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Setting up FastAPI, Ormar and Alembic
If you're reading this, chances are you are already familiar with FastAPI and SQLAlchemy. Still, I'll give a slight introduction to both these libraries.
FastAPI is the 3rd most popular python web framework. The factors like asynchronous views, easy to learn, and fast setup have contributed to its quick adoption.
SQLAlchemy is the Python SQL toolkit and Object Relational Mapper that gives application developers the full power and flexibility of SQL.
It provides a full suite of well-known enterprise-level persistence patterns, designed for efficient and high-performing database access, adapted into a simple and Pythonic domain language. - from official docs
It is the most popular ORM for python, mostly seen in use with Flask.
If you have read my post, Pydantic for FastAPI, you will understand how pydantic is very useful for your FastAPI application.
SQLAlchemy uses alembic for migrations. Since ormar is built on top of sqlalchemy, we can use the same for migrations.
⚠️ The project pydantic and my Twitter handle @pydantic are not associated, just saying.
$ mkdir fastapi-ormar-alembic && cd $_
$ mkdir .venv
$ pipenv install fastapi uvicorn ormar alembic aiosqlite⚠️ Pinned dependencies are available in the Piplock file in the source code repository.
Create a new file,
db.py, in the root of the project. This file will contain the database setup and an example table.import databases
import ormar
import sqlalchemy
database = databases.Database("sqlite:///db.sqlite")
metadata = sqlalchemy.MetaData()
class BaseMeta(ormar.ModelMeta):
database = database
metadata = metadata
class Users(ormar.Model):
class Meta(BaseMeta):
tablename = "users"
id: int = ormar.Integer(primary_key=True)
email: str = ormar.String(max_length=64, unique=True)
password: str = ormar.String(max_length=128)Creating a
BaseMeta lets you add the database and metadata variables to all your models. We created a simple model with three basic fields, now let's set up migrations with alembic.
(fastapi-ormar-alembic) $ alembic init migrationsYour project structure should look like this:
├── Pipfile
├── Pipfile.lock
├── alembic.ini
├── db.py
├── db.sqlite
├── main.py
└── migrationsAdd the database URL to the
alembic.ini file. You're actually modifying a single like:sqlalchemy.url = sqlite:///db.sqliteNow, tell the migration environment where our metadata is stored. Add(modify) the following in
migrations/env.py:...
from db import BaseMeta
...
target_metadata = BaseMeta.metadataFinally, create the migration script. You can use the
--autogenerate option to generate migrations based on the metadata automatically:(fastapi-ormar-alembic) $ alembic revision --autogenerate -m "Added users table"
INFO [alembic.runtime.migration] Context impl SQLiteImpl.
INFO [alembic.runtime.migration] Will assume non-transactional DDL.
INFO [alembic.autogenerate.compare] Detected added table 'users'
Generating /home/amalshaji/Workspace/Python/blog-code-repository/fastapi-ormar-
alembic/migrations/versions/c07fe5d55962_added_users_table.py ... doneNow, run migrations:
(fastapi-ormar-alembic) $ alembic upgrade headThis produced a new file,
migrations/versions/c07fe5d55962_added_users_table.pyFile name inferred from the migration output.
"""Added users table
Revision ID: c07fe5d55962
Revises:
Create Date: 2021-08-14 11:55:46.845709
"""
from alembic import op
import sqlalchemy as sa
# revision identifiers, used by Alembic.
revision = 'c07fe5d55962'
down_revision = None
branch_labels = None
depends_on = None
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.create_table('users',
sa.Column('id', sa.Integer(), nullable=False),
sa.Column('email', sa.String(length=64), nullable=False),
sa.Column('password', sa.String(length=128), nullable=False),
sa.PrimaryKeyConstraint('id'),
sa.UniqueConstraint('email')
)
# ### end Alembic commands ###
def downgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.drop_table('users')
# ### end Alembic commands ###It worked as expected. Now let's modify our table to add a new field and run migration.
# db.py
class Users(ormar.Model):
class Meta(BaseMeta):
tablename = "users"
id: int = ormar.Integer(primary_key=True)
email: str = ormar.String(max_length=64, unique=True)
password: str = ormar.String(max_length=128)
is_active: bool = ormar.Boolean(default=True) # newRun the migration:
(fastapi-ormar-alembic) $ alembic revision --autogenerate -m "Added is_active to users table"
INFO [alembic.runtime.migration] Context impl SQLiteImpl.
INFO [alembic.runtime.migration] Will assume non-transactional DDL.
INFO [alembic.autogenerate.compare] Detected added column 'users.is_active'
Generating /home/amalshaji/Workspace/Python/blog-code-repository/fastapi-ormar-
alembic/migrations/versions/026a9a23ebbe_added_is_active_to_users_table.py ... done
(fastapi-ormar-alembic) $ alembic upgrade headThis created a new file,
migrations/versions/026a9a23ebbe_added_is_active_to_users_table.py:"""Added is_active to users table
Revision ID: 026a9a23ebbe
Revises: c07fe5d55962
Create Date: 2021-08-14 12:20:36.817128
"""
from alembic import op
import sqlalchemy as sa
# revision identifiers, used by Alembic.
revision = '026a9a23ebbe'
down_revision = 'c07fe5d55962'
branch_labels = None
depends_on = None
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.add_column('users', sa.Column('is_active', sa.Boolean(), nullable=True))
# ### end Alembic commands ###
def downgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.drop_column('users', 'is_active')
# ### end Alembic commands ###Lets verify the same by checking the database schema:
$ sqlite3 db.sqlite
SQLite version 3.31.1 2020-01-27 19:55:54
Enter ".help" for usage hints.
sqlite> .schema users
CREATE TABLE users (
id INTEGER NOT NULL,
email VARCHAR(64) NOT NULL,
password VARCHAR(128) NOT NULL, is_active BOOLEAN,
PRIMARY KEY (id),
UNIQUE (email)
);
sqlite> .quitNow that we have seen how to set up ormar + alembic let's see how to initialize our database connection in the fastapi application.
from fastapi import FastAPI
from db import database
app = FastAPI()
@app.on_event("startup")
async def startup():
if not database.is_connected:
await database.connect()
@app.on_event("shutdown")
async def shutdown():
if database.is_connected:
await database.disconnect()We used the FastAPI's(Starlette's) startup and shutdown events to create/close database connection. Actually, we are creating a connection pool. Whenever a database connection is created, it is added to the pool so that the connection can later use it for another request. Essentially removing the time taken to create a new connection.
Let's say you have a
db.py with the following BaseMeta definition....
class BaseMeta(ormar.ModelMeta):
database = database
metadata = metadata
...Add ormar models in different files.
accounts/models.py
class Users(ormar.Model):
class Meta(BaseMeta):
tablename = "users"
...posts/models.py
class Posts(ormar.Model):
class Meta(BaseMeta):
tablename = "posts"
...Inorder for the automatic migration to work, you need to import the models in your
env.py...
from accounts.models import Users
from posts.models import Posts
from db import BaseMeta
...
target_metadata = BaseMeta.metadataSource Code: fastapi-ormar-alembic
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