Christoph at 00:09, 30 August 2018

2018-08-30T00:09:02Z

Christoph: Created page with "'''Alembic'' is a database migrations tool written by the author of [http://www.sqlalchemy.org/ SQLAlchemy]. ==Install Alembic== ''Note: This install process was tested on Ub..."

2016-08-10T22:27:27Z

Created page with "'''Alembic'' is a database migrations tool written by the author of [http://www.sqlalchemy.org/ SQLAlchemy]. ==Install Alembic== ''Note: This install process was tested on Ub..."

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'''Alembic'' is a database migrations tool written by the author of [http://www.sqlalchemy.org/ SQLAlchemy].

==Install Alembic==
''Note: This install process was tested on Ubuntu 16.04, but it should also work on other distros just fine.''

Assuming you already have MySQL installed on your machine, get the following Alembic dependencies installed:
$ sudo apt-get install libmysqlclient-dev -y
$ sudo pip install mysql-python

Now, install Alembic:
$ sudo pip install alembic

==Configure and use Alembic==

* Create the database migrations environment (note: use "generic" if setting up a single database):
$ cd $HOME/dev
$ alembic init --template generic alembic

* Edit the <code>alembic.ini</code> (created by the above command) and change the following line to match your MySQL user, password, hostname, and database name (note: change "driver" to "mysql"):
sqlalchemy.url = driver://user:pass@localhost/dbname

* Test that alembic has been properly configured and can connect to MySQL:
$ alembic current

* If the above command did not return any errors, create your first revision:
$ alembic revision -m "Create users table"
Generating $HOME/dev/alembic/versions/9710a474efc0_create_users_table.py ... done

* Edit that <code>9710a474efc0_create_users_table.py</code> file and update the <code>upgrade()</code> and <code>downgrade()</code> functions to look like the following:
<pre>
def upgrade():
op.create_table(
'users',
sa.Column('id', sa.Integer, primary_key=True),
sa.Column('name', sa.String(50), nullable=False),
sa.Column('my_decimal', sa.Numeric(16,8), nullable=False),
sa.Column('dob', sa.DateTime, nullable=False),
)

def downgrade():
op.drop_table('users')
</pre>

* Now, run a database migration to create the above user table to "head" (where "head" is the latest available migration):
$ alembic upgrade head

* Check your MySQL database, and you should see something like the following:
$ mysql -e 'describe dbname.users;'
+------------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | | NULL | |
| my_decimal | decimal(16,8) | NO | | NULL | |
| dob | datetime | NO | | NULL | |
+------------+---------------+------+-----+---------+----------------+

* Undo that above (last) migration with:
$ alembic downgrade -1

* Delete the entire database and re-create it (note: to migrate back to the first migration {the beginning}, use "base" {the opposite of "head"}):
$ alembic downgrade base
$ alembic upgrade head

Your Alembic environment tree should look something like the following:
<pre>
.
├── alembic
│   ├── env.py
│   ├── env.pyc
│   ├── README
│   ├── script.py.mako
│   └── versions
│   ├── 9710a474efc0_create_users_table.py
│   └── 9710a474efc0_create_users_table.pyc
└── alembic.ini
</pre>

See the [http://alembic.zzzcomputing.com/en/latest/ Alembic documentation] for many more examples and details.

==External links==
* [https://bitbucket.org/zzzeek/alembic Official website]
* [http://alembic.zzzcomputing.com/en/latest/ Alembic documentation]

[[Category:Technical and Specialized Skills]]
[[Category:Linux Command Line Tools]]

← Older revision		Revision as of 00:09, 30 August 2018
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−	'''Alembic'' is a database migrations tool written by the author of [http://www.sqlalchemy.org/ SQLAlchemy].	+	''Alembic'' is a database migrations tool written by the author of [http://www.sqlalchemy.org/ SQLAlchemy].

	==Install Alembic==		==Install Alembic==

Alembic - Revision history

Christoph at 00:09, 30 August 2018

Christoph: Created page with "'''Alembic'' is a database migrations tool written by the author of [http://www.sqlalchemy.org/ SQLAlchemy]. ==Install Alembic== ''Note: This install process was tested on Ub..."