Hi everyone,
We are back again with a new release of Atlas, v0.24. In this release
we double down on the core principle that has been guiding us from the start: enabling developers to manage their
database schema as code. The features we announce today may appear like a yet another cool addition to Atlas, but
I am fairly confident, that in a few years' time, they will be recognized as something foundational.
In this release we introduce:
schema test - a new command (and framework) for testing your database schema using familiar software testing
paradigms.migrate test - a new command for testing writing tests for you schema migrations.- Enhanced editor support - we have added support for some long awaited features in our VSCode and JetBrains plugins:
multi-file schemas, jump to definition, and support for much larger schemas.
Doubling Down on Database Schema-as-Code
The core idea behind Atlas is to enable developers to manage their Database Schema-as-Code. Before we jump into the
recent additions to Atlas, I would like to take a moment to reflect on why our industry seems to think that "X-as-Code"
is a great idea.
In a nutshell, the "X-as-Code" movement is about being able to describe the desired state of a system (whether it's
infrastructure, configuration, or schema) in a declarative way and then have that state enforced by a tool.
So why is having things described as code so great? Here are a few reasons:
- Code can be versioned. This means that you can track changes to your system over time, easily compare states,
and rollback as needed.
- Code is understood by machines. As formal languages, code can be parsed, analyzed, and executed by machines.
- Code can be tested and validated. By using software testing paradigms, you can ensure that your system behaves as
expected in an automated way.
- Code can be shared and reused. Code allows us to transfer successful ideas and implementations between projects
and teams.
- Code has a vast ecosystem of productivity tools. By using code, you can leverage the vast ecosystem of tools and
practices that have been developed by software engineers over the years.
Our core goal with Atlas is to bring these benefits to the world of database schema management. We believe that by
enabling developers to manage their database schema as code, we can help them build better, more reliable systems.
Today we bring one of the most important tenets of modern software development to the world of database schema management:
testing.
Why test your database schema and migrations?
Testing is a fundamental part of modern software development. By writing tests, you can ensure that your code behaves
as expected, catch bugs early, and prevent regressions.
When it comes to database schemas, testing is just as important. Databases are much more than just a
storage layer, they can be programmed, enforce logic and constraints, and have complex relationships between tables.
For example, table triggers allow you to run custom code when certain events occur, and you should be able to test
that this code behaves as expected and that later changes to the schema do not break it. In a similar vein, developers
can provide complex expressions in check constraints that should be tested to ensure they are working as expected.
When it comes to migrations, testing is equally important. Atlas already provides the migrate lint command to help you catch
invalid migrations and common mistakes. However, migrate test takes validating your migrations a step further.
Many teams use migrations as a mechanism to apply data migrations in tandem with schema changes. As they involve data,
these changes are super risky, yet it is notoriously hard to test them. By providing a way to test your migrations,
we hope to make this process easier and more reliable.
Introducing schema test
The schema test command allows you to write tests for your database schema using familiar software testing paradigms.
To get started, first install the latest version of the Atlas CLI:
- macOS + Linux
- Homebrew
- Docker
- Windows
- Manual Installation
To download and install the latest release of the Atlas CLI, simply run the following in your terminal:
curl -sSf https://atlasgo.sh | sh
Get the latest release with Homebrew:
brew install ariga/tap/atlas
To pull the Atlas image and run it as a Docker container:
docker pull arigaio/atlas
docker run --rm arigaio/atlas --help
If the container needs access to the host network or a local directory, use the --net=host flag and mount the desired
directory:
docker run --rm --net=host \
-v $(pwd)/migrations:/migrations \
arigaio/atlas migrate apply
--url "mysql://root:pass@:3306/test"
Download the latest release and
move the atlas binary to a file location on your system PATH.
If you want to manually install the Atlas CLI, pick one of the below builds suitable for your system.
Next, login to your Atlas account to activate the new schema testing features:
Let's see a brief example. We will begin our project by defining a basic Atlas project file named atlas.hcl:
atlas.hcl
env "local" {
src = "file://schema.hcl"
dev = "docker://postgres/16/dev?search_path=public"
}
atlas.hcl
env "local" {
src = "file://schema.sql"
dev = "docker://postgres/16/dev?search_path=public"
}
Next, let's define a PostgreSQL Domain
to model a data type for a us_postal_code:
schema.hcl
schema "public" {
}
domain "us_postal_code" {
schema = schema.public
type = text
check {
expr = "VALUE ~ '^\d{5}$' OR VALUE ~ '^\d{5}-\d{4}$'"
}
}
schema.sql
CREATE DOMAIN "us_postal_code" AS text
CONSTRAINT "us_postal_code_check"
CHECK (
(VALUE ~ '^\d{5}$'::text) OR
(VALUE ~ '^\d{5}-\d{4}$'::text)
);
Next, let's create a file named "schema.test.hcl" with the following content:
schema.test.hcl
test "schema" "postal" {
exec {
sql = "select 'hello'::us_postal_code"
}
}
Per testing best practices, we start with a test that is going to fail, since the string "hello" is not a valid US postal code.
Now, we can run the test using the schema test command:
atlas schema test --env local
The output will be:
-- FAIL: postal (319µs)
schema.test.hcl:2:
Error: pq: value for domain us_postal_code violates check constraint "us_postal_code_check"
FAIL
As expected, the test failed, and we can now fix the test by catching that error and verifying its message:
schema.test.hcl
test "schema" "postal" {
catch {
sql = "select 'hello'::us_postal_code"
error = "value for domain us_postal_code violates check constraint"
}
}
Re-running the test:
atlas schema test --env local
The output will be:
-- PASS: postal (565µs)
PASS
Now we can expand the test to cover more cases, such as valid postal codes and more invalid cases:
schema.test.hcl
test "schema" "postal" {
exec {
sql = "select '12345'::us_postal_code"
output = "12345"
}
exec {
sql = "select '12345-1234'::us_postal_code"
output = "12345-1234"
}
catch {
sql = "select 'hello'::us_postal_code"
error = "value for domain us_postal_code violates check constraint"
}
catch {
sql = "select '1234'::us_postal_code"
error = "value for domain us_postal_code violates check constraint"
}
assert {
sql = "select '12345'::us_postal_code::text='12345'"
}
log {
message = "Hooray, testing!"
}
}
Re-running the test:
atlas schema test --env local
The output will be:
-- PASS: postal (1ms)
schema.test.hcl:21: Hooray, testing!
PASS
Let's review what happens when we run atlas schema test:
- Atlas will apply the schema for the
local environment on the dev database.
- Atlas will search the current directory for files matching the pattern
*.test.hcl.
- For each test file found, Atlas will execute a test for each
test "schema" "<name>" block.
- Here are the possible test blocks:
exec - Executes a SQL statement and verifies the output.catch - Executes a SQL statement and verifies that an error is thrown.assert - Executes a SQL statement and verifies that the output is true.log - Logs a message to the test output.
Using this modest framework, you can now write tests for your database schema, ensuring that it behaves as expected.
This command can be integrated into your local development workflow or even as part of your CI pipeline further
ensuring the quality of your database schema changes.
Introducing migrate test
The migrate test command allows you to write tests for your schema migrations. This is a powerful feature that
enables you to test logic in your migrations in a minimal and straightforward way. The command is similar to schema test
but is focused on testing migrations.
Suppose we are refactoring an existing table users which has a name column that we want to split into
first_name and last_name columns. The recommended way to do this kind of refactoring in a backward-compatible
way. Initially, we will be adding the new columns In Atlas DDL, the schema change would look roughly like this:
schema.hcl
table "users " {
// .. redacted
+ column "first_name" {
+ type = text
+ null = true
+ }
+ column "last_name" {
+ type = text
+ null = true
+ }
}
Next, we will use Atlas to generate a migration for this change:
atlas migrate diff --env local
A new file will be created in our migrations directory:
20240613061102.sql
ALTER TABLE "users" ADD COLUMN "first_name" text NULL, ADD COLUMN "last_name" text NULL;
Next, let's add the backfill logic to populate the new columns with the data from the name column:
20240613061102.sql
ALTER TABLE "users" ADD COLUMN "first_name" text NOT NULL, ADD COLUMN "last_name" text NOT NULL;
UPDATE "users" SET "first_name" = split_part("name", ' ', 1), "last_name" = split_part("name", ' ', 2);
After changing the contents of our migration file, we must update our atlas.sum file to reflect the changes:
atlas migrate hash --env local
Next, we will create a test case to verify that our migration works correctly in different cases. Let's add the
following block to a new file named migrations.test.hcl:
migrations.test.hcl
test "migrate" "name_split" {
migrate {
to = "20240613061046"
}
exec {
sql = "insert into users (name) values ('Ada Lovelace')"
}
migrate {
to = "20240613061102"
}
exec {
sql = "select first_name,last_name from users"
output = "Ada, Lovelace"
}
}
Let's explain what this test does:
- We start by defining a new test case named
name_split.
- The
migrate block runs migrations up to a specific version. In this case, we are running all migrations up to the
version before the one we just added.
- The
exec block runs a SQL statement. In this case, we are inserting a new user with the name "Ada Lovelace".
- Next, we run our new migration,
20240613061102.
- Finally, we run a SQL statement to verify that the
first_name and last_name columns were populated correctly.
Let's run the test:
atlas migrate test --env local
The output will be:
-- PASS: name_split (33ms)
PASS
Great, our test passed! We can now be confident that our migration works as expected.
Testing Edge Cases
With our test infra all set up, it's now easy to add more test cases to cover edge cases. For example, we can add a test
to verify that our splitting logic works correctly for names that include a middle name, for example, John Fitzgerald Kennedy:
migrations.test.hcl
test "migrate" "name_split_middle_name" {
migrate {
to = "20240613061046"
}
exec {
sql = "insert into users (name) values ('John Fitzgerald Kennedy')"
}
migrate {
to = "20240613061102"
}
exec {
sql = "select first_name,last_name from users"
output = "John Fitzgerald, Kennedy"
}
}
We expect to see only the family name in the last_name column, and the rest of the name in the first_name column.
Will it work? Let's run the test:
atlas migrate test --env local --run name_split_middle_name
Our test fails:
-- FAIL: name_split_middle_name (32ms)
migrations.test.hcl:27:
Error: no match for `John Fitzgerald, Kennedy` found in "John, Fitzgerald"
FAIL
Let's improve our splitting logic to be more robust:
20240613061102.sql
ALTER TABLE "users" ADD COLUMN "first_name" text NULL, ADD COLUMN "last_name" text NULL;
UPDATE "users"
SET "first_name" = regexp_replace("name", ' ([^ ]+)$', ''),
"last_name" = regexp_replace("name", '^.* ', '');
We changed our splitting logic to be more robust by using regular expressions:
- The
first_name column will now contain everything before the last space in the name column.
- The
last_name column will contain everything after the last space in the name column.
Before testing our new logic, we need to update our migration hash:
atlas migrate hash --env local
Now, let's run the test again:
atlas migrate test --env local --run name_split_middle_name
The output will be:
-- PASS: name_split_middle_name (31ms)
PASS
Great! Our test passed, and we can now be confident that our migration works as expected for names with middle names.
As a final check, let's also verify that our migration works correctly for names with only one word, such as Prince:
migrations.test.hcl
test "migrate" "name_split_one_word" {
migrate {
to = "20240613061046"
}
exec {
sql = "insert into users (name) values ('Prince')"
}
migrate {
to = "20240613061102"
}
exec {
sql = "select first_name,last_name from users"
output = "Prince, "
}
}
Let's run the test:
atlas migrate test --env local --run name_split_one_word
The output will be:
-- PASS: name_split_one_word (34ms)
PASS
Amazing! Our test passed, and we can move forward with confidence.
Enhanced Editor Support
In this release, we have added support for some long-awaited features in our VSCode and JetBrains plugins:
- Multi-file schemas - Our editor plugins will now automatically detect and load all schema files in your project, allowing
you to reference tables and columns across files.
- Jump to definition - Source code can be modeled as a graph of entities where one entity can reference another. For example
a Java class method invokes a method in another class, or a table's foreign key references another table's primary key.
Jump to definition allows you to navigate this graph by jumping to the definition of the entity you are interested in.
- Support for much larger schemas - We have improved the performance of our editor plugins to support much larger schemas.
To try the latest versions, head over to the VSCode Marketplace
or the JetBrains Marketplace.
Wrapping Up
That's all for this release! We hope you try out (and enjoy) all of these new features and find them useful.
As always, we would love to hear your feedback and suggestions on our Discord server.
