✨ Docs: Schema Migrations with Alembic

Author: ryankwondev

docs/advanced/migrations.md

@@ -0,0 +1,98 @@
+# Schema Migrations using Alembic
+
+SQLModel integrates with [Alembic](https://alembic.sqlalchemy.org/) to handle schema migrations.
+Alembic is a lightweight database migration tool for usage with SQLAlchemy.
+Since SQLModel is built on top of SQLAlchemy, it's easy to use Alembic with SQLModel.
+
+## Installation
+
+To use Alembic with SQLModel, first install it:
+
+<div class="termy">
+
+```console
+$ pip install alembic
+---> 100%
+Successfully installed alembic
+```
+
+</div>
+
+Then, initialize Alembic in your project directory:
+
+```console
+alembic init migrations
+```
+
+This will create a directory named `migrations` and a configuration file named `alembic.ini`.
+
+/// info
+
+`migrations` is the directory where Alembic will store the migration scripts.
+You can choose any other name for this directory, but `migrations` is a common convention.
+
+///
+
+## Integration
+
+By making `class Table(SQLModel, table=true)`, you can add tables' information to SQLModel(SQLAlchemy) Metadata.
+
+/// info
+
+Metadata is a container object that keeps together many different features of a database.
+You can access [Working with Database Metadata](https://docs.sqlalchemy.org/en/20/core/metadata.html) for more information.
+
+///
+
+Import SQLModel on `./migrations/script.py.mako` and add the following code:
+
+```python hl_lines="12"
+{!./docs_src/advanced/migrations/tutorial001._py[ln:1-17]!}
+
+# More code here later 👇
+```
+
+/// details | 👀 Full file preview
+
+```Python hl_lines="12"
+{!./docs_src/advanced/migrations/tutorial001._py!}
+```
+
+///
+
+Next, load your models and set the target metadata on `./migrations/env.py`.
+
+```python hl_lines="7  9  24"
+{!./docs_src/advanced/migrations/tutorial002._py[ln:1-29]!}
+
+(...)
+```
+
+Lastly, set the database connection string in `./alembic.ini`.
+
+```python
+# around line 63
+sqlalchemy.url = driver://user:pass@localhost/dbname
+```
+
+## Revise and Upgrade
+
+After setting up Alembic, you can create a new revision:
+
+```console
+alembic revision --autogenerate -m "create table"
+```
+
+This will create a new revision file in `./migrations/versions/`.
+
+To apply the new revision and update the database schema, run:
+
+```console
+alembic upgrade head
+```
+
+/// tip
+
+Remember to run `alembic upgrade head` to update the remote database's schema.
+
+///

docs_src/advanced/migrations/__init__.py

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+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+import sqlmodel
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}

docs_src/advanced/migrations/tutorial001._py

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+from logging.config import fileConfig
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+from sqlmodel import SQLModel
+
+from app.models import *
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+target_metadata = SQLModel.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection, target_metadata=target_metadata
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

docs_src/advanced/migrations/tutorial002._py

@@ -99,6 +99,7 @@ nav:
   - Advanced User Guide:
     - advanced/index.md
     - advanced/decimal.md
+    - advanced/migrations.md
   - alternatives.md
   - help.md
   - contributing.md