Chapter 4: Database (v0.4)

app/__init__.py

@@ -1,7 +1,11 @@
 from flask import Flask
+from flask_sqlalchemy import SQLAlchemy
+from flask_migrate import Migrate
 from config import Config
 
 app = Flask(__name__)
 app.config.from_object(Config)
+db = SQLAlchemy(app)
+migrate = Migrate(app, db)
 
-from app import routes
+from app import routes, models

app/models.py

@@ -0,0 +1,24 @@
+from datetime import datetime
+from app import db
+
+
+class User(db.Model):
+    id = db.Column(db.Integer, primary_key=True)
+    username = db.Column(db.String(64), index=True, unique=True)
+    email = db.Column(db.String(120), index=True, unique=True)
+    password_hash = db.Column(db.String(128))
+    posts = db.relationship('Post', back_populates='author', lazy='dynamic')
+
+    def __repr__(self):
+        return '<User {}>'.format(self.username)
+
+
+class Post(db.Model):
+    id = db.Column(db.Integer, primary_key=True)
+    body = db.Column(db.String(140))
+    timestamp = db.Column(db.DateTime, index=True, default=datetime.utcnow)
+    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), index=True)
+    author = db.relationship('User', back_populates='posts')
+
+    def __repr__(self):
+        return '<Post {}>'.format(self.body)

config.py

@@ -1,4 +1,8 @@
 import os
+basedir = os.path.abspath(os.path.dirname(__file__))
+
 
 class Config(object):
     SECRET_KEY = os.environ.get('SECRET_KEY') or 'you-will-never-guess'
+    SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL') or \
+        'sqlite:///' + os.path.join(basedir, 'app.db')

microblog.py

@@ -1 +1,7 @@
-from app import app
+from app import app, db
+from app.models import User, Post
+
+
+@app.shell_context_processor
+def make_shell_context():
+    return {'db': db, 'User': User, 'Post': Post}

migrations/README

@@ -0,0 +1 @@
+Generic single-database configuration.

migrations/alembic.ini

@@ -0,0 +1,45 @@
+# A generic, single database configuration.
+
+[alembic]
+# template used to generate migration files
+# file_template = %%(rev)s_%%(slug)s
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

migrations/env.py

@@ -0,0 +1,87 @@
+from __future__ import with_statement
+from alembic import context
+from sqlalchemy import engine_from_config, pool
+from logging.config import fileConfig
+import logging
+
+# 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.
+fileConfig(config.config_file_name)
+logger = logging.getLogger('alembic.env')
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+from flask import current_app
+config.set_main_option('sqlalchemy.url',
+                       current_app.config.get('SQLALCHEMY_DATABASE_URI'))
+target_metadata = current_app.extensions['migrate'].db.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():
+    """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)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online():
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+
+    # this callback is used to prevent an auto-migration from being generated
+    # when there are no changes to the schema
+    # reference: http://alembic.zzzcomputing.com/en/latest/cookbook.html
+    def process_revision_directives(context, revision, directives):
+        if getattr(config.cmd_opts, 'autogenerate', False):
+            script = directives[0]
+            if script.upgrade_ops.is_empty():
+                directives[:] = []
+                logger.info('No changes in schema detected.')
+
+    engine = engine_from_config(config.get_section(config.config_ini_section),
+                                prefix='sqlalchemy.',
+                                poolclass=pool.NullPool)
+
+    connection = engine.connect()
+    context.configure(connection=connection,
+                      target_metadata=target_metadata,
+                      process_revision_directives=process_revision_directives,
+                      **current_app.extensions['migrate'].configure_args)
+
+    try:
+        with context.begin_transaction():
+            context.run_migrations()
+    finally:
+        connection.close()
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

migrations/script.py.mako

@@ -0,0 +1,24 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade():
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade():
+    ${downgrades if downgrades else "pass"}

migrations/versions/780739b227a7_posts_table.py

@@ -0,0 +1,43 @@
+"""posts table
+
+Revision ID: 780739b227a7
+Revises: e517276bb1c2
+Create Date: 2017-09-11 12:23:25.496587
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '780739b227a7'
+down_revision = 'e517276bb1c2'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('post',
+    sa.Column('id', sa.Integer(), nullable=False),
+    sa.Column('body', sa.String(length=140), nullable=True),
+    sa.Column('timestamp', sa.DateTime(), nullable=True),
+    sa.Column('user_id', sa.Integer(), nullable=True),
+    sa.ForeignKeyConstraint(['user_id'], ['user.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+    with op.batch_alter_table('post', schema=None) as batch_op:
+        batch_op.create_index(batch_op.f('ix_post_timestamp'), ['timestamp'], unique=False)
+        batch_op.create_index(batch_op.f('ix_post_user_id'), ['user_id'], unique=False)
+
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('post', schema=None) as batch_op:
+        batch_op.drop_index(batch_op.f('ix_post_user_id'))
+        batch_op.drop_index(batch_op.f('ix_post_timestamp'))
+
+    op.drop_table('post')
+    # ### end Alembic commands ###

migrations/versions/e517276bb1c2_users_table.py

@@ -0,0 +1,42 @@
+"""users table
+
+Revision ID: e517276bb1c2
+Revises: 
+Create Date: 2017-09-11 11:23:05.566844
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'e517276bb1c2'
+down_revision = None
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('user',
+    sa.Column('id', sa.Integer(), nullable=False),
+    sa.Column('username', sa.String(length=64), nullable=True),
+    sa.Column('email', sa.String(length=120), nullable=True),
+    sa.Column('password_hash', sa.String(length=128), nullable=True),
+    sa.PrimaryKeyConstraint('id')
+    )
+    with op.batch_alter_table('user', schema=None) as batch_op:
+        batch_op.create_index(batch_op.f('ix_user_email'), ['email'], unique=True)
+        batch_op.create_index(batch_op.f('ix_user_username'), ['username'], unique=True)
+
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('user', schema=None) as batch_op:
+        batch_op.drop_index(batch_op.f('ix_user_username'))
+        batch_op.drop_index(batch_op.f('ix_user_email'))
+
+    op.drop_table('user')
+    # ### end Alembic commands ###