A PostgreSQL specific migration tool
Project description
Tusker
A PostgreSQL specific migration tool
Elevator pitch
Do you want to write your database schema directly as SQL which is understood by PostgreSQL?
Do you want to be able to make changes to this schema and generate the SQL which is required to migrate between the old and new schema version?
Tusker does exactly this.
Installation
pipx install tusker
Now you should be able to run tusker. Give it a try:
tusker --help
Getting started
Once tusker is installed create a new file called schema.sql
:
CREATE TABLE fruit (
id BIGINT GENERATED BY DEFAULT AS IDENTITY,
name TEXT NOT NULL UNIQUE
);
You probably want to create an empty migrations
directory, too:
mkdir migrations
Now you should be able to create your first migration:
tusker diff
The migration is printed to the console and all you need to do is
copy and paste the output into a new file in the migrations directory.
Alternatively you can also pipe the output of tusker diff
into the
target file:
tusker diff > migrations/0001_initial.sql
After that check that your schema.sql
and your migrations
are in sync:
tusker diff
This should give you an empty output. This means that there is no difference between applying the migrations in order and the target schema.
Alternatively you can run the check command:
tusker check
If you want to change the schema in the future simply change the schema.sql
and run tusker diff
to create the migration for you.
Give it a try and change the schema.sql
:
CREATE TABLE fruit (
id BIGINT GENERATED BY DEFAULT AS IDENTITY,
name TEXT NOT NULL UNIQUE,
color TEXT NOT NULL DEFAULT ''
);
Create a new migration:
tusker diff > migrations/0002_fruit_color.sql
Congratulations! You are now using SQL to write your migrations. You are no longer limited by a 3rd party data definition language or an object relational wrapper.
Configuration
In order to run tusker you do not need a configuration file. The following defaults are assumed:
- The file containing your database schema is called
schema.sql
- The directory containing the migrations is called
migrations
- Your current user can connect to the database using a unix domain socket without a password.
You can also create a configuration file called tusker.toml
. The default
configuration looks like that:
[schema]
filename = "schema.sql"
[migrations]
filename = "migrations/*.sql"
[database]
#host = ""
#port = 5432
#user = ""
#password = ""
dbname = "tusker"
[migra]
safe = false
privileges = false
Instead of the exploded form of host
, port
, etc. it
is also possible to pass a connection URL:
[schema]
filename = "schema.sql"
[migrations]
filename = "migrations/*.sql"
[database]
url = "postgresql:///my_awesome_db"
You can also use an environment variable in place of a hard-coded value:
[database]
url = "${DATABASE_URL}"
How can I use the generated SQL files?
The resulting SQL files can either be applied to the database by hand or by using one of the many great tools and libraries which support applying SQL files in order.
Some recommendations are:
How does it work?
Upon startup tusker
reads all files from the migrations
directory
and runs them on an empty database. Another empty database is created
and the target schema is created. Then those two schemas are
diffed using the excellent migra
tool and the output printed to the console.
Tusker is unsafe
by default
Unlike migra
the tusker
command by default does not throw an
exception when a drop
-statement is generated. Always check your
generated migrations prior to running them. If you want the same
behavior as migra you can either use the --safe
argument or set
the migra.safe
configuration option to True
in your tusker.toml
file.
FAQ
Is it possible to split the schema into multiple files?
Yes. This feature has been added in 0.3. You can now use glob
patterns as
part of the schema.filename
setting. e.g.:
[schema]
filename = "schema/*.sql"
As of 0.4.5 recursive glob patterns are supported as well:
[schema]
filename = "schema/**/*.sql"
Is it possible to diff the schema and/or migrations against an existing database?
Yes. This feature has been added in 0.2. You can pass a from
and to
argument to the tusker diff
command. Check the output of tusker diff --help
for
more details.
Tusker printed an error and left the temporary databases behind. How can I remove them?
Run tusker clean
. This will remove all databases which were created
by previous runs of tusker. Tusker only removes databases which are
marked with a CREATED BY TUSKER
comment.
What does the dbname
setting in tusker.toml
mean?
When diffing against a ready migrated database this database name is used. This command will print out the difference between the current database schema and the target schema:
tusker diff database
Tusker also needs to create temporary databases when diffing against the schema
and/or migrations
. The two databases are called {dbname}_{timestamp}_schema
and {dbname}_{timestamp}_migrations
.
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