being trivial to configure, and language & framework independent. Here is a comparison between dbmate and other popular migration tools.
> :eight_pointed_black_star: In theory these tools could be used with other languages, but a Go development environment is required because binary builds are not provided.
*If you notice any inaccuracies in this table, please [propose a change](https://github.com/amacneil/dbmate/edit/master/README.md).*
