A bit of an autodetector and a bit of a writer

django/db/migrations/writer.py

@@ -0,0 +1,123 @@
+import datetime
+import types
+
+
+class MigrationWriter(object):
+    """
+    Takes a Migration instance and is able to produce the contents
+    of the migration file from it.
+    """
+
+    def __init__(self, migration):
+        self.migration = migration
+
+    def as_string(self):
+        """
+        Returns a string of the file contents.
+        """
+        items = {
+            "dependencies": repr(self.migration.dependencies),
+        }
+        imports = set()
+        # Deconstruct operations
+        operation_strings = []
+        for operation in self.migration.operations:
+            name, args, kwargs = operation.deconstruct()
+            arg_strings = []
+            for arg in args:
+                arg_string, arg_imports = self.serialize(arg)
+                arg_strings.append(arg_string)
+                imports.update(arg_imports)
+            for kw, arg in kwargs.items():
+                arg_string, arg_imports = self.serialize(arg)
+                imports.update(arg_imports)
+                arg_strings.append("%s = %s" % (kw, arg_string))
+            operation_strings.append("migrations.%s(%s\n        )" % (name, "".join("\n            %s," % arg for arg in arg_strings)))
+        items["operations"] = "[%s\n    ]" % "".join("\n        %s," % s for s in operation_strings)
+        # Format imports nicely
+        if not imports:
+            items["imports"] = ""
+        else:
+            items["imports"] = "\n".join(imports) + "\n"
+        return MIGRATION_TEMPLATE % items
+
+    @property
+    def filename(self):
+        return "%s.py" % self.migration.name
+
+    @classmethod
+    def serialize(cls, value):
+        """
+        Serializes the value to a string that's parsable by Python, along
+        with any needed imports to make that string work.
+        More advanced than repr() as it can encode things
+        like datetime.datetime.now.
+        """
+        # Sequences
+        if isinstance(value, (list, set, tuple)):
+            imports = set()
+            strings = []
+            for item in value:
+                item_string, item_imports = cls.serialize(item)
+                imports.update(item_imports)
+                strings.append(item_string)
+            if isinstance(value, set):
+                format = "set([%s])"
+            elif isinstance(value, tuple):
+                format = "(%s,)"
+            else:
+                format = "[%s]"
+            return format % (", ".join(strings)), imports
+        # Dictionaries
+        elif isinstance(value, dict):
+            imports = set()
+            strings = []
+            for k, v in value.items():
+                k_string, k_imports = cls.serialize(k)
+                v_string, v_imports = cls.serialize(v)
+                imports.update(k_imports)
+                imports.update(v_imports)
+                strings.append((k_string, v_string))
+            return "{%s}" % (", ".join(["%s: %s" % (k, v) for k, v in strings])), imports
+        # Datetimes
+        elif isinstance(value, (datetime.datetime, datetime.date)):
+            return repr(value), set(["import datetime"])
+        # Simple types
+        elif isinstance(value, (int, long, float, str, unicode, bool, types.NoneType)):
+            return repr(value), set()
+        # Functions
+        elif isinstance(value, (types.FunctionType, types.BuiltinFunctionType)):
+            # Special-cases, as these don't have im_class
+            special_cases = [
+                (datetime.datetime.now, "datetime.datetime.now", ["import datetime"]),
+                (datetime.datetime.utcnow, "datetime.datetime.utcnow", ["import datetime"]),
+                (datetime.date.today, "datetime.date.today", ["import datetime"]),
+            ]
+            for func, string, imports in special_cases:
+                if func == value:  # For some reason "utcnow is not utcnow"
+                    return string, set(imports)
+            # Method?
+            if hasattr(value, "im_class"):
+                klass = value.im_class
+                module = klass.__module__
+                return "%s.%s.%s" % (module, klass.__name__, value.__name__), set(["import %s" % module])
+            else:
+                module = value.__module__
+                if module is None:
+                    raise ValueError("Cannot serialize function %r: No module" % value)
+                return "%s.%s" % (module, value.__name__), set(["import %s" % module])
+        # Uh oh.
+        else:
+            raise ValueError("Cannot serialize: %r" % value)
+
+
+MIGRATION_TEMPLATE = """# encoding: utf8
+from django.db import models, migrations
+%(imports)s
+
+class Migration(migrations.Migration):
+
+    dependencies = %(dependencies)s
+
+    operations = %(operations)s
+"""