### Yoyo Configuration File Example

Source: https://ollycope.com/software/yoyo/latest

Example `yoyo.ini` configuration file. Specifies migration sources, database connection, verbosity, batch mode, editor, post-create command, and filename prefix.

```ini
[DEFAULT]

# List of migration source directories. "% (here)s" is expanded to the
# full path of the directory containing this ini file.
sources = %(here)s/migrations %(here)s/lib/module/migrations

# Target database
database = postgresql://scott:tiger@localhost/mydb

# Verbosity level. Goes from 0 (least verbose) to 3 (most verbose)
verbosity = 3

# Disable interactive features
batch_mode = on

# Editor to use when starting new migrations
# "{}" is expanded to the filename of the new migration
editor = /usr/local/bin/vim -f {}

# An arbitrary command to run after a migration has been created
# "{}" is expanded to the filename of the new migration
post_create_command = hg add {}

# A prefix to use for generated migration filenames
prefix = myproject_

```

--------------------------------

### SQL Migration Content Example

Source: https://ollycope.com/software/yoyo/latest

Example content for a SQL migration file, including a comment and SQL commands.

```sql
-- Create table foo
-- depends:

CREATE TABLE foo (
     a int
);
```

--------------------------------

### MySQL Network Connection Example

Source: https://ollycope.com/software/yoyo/latest

Example configuration for a MySQL network database connection using a connection URL.

```ini
database = mysql://scott:tiger@localhost/mydatabase
```

--------------------------------

### Install yoyo-migrations

Source: https://ollycope.com/software/yoyo/latest

Install the yoyo-migrations package using pip.

```bash
pip install yoyo-migrations
```

--------------------------------

### Connect to a PostgreSQL Database

Source: https://ollycope.com/software/yoyo/latest

Example of specifying a PostgreSQL database connection URL for yoyo commands.

```bash
yoyo list --database postgresql://scott:tiger@localhost/mydatabase
```

--------------------------------

### Migration Sources Configuration

Source: https://ollycope.com/software/yoyo/latest

Configures migration sources in `yoyo.ini` using glob patterns for local directories or `package:` format for migrations within installed Python packages.

```ini
[DEFAULT]
sources =
    %(here)s/migrations
    %(here)s/src/*/migrations

```

```ini
[DEFAULT]
sources = package:myapplication:data/migrations

```

--------------------------------

### Use Custom Backend via Command Line

Source: https://ollycope.com/software/yoyo/latest

Specify your custom backend using its registered name as the protocol in the `--database` argument when running Yoyo commands. For example, `yoyo apply --database my_backend://...`.

```sh
yoyo apply --database my_backend://...
```

--------------------------------

### Import Step and Transaction in Migration Scripts

Source: https://ollycope.com/software/yoyo/latest

To prevent linters from throwing errors on undefined names in migration scripts, start your migration files with the import statement `from yoyo import step, transaction`.

```python
from yoyo import step, transaction
```

--------------------------------

### Initialize Yoyo Project

Source: https://ollycope.com/software/yoyo/latest

Initialize yoyo for your project, specifying the database connection string and migrations directory.

```bash
yoyo init --database sqlite:///mydb.sqlite3 migrations
```

--------------------------------

### Create a Basic Python Migration

Source: https://ollycope.com/software/yoyo/latest

Define migration steps using Python and the `step` function. Each step includes SQL for applying and rolling back changes.

```python
from yoyo import step
steps = [
   step(
       "CREATE TABLE foo (id INT, bar VARCHAR(20), PRIMARY KEY (id))",
       "DROP TABLE foo"
   )
]
```

--------------------------------

### Configure Custom Backend Entry Point

Source: https://ollycope.com/software/yoyo/latest

Define custom Yoyo backends by subclassing `yoyo.backends.base.DatabaseBackend` and registering them using `entry_points` in your package's `setup.cfg`. This allows you to use your custom backend with the `yoyo` command-line tool.

```ini
[options.entry_points]

yoyo.backends =
    mybackend = mypackage:MyBackend
```

--------------------------------

### Configuration File Inheritance and Includes

Source: https://ollycope.com/software/yoyo/latest

Demonstrates `%inherit` and `%include` directives in Yoyo configuration files for managing settings across multiple files. `%inherit` processes settings first, while `%include` processes later.

```ini
#
# file: yoyo-defaults.ini
#
[DEFAULT]
sources = %(here)s/migrations

#
# file: yoyo.ini
#
[DEFAULT]

; Inherit settings from yoyo-defaults.ini
; 
; Settings in inherited files are processed first and may be overridden by
; settings in this file
%inherit = yoyo-defaults.ini

; Include settings from yoyo-local.ini
; 
; Included files are processed after this file and may override the settings
; in this file
%include = yoyo-local.ini


; Use '?' to avoid raising an error if the file does not exist
%inherit = ?yoyo-defaults.ini

database = sqlite:///%(here)s/mydb.sqlite

```

--------------------------------

### Create a New Migration with Message

Source: https://ollycope.com/software/yoyo/latest

Create a new migration file with a descriptive message.

```bash
yoyo new -m "Add column to foo"
```

--------------------------------

### Create a New SQL Migration

Source: https://ollycope.com/software/yoyo/latest

Generate a new migration file in SQL format using the `yoyo new --sql` command.

```bash
yoyo new --sql
```

--------------------------------

### Yoyo Command Help

Source: https://ollycope.com/software/yoyo/latest

View the list of available yoyo commands.

```bash
$ yoyo --help
```

--------------------------------

### Migration Steps as Python Functions

Source: https://ollycope.com/software/yoyo/latest

Use Python functions for migration steps when SQL is insufficient. Each function receives a database connection object.

```python
#
# file: migrations/0001_create_foo.py
#
from yoyo import step

def apply_step(conn):
    cursor = conn.cursor()
    cursor.execute(
        # query to perform the migration
    )

def rollback_step(conn):
    cursor = conn.cursor()
    cursor.execute(
        # query to undo the above
    )

steps = [
  step(apply_step, rollback_step)
]

```

--------------------------------

### PostgreSQL Connection Strings

Source: https://ollycope.com/software/yoyo/latest

Set up PostgreSQL connections, supporting unix sockets, custom schemas, and the psycopg 3 driver.

```python
database = postgresql://scott:tiger@localhost/mydatabase
```

```python
database = postgresql://scott:tiger@/mydatabase
```

```python
database = postgresql://scott:tiger@/mydatabase?host=/var/run/postgresql&port=5434
```

```python
database = postgresql+psycopg://scott:tiger@localhost/mydatabase
```

```python
database = postgresql://scott:tiger@/mydatabase?schema=some_schema
```

--------------------------------

### List Migrations

Source: https://ollycope.com/software/yoyo/latest

Display the list of available migrations, indicating applied (A) and unapplied (U) statuses.

```bash
$ yoyo list
```

--------------------------------

### Apply Migrations

Source: https://ollycope.com/software/yoyo/latest

Apply all unapplied migrations to the target database. Batch mode can be enabled to disable prompting.

```bash
$ yoyo apply
```

--------------------------------

### MySQL Connection Strings

Source: https://ollycope.com/software/yoyo/latest

Configure MySQL connections using different drivers and options like unix sockets and SSL/TLS.

```python
database = mysql://scott:tiger@/mydatabase?unix_socket=/tmp/mysql.sock
```

```python
database = mysql+mysqldb://scott:tiger@localhost/mydatabase
```

```python
database = mysql+mysqldb://scott:tiger@localhost/mydatabase?ssl=yes&sslca=/path/to/cert
```

--------------------------------

### Apply and Rollback Migrations from Python

Source: https://ollycope.com/software/yoyo/latest

Integrate Yoyo migrations into your Python code by obtaining a backend instance and reading migration files. Use `backend.lock()` to ensure exclusive access, then apply or rollback migrations as needed.

```python
from yoyo import read_migrations
from yoyo import get_backend

backend = get_backend('postgresql://myuser@localhost/mydatabase')
migrations = read_migrations('path/to/migrations')

with backend.lock():

    # Apply any outstanding migrations
    backend.apply_migrations(backend.to_apply(migrations))

    # Rollback all migrations
    backend.rollback_migrations(backend.to_rollback(migrations))
```

--------------------------------

### SQLite Connection Strings

Source: https://ollycope.com/software/yoyo/latest

Configure SQLite connections, specifying database files or in-memory databases. Use three slashes for relative paths and four for absolute paths.

```python
sqlite:///mydb.sqlite
```

```python
sqlite:////home/user/mydb.sqlite
```

--------------------------------

### Post-Apply Hook Script

Source: https://ollycope.com/software/yoyo/latest

A special migration file named `post-apply.py` or `post-apply.sql` that runs after every successful migration. Useful for tasks like updating permissions or re-creating views.

```python
# This is a placeholder for a post-apply hook script. 
# Actual content would be Python code to execute after migrations.
pass

```

--------------------------------

### SQL Migration Script

Source: https://ollycope.com/software/yoyo/latest

Standard SQL script for applying a database migration. Save as `<migration-name>.sql`.

```sql
--
-- file: migrations/0001.create-foo.sql
--
CREATE TABLE foo (id INT, bar VARCHAR(20), PRIMARY KEY (id));

```

--------------------------------

### Grouped Migration Steps with Error Handling

Source: https://ollycope.com/software/yoyo/latest

Use `group` to nest migration steps and control rollback behavior. `ignore_errors='all'` will roll back only the failed step, allowing execution to continue with the next step. If `ignore_errors` is not set, the entire migration rolls back on error.

```python
group([
  step("ALTER TABLE employees ADD tax_code TEXT"),
  step("CREATE INDEX tax_code_idx ON employees (tax_code)")
], ignore_errors='all')
step("UPDATE employees SET tax_code='C' WHERE pay_grade < 4")
step("UPDATE employees SET tax_code='B' WHERE pay_grade >= 6")
step("UPDATE employees SET tax_code='A' WHERE pay_grade >= 8")
```

--------------------------------

### Python Migration Script Structure

Source: https://ollycope.com/software/yoyo/latest

Define database migrations using Python scripts with steps for applying and rolling back changes. Supports SQL queries or Python functions.

```python
#
# file: migrations/0001_create_foo.py
#
from yoyo import step

__depends__ = {"0000.initial-schema"}

steps = [
  step(
      "CREATE TABLE foo (id INT, bar VARCHAR(20), PRIMARY KEY (id))",
      "DROP TABLE foo",
  ),
  step(
      "ALTER TABLE foo ADD COLUMN baz INT NOT NULL"
  )
]

```

--------------------------------

### SQL Migration with Dependencies

Source: https://ollycope.com/software/yoyo/latest

SQL script specifying dependencies on other migrations using a structured comment. The `depends:` directive lists space-separated migration names.

```sql
-- depends: 0000.initial-schema 0001.create-foo

ALTER TABLE foo ADD baz INT;

```

--------------------------------

### SQL Rollback Script

Source: https://ollycope.com/software/yoyo/latest

SQL script for rolling back a database migration. Save as `<migration-name>.rollback.sql`.

```sql
--
-- file: migrations/0001.create-foo.rollback.sql
--
DROP TABLE foo;

```

--------------------------------

### Configure Mercurial for Email Commits

Source: https://ollycope.com/software/yoyo/latest

Set up your Mercurial configuration (`~/.hgrc`) to use the `patchbomb` extension and configure SMTP settings for sending commits via email. This is part of the contribution workflow for Yoyo.

```ini
[extensions]
patchbomb = 

[email]
from = Your Name <you@example.org>
method = smtp

[smtp]
host = mail.example.org
port = 587
tls = smtps
username = you@example.org
```

--------------------------------

### Migration Dependencies

Source: https://ollycope.com/software/yoyo/latest

Declare dependencies between migration scripts using the `__depends__` attribute to ensure correct execution order.

```python
#
# file: migrations/0002.modify-foo.py
#
__depends__ = {'0000.initial-schema', '0001.create-foo'}

steps = [
  # migration steps
]


```

--------------------------------

### Update Yoyo Imports for Namespace Package Removal

Source: https://ollycope.com/software/yoyo/latest

When migrating from older versions of Yoyo, update your import statements to reflect the removal of the yoyo.migrate namespace package. This ensures compatibility with newer versions.

```python
from yoyo.migrate import read_migrations
from yoyo.migrate.connections import connect
```

```python
from yoyo import read_migrations
from yoyo.connections import connect
```

--------------------------------

### Set Local Mercurial Email Recipient

Source: https://ollycope.com/software/yoyo/latest

Configure the local repository's Mercurial settings (`.hg/hgrc`) to specify the recipient address for sending commits via email. This ensures your commits are sent to the correct mailing list for review.

```ini
[email]
to = <~olly/yoyo@lists.sr.ht>
```

--------------------------------

### Disable Transactions in SQL Migration

Source: https://ollycope.com/software/yoyo/latest

Use the `-- transactional: false` directive at the beginning of an SQL migration file to disable transaction handling for that migration. This is necessary for certain SQL statements that are not permitted within transaction blocks.

```sql
-- transactional: false

CREATE DATABASE mydb
```

--------------------------------

### Disable Transactions in Python Migration

Source: https://ollycope.com/software/yoyo/latest

Set `__transactional__ = False` within a Python migration script to disable transaction handling for all steps in that migration. This is useful for statements that cannot be run inside a transaction block, like `CREATE DATABASE`.

```python
__transactional__ = False

step("CREATE DATABASE mydb", "DROP DATABASE mydb")
```

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