From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Tue, 4 Mar 2014 23:24:15 +0000 (-0500)
Subject: - add new section, cookbook.  First example, add conditonal sections to migrations
X-Git-Tag: rel_0_6_4~15
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=334e04d710f16a04ce4d9ed737ec2d0a02b11de4;p=thirdparty%2Fsqlalchemy%2Falembic.git

- add new section, cookbook.  First example, add conditonal sections to migrations
within script.py.mako.   fixes #177
---

diff --git a/docs/build/cookbook.rst b/docs/build/cookbook.rst
new file mode 100644
index 00000000..6a07e4dd
--- /dev/null
+++ b/docs/build/cookbook.rst
@@ -0,0 +1,144 @@
+========
+Cookbook
+========
+
+A collection of "How-Tos", highlighting various ways to extend
+Alembic.
+
+.. note::
+
+    This is a new section where we hope to start cataloguing various "how-tos"
+    we come up with based on user requests.  It is often the case that users
+    will request a feature only to learn that simple customization can
+    provide the same thing.   There's only one recipe at the moment but
+    we hope to get more soon!
+
+Conditional Migration Elements
+==============================
+
+This example features the basic idea of a common need, that of affecting
+how a migration runs based on command line switches.
+
+The technique to use here is simple; within a migration script, inspect
+the :meth:`.EnvironmentContext.get_x_argument` collection for any additional,
+user-defined parameters.  Then take action based on the presence of those
+arguments.
+
+To make it such that the logic to inspect these flags is easy to use and
+modify, we modify our ``script.py.mako`` template to make this feature
+available in all new revision files:
+
+.. code-block:: mako
+
+    """${message}
+
+    Revision ID: ${up_revision}
+    Revises: ${down_revision}
+    Create Date: ${create_date}
+
+    """
+
+    # revision identifiers, used by Alembic.
+    revision = ${repr(up_revision)}
+    down_revision = ${repr(down_revision)}
+
+    from alembic import op
+    import sqlalchemy as sa
+    ${imports if imports else ""}
+
+    from alembic import context
+
+
+    def upgrade():
+        schema_upgrades()
+        if context.get_x_argument(as_dictionary=True).get('data', None):
+            data_upgrades()
+
+    def downgrade():
+        if context.get_x_argument(as_dictionary=True).get('data', None):
+            data_downgrades()
+        schema_downgrades()
+
+    def schema_upgrades():
+        """schema upgrade migrations go here."""
+        ${upgrades if upgrades else "pass"}
+
+    def schema_downgrades():
+        """schema downgrade migrations go here."""
+        ${downgrades if downgrades else "pass"}
+
+    def data_upgrades():
+        """Add any optional data upgrade migrations here!"""
+        pass
+
+    def data_downgrades():
+        """Add any optional data downgrade migrations here!"""
+        pass
+
+Now, when we create a new migration file, the ``data_upgrades()`` and ``data_downgrades()``
+placeholders will be available, where we can add optional data migrations::
+
+    """rev one
+
+    Revision ID: 3ba2b522d10d
+    Revises: None
+    Create Date: 2014-03-04 18:05:36.992867
+
+    """
+
+    # revision identifiers, used by Alembic.
+    revision = '3ba2b522d10d'
+    down_revision = None
+
+    from alembic import op
+    import sqlalchemy as sa
+    from sqlalchemy import String, Column
+    from sqlalchemy.sql import table, column
+
+    from alembic import context
+
+    def upgrade():
+        schema_upgrades()
+        if context.get_x_argument(as_dictionary=True).get('data', None):
+            data_upgrades()
+
+    def downgrade():
+        if context.get_x_argument(as_dictionary=True).get('data', None):
+            data_downgrades()
+        schema_downgrades()
+
+    def schema_upgrades():
+        """schema upgrade migrations go here."""
+        op.create_table("my_table", Column('data', String))
+
+    def schema_downgrades():
+        """schema downgrade migrations go here."""
+        op.drop_table("my_table")
+
+    def data_upgrades():
+        """Add any optional data upgrade migrations here!"""
+
+        my_table = table('my_table',
+            column('data', String),
+        )
+
+        op.bulk_insert(my_table,
+            [
+                {'data': 'data 1'},
+                {'data': 'data 2'},
+                {'data': 'data 3'},
+            ]
+        )
+
+    def data_downgrades():
+        """Add any optional data downgrade migrations here!"""
+
+        op.execute("delete from my_table")
+
+To invoke our migrations with data included, we use the ``-x`` flag::
+
+    alembic -x data=true upgrade head
+
+The :meth:`.EnvironmentContext.get_x_argument` is an easy way to support
+new commandline options within environment and migration scripts.
+
diff --git a/docs/build/index.rst b/docs/build/index.rst
index 4e8b5360..fb7efc69 100644
--- a/docs/build/index.rst
+++ b/docs/build/index.rst
@@ -11,6 +11,7 @@ with the `SQLAlchemy <http://www.sqlalchemy.org>`_ Database Toolkit for Python.
    front
    tutorial
    ops
+   cookbook
    api
    changelog