Do not generate a migration if no schema changes are found

flask_migrate/__init__.py

@@ -1,4 +1,5 @@
 import os
+import argparse
 from flask import current_app
 from flask.ext.script import Manager
 from alembic import __version__ as __alembic_version__
@@ -17,8 +18,10 @@ def __init__(self, db, directory, **kwargs):
 
     @property
     def metadata(self):
-        """Backwards compatibility, in old releases app.extensions['migrate']
-        was set to db, and env.py accessed app.extensions['migrate'].metadata"""
+        """
+        Backwards compatibility, in old releases app.extensions['migrate']
+        was set to db, and env.py accessed app.extensions['migrate'].metadata
+        """
         return self.db.metadata
 
 
@@ -39,14 +42,16 @@ def get_template_directory(self):
         return os.path.join(package_dir, 'templates')
 
 
-def _get_config(directory, x_arg=None):
+def _get_config(directory, x_arg=None, opts=None):
     if directory is None:
         directory = current_app.extensions['migrate'].directory
     config = Config(os.path.join(directory, 'alembic.ini'))
     config.set_main_option('script_location', directory)
+    if config.cmd_opts is None:
+        config.cmd_opts = argparse.Namespace()
+    for opt in opts or []:
+        setattr(config.cmd_opts, opt, True)
     if x_arg is not None:
-        if config.cmd_opts is None:
-            config.cmd_opts = lambda: None
         if not getattr(config.cmd_opts, 'x', None):
             setattr(config.cmd_opts, 'x', [x_arg])
         else:
@@ -143,7 +148,7 @@ def revision(directory=None, message=None, autogenerate=False, sql=False,
 def migrate(directory=None, message=None, sql=False, head='head', splice=False,
             branch_label=None, version_path=None, rev_id=None):
     """Alias for 'revision --autogenerate'"""
-    config = _get_config(directory)
+    config = _get_config(directory, opts=['autogenerate'])
     if alembic_version >= (0, 7, 0):
         command.revision(config, message, autogenerate=True, sql=sql, head=head,
                          splice=splice, branch_label=branch_label,

flask_migrate/templates/flask-multidb/env.py

@@ -87,9 +87,23 @@ def run_migrations_online():
 
     """
 
+    # this callback is used to prevent an auto-migration from being generated
+    # when there are no changes to the schema
+    # reference: http://alembic.readthedocs.org/en/latest/cookbook.html
+    def process_revision_directives(context, revision, directives):
+        if getattr(config.cmd_opts, 'autogenerate', False):
+            script = directives[0]
+            if len(script.upgrade_ops_list) >= len(bind_names) + 1:
+                empty = True
+                for upgrade_ops in script.upgrade_ops_list:
+                    if not upgrade_ops.is_empty():
+                        empty = False
+                if empty:
+                    directives[:] = []
+                    logger.info('No changes in schema detected.')
+
     # for the direct-to-DB use case, start a transaction on all
     # engines, then run all migrations, then commit all transactions.
-
     engines = {'': {'engine': engine_from_config(
         config.get_section(config.config_ini_section),
         prefix='sqlalchemy.',
@@ -117,7 +131,9 @@ def run_migrations_online():
                 connection=rec['connection'],
                 upgrade_token="%s_upgrades" % name,
                 downgrade_token="%s_downgrades" % name,
-                target_metadata=get_metadata(name)
+                target_metadata=get_metadata(name),
+                process_revision_directives=process_revision_directives,
+                **current_app.extensions['migrate'].configure_args
             )
             context.run_migrations(engine_name=name)
 

flask_migrate/templates/flask/env.py

@@ -2,6 +2,7 @@
 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.
@@ -10,13 +11,15 @@
 # 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'))
+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,
@@ -51,13 +54,25 @@ def run_migrations_online():
     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.readthedocs.org/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:
@@ -70,4 +85,3 @@ def run_migrations_online():
     run_migrations_offline()
 else:
     run_migrations_online()
-

tests/app.py

@@ -1,3 +1,4 @@
+#!/bin/env python
 from flask import Flask
 from flask_sqlalchemy import SQLAlchemy
 from flask_script import Manager

tests/app_multidb.py

@@ -1,3 +1,4 @@
+#!/bin/env python
 from flask import Flask
 from flask_sqlalchemy import SQLAlchemy
 from flask_script import Manager