make chapter 6 code match the walkthrough

Remove unrequested exercise solutions and additional behavior. Assemble the chapter snippets and retain only the standard Alembic scaffold and two walkthrough migrations.

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Co-authored-by: Snowflake CoCo <noreply@snowflake.com>

Author: svnv-svsv-jm

Chapter06/registration-service/README.md

@@ -1,38 +1,9 @@
 # Chapter 6: Registration Service
 
-This is the final version of the chapter's SQLAlchemy service, including the three exercises. It uses Python 3.13 and uv. Run these commands from this directory:
+This directory contains the final code from the chapter walkthrough, without exercise solutions or additional features.
 
-```bash
-uv sync
-uv run alembic upgrade head
-uv run fastapi dev main.py
-```
+From this directory, install the dependencies with `uv sync`. The final `database.py` uses the local PostgreSQL connection shown in the chapter. Start that database, run `uv run python check_db.py`, then `uv run alembic upgrade head` and `uv run fastapi dev main.py`.
 
-Open http://127.0.0.1:8000/docs to register, list, read, update, and delete users. This is a teaching example with no authentication or authorization; do not expose it publicly. Access controls are covered later in the book.
+Run the chapter's eight tests with `uv run pytest -v`. They use SQLite and do not require PostgreSQL.
 
-## Database setup
-
-SQLite is the default and needs no server. The final application does not create tables at startup: run the committed migrations before starting it against an empty database. Do not generate a second initial migration. If following the earlier `create_all` example, use a fresh database for the migration walkthrough rather than applying the initial migration to an existing `users` table.
-
-For PostgreSQL, provision a database and supply a `postgresql+asyncpg` connection URL through `DATABASE_URL` using your deployment's secret management. Never commit real credentials. Run the same migrations and `uv run python check_db.py` before starting the service. The check script also supports SQLite.
-
-The migrations create the seven-column users table, add the optional phone number, and add JSON preferences. Preferences use JSONB on PostgreSQL and JSON on SQLite. Python-side defaults are applied by SQLAlchemy, not by direct database inserts.
-
-## Tests
-
-```bash
-uv run pytest -v
-uv run ruff check .
-```
-
-Tests use temporary SQLite databases and do not connect to the configured application database. They cover the chapter's eight API cases, stored password hashing, validation, pagination, concurrent-duplicate handling, and migration upgrades/downgrades that preserve existing users. PostgreSQL integration must be checked separately against a running server.
-
-Compared with the printed snippets, the runnable service also returns 409 if a duplicate insert wins a race and rejects explicit null updates to non-nullable columns. Omitted update fields remain unchanged.
-
-## Exercises
-
-- **6.1:** `crud.get_users` and `GET /users` provide pagination ordered by user ID, with validated bounds.
-- **6.2:** `User.phone_number`, `UserBase.phone_number`, and migration `0002` add an optional phone number without deleting users.
-- **6.3:** `exercises/slot_repository.py` implements Chapter 3's `AvailabilitySlotRepository`. It imports the existing domain rather than duplicating it; pytest adds the Chapter 3 service to its Python path. The tests also run the unchanged Chapter 3 use cases against this adapter.
-
-The slot repository is synchronous because Chapter 3's repository interface is synchronous. Its separate metadata is not part of the registration database migrations. Construct it with a SQLAlchemy `sessionmaker` and inject it in place of the in-memory repository. The example does not implement concurrent reservation conflict detection.
+The Alembic scaffold comes from `alembic init -t async alembic`. Its two generated revisions create the users table and add preferences. `script.py.mako` is Alembic's standard template for generating revisions.

Chapter06/registration-service/alembic.ini

@@ -1,4 +1,149 @@
+# A generic, single database configuration.
+
 [alembic]
+# path to migration scripts.
+# this is typically a path given in POSIX (e.g. forward slashes)
+# format, relative to the token %(here)s which refers to the location of this
+# ini file
 script_location = %(here)s/alembic
-prepend_sys_path = %(here)s
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# see https://alembic.sqlalchemy.org/en/latest/tutorial.html#editing-the-ini-file
+# for all available tokens
+# file_template = %%(year)d_%%(month).2d_%%(day).2d_%%(hour).2d%%(minute).2d-%%(rev)s_%%(slug)s
+# Or organize into date-based subdirectories (requires recursive_version_locations = true)
+# file_template = %%(year)d/%%(month).2d/%%(day).2d_%%(hour).2d%%(minute).2d_%%(second).2d_%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.  for multiple paths, the path separator
+# is defined by "path_separator" below.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the tzdata library which can be installed by adding
+# `alembic[tz]` to the pip requirements.
+# string value is passed to ZoneInfo()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; This defaults
+# to <script_location>/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "path_separator"
+# below.
+# version_locations = %(here)s/bar:%(here)s/bat:%(here)s/alembic/versions
+
+# path_separator; This indicates what character is used to split lists of file
+# paths, including version_locations and prepend_sys_path within configparser
+# files such as alembic.ini.
+# The default rendered in new alembic.ini files is "os", which uses os.pathsep
+# to provide os-dependent path splitting.
+#
+# Note that in order to support legacy alembic.ini files, this default does NOT
+# take place if path_separator is not present in alembic.ini.  If this
+# option is omitted entirely, fallback logic is as follows:
+#
+# 1. Parsing of the version_locations option falls back to using the legacy
+#    "version_path_separator" key, which if absent then falls back to the legacy
+#    behavior of splitting on spaces and/or commas.
+# 2. Parsing of the prepend_sys_path option falls back to the legacy
+#    behavior of splitting on spaces, commas, or colons.
+#
+# Valid values for path_separator are:
+#
+# path_separator = :
+# path_separator = ;
+# path_separator = space
+# path_separator = newline
+#
+# Use os.pathsep. Default configuration used for new projects.
 path_separator = os
+
+
+# set to 'true' to search source files recursively
+# in each "version_locations" directory
+# new in Alembic version 1.10
+# recursive_version_locations = false
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+# database URL.  This is consumed by the user-maintained env.py script only.
+# other means of configuring database URLs may be customized within the env.py
+# file.
+sqlalchemy.url = driver://user:pass@localhost/dbname
+
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# lint with attempts to fix using "ruff" - use the module runner, against the "ruff" module
+# hooks = ruff
+# ruff.type = module
+# ruff.module = ruff
+# ruff.options = check --fix REVISION_SCRIPT_FILENAME
+
+# Alternatively, use the exec runner to execute a binary found on your PATH
+# hooks = ruff
+# ruff.type = exec
+# ruff.executable = ruff
+# ruff.options = check --fix REVISION_SCRIPT_FILENAME
+
+# Logging configuration.  This is also consumed by the user-maintained
+# env.py script only.
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+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

Chapter06/registration-service/alembic/README

@@ -0,0 +1 @@
+Generic single-database configuration with an async dbapi.

Chapter06/registration-service/alembic/env.py

@@ -1,52 +1,94 @@
 import asyncio
+from logging.config import fileConfig
 
 from sqlalchemy import pool
+from sqlalchemy.engine import Connection
 from sqlalchemy.ext.asyncio import async_engine_from_config
 
 from alembic import context
 from database import DATABASE_URL
 from models import Base
 
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
 config = context.config
-config.set_main_option(
-    "sqlalchemy.url", DATABASE_URL.replace("%", "%%")
-)
+
+# 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 = Base.metadata
+config.set_main_option("sqlalchemy.url", DATABASE_URL)
+
+# 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=DATABASE_URL,
+        url=url,
         target_metadata=target_metadata,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
     )
+
     with context.begin_transaction():
         context.run_migrations()
 
 
-def do_run_migrations(connection) -> None:
+def do_run_migrations(connection: Connection) -> None:
     context.configure(
         connection=connection, target_metadata=target_metadata
     )
+
     with context.begin_transaction():
         context.run_migrations()
 
 
 async def run_async_migrations() -> None:
+    """In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+
     connectable = async_engine_from_config(
         config.get_section(config.config_ini_section, {}),
         prefix="sqlalchemy.",
         poolclass=pool.NullPool,
     )
-    try:
-        async with connectable.connect() as connection:
-            await connection.run_sync(do_run_migrations)
-    finally:
-        await connectable.dispose()
+
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+
+    await connectable.dispose()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode."""
+
+    asyncio.run(run_async_migrations())
 
 
 if context.is_offline_mode():
     run_migrations_offline()
 else:
-    asyncio.run(run_async_migrations())
+    run_migrations_online()

Chapter06/registration-service/alembic/script.py.mako

@@ -2,20 +2,27 @@
 
 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
 ${imports if imports else ""}
 
-revision = ${repr(up_revision)}
-down_revision = ${repr(down_revision)}
-branch_labels = ${repr(branch_labels)}
-depends_on = ${repr(depends_on)}
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, Sequence[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:
+    """Upgrade schema."""
     ${upgrades if upgrades else "pass"}
 
 
 def downgrade() -> None:
+    """Downgrade schema."""
     ${downgrades if downgrades else "pass"}