support EMPTY parameter

migra/command.py

@@ -3,11 +3,21 @@ from __future__ import unicode_literals, print_function
 from sqlbag import S
 import argparse
 import sys
+from contextlib import contextmanager
 
 from .migra import Migration
 from .statements import UnsafeMigrationException
 
 
+@contextmanager
+def arg_context(x):
+    if x == 'EMPTY':
+        yield None
+    else:
+        with S(x) as s:
+            yield s
+
+
 def parse_args(args):
     parser = argparse.ArgumentParser(
         description='Generate a database migration.')
@@ -36,8 +46,10 @@ def run(args, out=None, err=None):
     if not err:
         err = sys.stderr  # pragma: no cover
 
-    with S(args.dburl_from) as s0, S(args.dburl_target) as s1:
-        m = Migration(s0, s1)
+    with \
+            arg_context(args.dburl_from) as ac0, \
+            arg_context(args.dburl_target) as ac1:
+        m = Migration(ac0, ac1)
 
         if args.unsafe:
             m.set_safety(False)

migra/migra.py

@@ -1,23 +1,29 @@
 from __future__ import unicode_literals
 
 from sqlbag import raw_execute
-from schemainspect import get_inspector
+from schemainspect import get_inspector, DBInspector
 from .changes import Changes
 from .statements import Statements
 
 
 class Migration(object):
-    def __init__(self, s_from, s_target):
-        self.s_from = s_from
-        self.s_target = s_target
-
+    def __init__(self, x_from, x_target):
+        self.statements = Statements()
         self.changes = Changes(None, None)
-        self.inspect_from()
-        self.inspect_target()
-        self.statements = Statements()
 
-    def clear(self):
-        self.statements = Statements()
+        if isinstance(x_from, DBInspector):
+            self.changes.i_from = x_from
+        else:
+            self.changes.i_from = get_inspector(x_from)
+            if x_from:
+                self.s_from = x_from
+
+        if isinstance(x_target, DBInspector):
+            self.changes.i_target = x_target
+        else:
+            self.changes.i_target = get_inspector(x_target)
+            if x_target:
+                self.s_target = x_target
 
     def inspect_from(self):
         self.changes.i_from = get_inspector(self.s_from)
@@ -25,11 +31,14 @@ class Migration(object):
     def inspect_target(self):
         self.changes.i_target = get_inspector(self.s_target)
 
+    def clear(self):
+        self.statements = Statements()
+
     def apply(self):
         for stmt in self.statements:
             raw_execute(self.s_from, stmt)
 
-        self.inspect_from()
+        self.changes.i_from = get_inspector(self.s_from)
         safety_on = self.statements.safe
         self.clear()
         self.set_safety(safety_on)

setup.py

@@ -8,7 +8,7 @@ readme = io.open('README.rst').read()
 
 setup(
     name='migra',
-    version='0.1.1470919405',
+    version='0.1.1470919406',
     url='https://github.com/djrobstep/migra',
     description='Like diff but for PostgreSQL schemas',
     long_description=readme,

tests/FIXTURES/expected.sql

@@ -1,6 +1,6 @@
-create extension "citext" with schema "public" version '1.1';
+create extension "citext" with schema "public" version '1.3';
 
-create extension "hstore" with schema "public" version '1.3';
+create extension "hstore" with schema "public" version '1.4';
 
 create type "public"."bug_status" as enum ('new', 'open', 'closed');
 

tests/test_migra.py

@@ -7,7 +7,7 @@ from pytest import raises
 from migra import Statements, UnsafeMigrationException, Migration
 from migra.command import run
 from sqlbag import temporary_database, S, load_sql_from_file
-
+from schemainspect import get_inspector
 from migra.command import parse_args
 
 SQL = """select 1;
@@ -70,6 +70,8 @@ def test_all():
 
         with S(d0) as s0, S(d1) as s1:
             m = Migration(s0, s1)
+            m.inspect_from()
+            m.inspect_target()
 
             with raises(AttributeError):
                 m.changes.nonexist
@@ -89,3 +91,25 @@ def test_all():
 
         out, err = outs()
         assert run(args, out=out, err=err) == 0
+
+        # test alternative parameters
+
+        with S(d0) as s0, S(d1) as s1:
+            m = Migration(
+                get_inspector(s0),
+                get_inspector(s1)
+            )
+
+        # test empty
+        m = Migration(None, None)
+        m.add_all_changes()
+
+        with raises(AttributeError):
+            m.s_from
+
+        with raises(AttributeError):
+            m.s_target
+
+        args = parse_args(['--unsafe', 'EMPTY', 'EMPTY'])
+        out, err = outs()
+        assert run(args, out=out, err=err) == 0

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py27,py35
+envlist = py27,py36
 toxworkdir = {homedir}/.toxfiles{toxinidir}
 
 [testenv]