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south / south / management / commands / startmigration.py

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"""
Startmigration command, version 2.
"""

import sys
import os
import re
import string
import random
import inspect
import parser
from optparse import make_option

from django.core.management.base import BaseCommand
from django.core.management.color import no_style
from django.db import models
from django.db.models.fields.related import RECURSIVE_RELATIONSHIP_CONSTANT
from django.contrib.contenttypes.generic import GenericRelation
from django.db.models.fields import FieldDoesNotExist
from django.conf import settings

try:
    set
except NameError:
    from sets import Set as set

from south import migration, modelsinspector


class Command(BaseCommand):
    option_list = BaseCommand.option_list + (
        make_option('--model', action='append', dest='added_model_list', type='string',
            help='Generate a Create Table migration for the specified model.  Add multiple models to this migration with subsequent --model parameters.'),
        make_option('--add-field', action='append', dest='added_field_list', type='string',
            help='Generate an Add Column migration for the specified modelname.fieldname - you can use this multiple times to add more than one column.'),
        make_option('--initial', action='store_true', dest='initial', default=False,
            help='Generate the initial schema for the app.'),
        make_option('--auto', action='store_true', dest='auto', default=False,
            help='Attempt to automatically detect differences from the last migration.'),
        make_option('--freeze', action='append', dest='freeze_list', type='string',
            help='Freeze the specified model(s). Pass in either an app name (to freeze the whole app) or a single model, as appname.modelname.'),
        make_option('--stdout', action='store_true', dest='stdout', default=False,
            help='Print the migration to stdout instead of writing it to a file.'),
    )
    help = "Creates a new template migration for the given app"
    usage_str = "Usage: ./manage.py startmigration appname migrationname [--initial] [--auto] [--model ModelName] [--add-field ModelName.field_name] [--freeze] [--stdout]"
    
    def handle(self, app=None, name="", added_model_list=None, added_field_list=None, initial=False, freeze_list=None, auto=False, stdout=False, **options):
        
        # Any supposed lists that are None become empty lists
        added_model_list = added_model_list or []
        added_field_list = added_field_list or []
        
        # --stdout means name = -
        if stdout:
            name = "-"
        
        # Make sure options are compatable
        if initial and (added_model_list or added_field_list or auto):
            print "You cannot use --initial and other options together"
            print self.usage_str
            return
        if auto and (added_model_list or added_field_list or initial):
            print "You cannot use --auto and other options together"
            print self.usage_str
            return
        
        # specify the default name 'initial' if a name wasn't specified and we're
        # doing a migration for an entire app
        if not name and initial:
            name = 'initial'
        
        # if not name, there's an error
        if not name:
            print "You must name this migration"
            print self.usage_str
            return
        
        if not app:
            print "Please provide an app in which to create the migration."
            print self.usage_str
            return
        
        # Make sure the app is short form
        app = app.split(".")[-1]
        
        # See if the app exists
        app_models_module = models.get_app(app)
        if not app_models_module:
            print "App '%s' doesn't seem to exist, isn't in INSTALLED_APPS, or has no models." % app
            print self.usage_str
            return
        
        # If they've set SOUTH_AUTO_FREEZE_APP = True (or not set it - defaults to True)
        if not hasattr(settings, 'SOUTH_AUTO_FREEZE_APP') or settings.SOUTH_AUTO_FREEZE_APP:
            if freeze_list and app not in freeze_list:
                freeze_list += [app]
            else:
                freeze_list = [app]
        
        # Make the migrations directory if it's not there
        app_module_path = app_models_module.__name__.split('.')[0:-1]
        try:
            app_module = __import__('.'.join(app_module_path), {}, {}, [''])
        except ImportError:
            print "Couldn't find path to App '%s'." % app
            print self.usage_str
            return
            
        migrations_dir = os.path.join(
            os.path.dirname(app_module.__file__),
            "migrations",
        )
        
        # Make sure there's a migrations directory and __init__.py
        if not os.path.isdir(migrations_dir):
            print "Creating migrations directory at '%s'..." % migrations_dir
            os.mkdir(migrations_dir)
        init_path = os.path.join(migrations_dir, "__init__.py")
        if not os.path.isfile(init_path):
            # Touch the init py file
            print "Creating __init__.py in '%s'..." % migrations_dir
            open(init_path, "w").close()
        
        # See what filename is next in line. We assume they use numbers.
        migrations = migration.get_migration_names(migration.get_app(app))
        highest_number = 0
        for migration_name in migrations:
            try:
                number = int(migration_name.split("_")[0])
                highest_number = max(highest_number, number)
            except ValueError:
                pass
        
        # Make the new filename
        new_filename = "%04i%s_%s.py" % (
            highest_number + 1,
            "".join([random.choice(string.letters.lower()) for i in range(0)]), # Possible random stuff insertion
            name,
        )
        
        # Find the source file encoding, using PEP 0263's method
        encoding = None
        first_two_lines = inspect.getsourcelines(app_models_module)[0][:2]
        for line in first_two_lines:
            if re.search("coding[:=]\s*([-\w.]+)", line):
                encoding = line
        
        # Initialise forwards, backwards and models to blank things
        forwards = ""
        backwards = ""
        frozen_models = {} # Frozen models, used by the Fake ORM
        complete_apps = set() # Apps that are completely frozen - useable for diffing.
        
        # Sets of actions
        added_models = set()
        deleted_models = [] # Special: contains instances _not_ string keys
        added_fields = set()
        deleted_fields = [] # Similar to deleted_models
        changed_fields = [] # (mkey, fname, old_def, new_def)
        added_uniques = set() # (mkey, field_names)
        deleted_uniques = set() # (mkey, field_names)
        
        # --initial means 'add all models in this app'.
        if initial:
            for model in models.get_models(app_models_module):
                added_models.add("%s.%s" % (app, model._meta.object_name))
        
        # Added models might be 'model' or 'app.model'.
        for modelname in added_model_list:
            if "." in modelname:
                added_models.add(modelname)
            else:
                added_models.add("%s.%s" % (app, modelname))
        
        # Fields need translating from "model.field" to (app.model, field)
        for fielddef in added_field_list:
            try:
                modelname, fieldname = fielddef.split(".", 1)
            except ValueError:
                print "The field specification '%s' is not in modelname.fieldname format." % fielddef
            else:
                added_fields.add(("%s.%s" % (app, modelname), fieldname))
        
        # Add anything frozen (I almost called the dict Iceland...)
        if freeze_list:
            for item in freeze_list:
                if "." in item:
                    # It's a specific model
                    app_name, model_name = item.split(".", 1)
                    model = models.get_model(app_name, model_name)
                    if model is None:
                        print "Cannot find the model '%s' to freeze it." % item
                        print self.usage_str
                        return
                    frozen_models[model] = None
                else:
                    # Get everything in an app!
                    frozen_models.update(dict([(x, None) for x in models.get_models(models.get_app(item))]))
                    complete_apps.add(item.split(".")[-1])
            # For every model in the freeze list, add in frozen dependencies
            for model in list(frozen_models):
                frozen_models.update(model_dependencies(model))
        
        
        ### Automatic Detection ###
        if auto:
            # Get the last migration for this app
            last_models = None
            app_module = migration.Migrations.from_name(app)
            if app_module is None:
                print "You cannot use automatic detection on the first migration of an app. Try --initial instead."
            else:
                migrations = list(migration.get_migration_classes(app_module))
                if not migrations:
                    print "You cannot use automatic detection on the first migration of an app. Try --initial instead."
                else:
                    if hasattr(migrations[-1], "complete_apps") and \
                       app in migrations[-1].complete_apps:
                        last_models = migrations[-1].models
                        last_orm = migrations[-1].orm
                    else:
                        print "You cannot use automatic detection, since the previous migration does not have this whole app frozen.\nEither make migrations using '--freeze %s' or set 'SOUTH_AUTO_FREEZE_APP = True' in your settings.py." % app
            
            # Right, did we manage to get the last set of models?
            if last_models is None:
                print self.usage_str
                return
            
            new = dict([
                (model_key(model), prep_for_freeze(model))
                for model in models.get_models(app_models_module)
                if (
                    not getattr(model._meta, "proxy", False) and \
                    getattr(model._meta, "managed", True) and \
                    not getattr(model._meta, "abstract", False)
                )
            ])
            # And filter other apps out of the old
            old = dict([
                (key, fields)
                for key, fields in last_models.items()
                if key.split(".", 1)[0] == app
            ])
            am, dm, cm, af, df, cf, afu, dfu = models_diff(old, new)
            
            # For models that were there before and after, do a meta diff
            was_meta_change = False
            for mkey in cm:
                au, du = meta_diff(old[mkey].get("Meta", {}), new[mkey].get("Meta", {}))
                for entry in au:
                    added_uniques.add((mkey, entry))
                    was_meta_change = True
                for entry in du:
                    deleted_uniques.add((mkey, entry, last_orm[mkey]))
                    was_meta_change = True
            
            if not (am or dm or af or df or cf or afu or dfu or was_meta_change):
                print "Nothing seems to have changed."
                return
            
            # Add items to the todo lists
            added_models.update(am)
            added_fields.update(af)
            changed_fields.extend(cf)
            
            # Deleted models are from the past, and so we use instances instead.
            for mkey in dm:
                model = last_orm[mkey]
                fields = last_models[mkey]
                if "Meta" in fields:
                    del fields['Meta']
                deleted_models.append((model, fields, last_models))
            
            # For deleted fields, we tag the instance on the end too
            for mkey, fname in df:
                deleted_fields.append((
                    mkey,
                    fname,
                    last_orm[mkey]._meta.get_field_by_name(fname)[0],
                    last_models[mkey][fname],
                    last_models,
                ))
            
            # Uniques need merging
            added_uniques = added_uniques.union(afu)
            
            for mkey, entry in dfu:
                deleted_uniques.add((mkey, entry, last_orm[mkey]))
        
        
        ### Added model ###
        for mkey in added_models:
            
            print " + Added model '%s'" % (mkey,)
            
            model = model_unkey(mkey)
            
            # Add the model's dependencies to the frozens
            frozen_models.update(model_dependencies(model))
            # Get the field definitions
            fields = modelsinspector.get_model_fields(model)
            # Turn the (class, args, kwargs) format into a string
            fields = triples_to_defs(app, model, fields)
            # Make the code
            forwards += CREATE_TABLE_SNIPPET % (
                model._meta.object_name,
                model._meta.db_table,
                "\n            ".join(["('%s', orm[%r])," % (fname, mkey + ":" + fname) for fname, fdef in fields.items()]),
                model._meta.app_label,
                model._meta.object_name,
            )
            # And the backwards code
            backwards += DELETE_TABLE_SNIPPET % (
                model._meta.object_name, 
                model._meta.db_table
            )
            # Now add M2M fields to be done
            for field in model._meta.local_many_to_many:
                added_fields.add((mkey, field.attname))
            # And unique_togethers to be added
            for ut in model._meta.unique_together:
                added_uniques.add((mkey, tuple(ut)))
        
        
        ### Added fields ###
        for mkey, field_name in added_fields:
            
            # Get the model
            model = model_unkey(mkey)
            # Get the field
            try:
                field = model._meta.get_field(field_name)
            except FieldDoesNotExist:
                print "Model '%s' doesn't have a field '%s'" % (mkey, field_name)
                return
            
            # ManyToMany fields need special attention.
            if isinstance(field, models.ManyToManyField):
                if not field.rel.through: # Bug #120
                    # Add a frozen model for each side
                    frozen_models[model] = None
                    frozen_models[field.rel.to] = None
                    # And a field defn, that's actually a table creation
                    forwards += CREATE_M2MFIELD_SNIPPET % (
                        model._meta.object_name,
                        field.name,
                        field.m2m_db_table(),
                        field.m2m_column_name()[:-3], # strip off the '_id' at the end
                        poss_ormise(app, model, model._meta.object_name),
                        field.m2m_reverse_name()[:-3], # strip off the '_id' at the ned
                        poss_ormise(app, field.rel.to, field.rel.to._meta.object_name)
                        )
                    backwards += DELETE_M2MFIELD_SNIPPET % (
                        model._meta.object_name,
                        field.name,
                        field.m2m_db_table()
                    )
                    print " + Added M2M '%s.%s'" % (mkey, field_name)
                continue
            
            # GenericRelations need ignoring
            if isinstance(field, GenericRelation):
                continue
            
            print " + Added field '%s.%s'" % (mkey, field_name)
            
            # Add any dependencies
            frozen_models.update(field_dependencies(field))
            
            # Work out the definition
            triple = remove_useless_attributes(
                modelsinspector.get_model_fields(model)[field_name])
            
            field_definition = make_field_constructor(app, field, triple)
            
            forwards += CREATE_FIELD_SNIPPET % (
                model._meta.object_name,
                field.name,
                model._meta.db_table,
                field.name,
                "orm[%r]" % (mkey + ":" + field.name),
            )
            backwards += DELETE_FIELD_SNIPPET % (
                model._meta.object_name,
                field.name,
                model._meta.db_table,
                field.column,
            )
        
        
        ### Deleted fields ###
        for mkey, field_name, field, triple, last_models in deleted_fields:
            
            print " - Deleted field '%s.%s'" % (mkey, field_name)
            
            # Get the model
            model = model_unkey(mkey)
            
            # ManyToMany fields need special attention.
            if isinstance(field, models.ManyToManyField):
                # And a field defn, that's actually a table deletion
                forwards += DELETE_M2MFIELD_SNIPPET % (
                    model._meta.object_name,
                    field.name,
                    field.m2m_db_table()
                )
                backwards += CREATE_M2MFIELD_SNIPPET % (
                    model._meta.object_name,
                    field.name,
                    field.m2m_db_table(),
                    field.m2m_column_name()[:-3], # strip off the '_id' at the end
                    poss_ormise(app, model, model._meta.object_name),
                    field.m2m_reverse_name()[:-3], # strip off the '_id' at the ned
                    poss_ormise(app, field.rel.to, field.rel.to._meta.object_name)
                    )
                continue
            
            # Work out the definition
            triple = remove_useless_attributes(triple)
            field_definition = make_field_constructor(app, field, triple)
            
            forwards += DELETE_FIELD_SNIPPET % (
                model._meta.object_name,
                field.name,
                model._meta.db_table,
                field.column,
            )
            backwards += CREATE_FIELD_SNIPPET % (
                model._meta.object_name,
                field.name,
                model._meta.db_table,
                field.name,
                "orm[%r]" % (mkey + ":" + field.name),
            )
        
        
        ### Deleted model ###
        for model, fields, last_models in deleted_models:
            
            print " - Deleted model '%s.%s'" % (model._meta.app_label,model._meta.object_name)
            
            # Turn the (class, args, kwargs) format into a string
            fields = triples_to_defs(app, model, fields)
            
            # Make the code
            forwards += DELETE_TABLE_SNIPPET % (
                model._meta.object_name, 
                model._meta.db_table
            )
            # And the backwards code
            backwards += CREATE_TABLE_SNIPPET % (
                model._meta.object_name,
                model._meta.db_table,
                "\n            ".join(["('%s', orm[%r])," % (fname, mkey + ":" + fname) for fname, fdef in fields.items()]),
                model._meta.app_label,
                model._meta.object_name,
            )
        
        
        ### Changed fields ###
        for mkey, field_name, old_triple, new_triple in changed_fields:
            
            model = model_unkey(mkey)
            old_def = triples_to_defs(app, model, {
                field_name: old_triple,
            })[field_name]
            new_def = triples_to_defs(app, model, {
                field_name: new_triple,
            })[field_name]
            
            # We need to create the field, to see if it needs _id, or if it's an M2M
            field = model._meta.get_field_by_name(field_name)[0]
            
            if hasattr(field, "m2m_db_table"):
                # See if anything has ACTUALLY changed
                if old_triple[1] != new_triple[1]:
                    print " ! Detected change to the target model of M2M field '%s.%s'. South can't handle this; leaving this change out." % (mkey, field_name)
                continue
            
            print " ~ Changed field '%s.%s'." % (mkey, field_name)
            
            forwards += CHANGE_FIELD_SNIPPET % (
                model._meta.object_name,
                field_name,
                new_def,
                model._meta.db_table,
                field.get_attname(),
                "orm[%r]" % (mkey + ":" + field.name),
            )
            
            backwards += CHANGE_FIELD_SNIPPET % (
                model._meta.object_name,
                field_name,
                old_def,
                model._meta.db_table,
                field.get_attname(),
                "orm[%r]" % (mkey + ":" + field.name),
            )
        
        
        ### Added unique_togethers ###
        for mkey, ut in added_uniques:
            
            model = model_unkey(mkey)
            if len(ut) == 1:
                print " + Added unique for %s on %s." % (", ".join(ut), model._meta.object_name)
            else:
                print " + Added unique_together for [%s] on %s." % (", ".join(ut), model._meta.object_name)
            
            cols = [get_field_column(model, f) for f in ut]
            
            forwards += CREATE_UNIQUE_SNIPPET % (
                ", ".join(ut),
                model._meta.object_name,
                model._meta.db_table,
                cols,
            )
            
            backwards = DELETE_UNIQUE_SNIPPET % (
                ", ".join(ut),
                model._meta.object_name,
                model._meta.db_table,
                cols,
            ) + backwards
        
        
        ### Deleted unique_togethers ###
        for mkey, ut, model in deleted_uniques:
            
            if len(ut) == 1:
                print " - Deleted unique for %s on %s." % (", ".join(ut), model._meta.object_name)
            else:
                print " - Deleted unique_together for [%s] on %s." % (", ".join(ut), model._meta.object_name)
            
            cols = [get_field_column(model, f) for f in ut]
            
            forwards = DELETE_UNIQUE_SNIPPET % (
                ", ".join(ut),
                model._meta.object_name,
                model._meta.db_table,
                cols,
            ) + forwards
            
            backwards += CREATE_UNIQUE_SNIPPET % (
                ", ".join(ut),
                model._meta.object_name,
                model._meta.db_table,
                cols,
            )
        
        
        # Default values for forwards/backwards
        if (not forwards) and (not backwards):
            forwards = '"Write your forwards migration here"'
            backwards = '"Write your backwards migration here"'
        
        all_models = {}
        
        # Fill out frozen model definitions
        for model, last_models in frozen_models.items():
            all_models[model_key(model)] = prep_for_freeze(model, last_models)
        
        # Do some model cleanup, and warnings
        for modelname, model in all_models.items():
            for fieldname, fielddef in model.items():
                # Remove empty-after-cleaning Metas.
                if fieldname == "Meta" and not fielddef:
                    del model['Meta']
                # Warn about undefined fields
                elif fielddef is None:
                    print "WARNING: Cannot get definition for '%s' on '%s'. Please edit the migration manually to define it, or add the south_field_triple method to it." % (
                        fieldname,
                        modelname,
                    )
                    model[fieldname] = FIELD_NEEDS_DEF_SNIPPET
        
        # So, what's in this file, then?
        file_contents = MIGRATION_SNIPPET % (
            encoding or "", '.'.join(app_module_path), 
            forwards, 
            backwards, 
            pprint_frozen_models(all_models),
            complete_apps and "complete_apps = [%s]" % (", ".join(map(repr, complete_apps))) or ""
        )
        # - is a special name which means 'print to stdout'
        if name == "-":
            print file_contents
        # Write the migration file if the name isn't -
        else:
            fp = open(os.path.join(migrations_dir, new_filename), "w")
            fp.write(file_contents)
            fp.close()
            print "Created %s." % new_filename


### Cleaning functions for freezing


def ormise_triple(field, triple):
    "Given a 'triple' definition, runs poss_ormise on each arg."
    
    # If it's a string defn, return it plain.
    if not isinstance(triple, (list, tuple)):
        return triple
    
    # For each arg, if it's a related type, try ORMising it.
    args = []
    for arg in triple[1]:
        if hasattr(field, "rel") and hasattr(field.rel, "to") and field.rel.to:
            args.append(poss_ormise(None, field.rel.to, arg))
        else:
            args.append(arg)
    
    return (triple[0], args, triple[2])


def prep_for_freeze(model, last_models=None):
    # If we have a set of models to use, use them.
    if last_models:
        fields = last_models[model_key(model)]
    else:
        fields = modelsinspector.get_model_fields(model, m2m=True)
    # Remove _stub if it stuck in
    if "_stub" in fields:
        del fields["_stub"]
    # Remove useless attributes (like 'choices')
    for name, field in fields.items():
        if name == "Meta":
            continue
        real_field = model._meta.get_field_by_name(name)[0]
        fields[name] = ormise_triple(real_field, remove_useless_attributes(field))
    # See if there's a Meta
    if last_models:
        meta = last_models[model_key(model)].get("Meta", {})
    else:
        meta = modelsinspector.get_model_meta(model)
    if meta:
        fields['Meta'] = remove_useless_meta(meta)
    return fields


### Module handling functions

def model_key(model):
    "For a given model, return 'appname.modelname'."
    return "%s.%s" % (model._meta.app_label, model._meta.object_name.lower())

def model_unkey(key):
    "For 'appname.modelname', return the model."
    app, modelname = key.split(".", 1)
    model = models.get_model(app, modelname)
    if not model:
        print "Couldn't find model '%s' in app '%s'" % (modelname, app)
        sys.exit(1)
    return model

### Dependency resolvers

def model_dependencies(model, last_models=None, checked_models=None):
    """
    Returns a set of models this one depends on to be defined; things like
    OneToOneFields as ID, ForeignKeys everywhere, etc.
    """
    depends = {}
    checked_models = checked_models or set()
    # Get deps for each field
    for field in model._meta.fields + model._meta.many_to_many:
        depends.update(field_dependencies(field, last_models))
    # Now recurse
    new_to_check = set(depends.keys()) - checked_models
    while new_to_check:
        checked_model = new_to_check.pop()
        if checked_model == model or checked_model in checked_models:
            continue
        checked_models.add(checked_model)
        deps = model_dependencies(checked_model, last_models, checked_models)
        # Loop through dependencies...
        for dep, value in deps.items():
            # If the new dep is not already checked, add to the queue
            if (dep not in depends) and (dep not in new_to_check) and (dep not in checked_models):
                new_to_check.add(dep)
            depends[dep] = value
    return depends


def field_dependencies(field, last_models=None, checked_models=None):
    checked_models = checked_models or set()
    depends = {}
    if isinstance(field, (models.OneToOneField, models.ForeignKey, models.ManyToManyField, GenericRelation)):
        if field.rel.to in checked_models:
            return depends
        checked_models.add(field.rel.to)
        depends[field.rel.to] = last_models
        depends.update(field_dependencies(field.rel.to._meta.pk, last_models, checked_models))
    return depends
    


### Prettyprinters

def pprint_frozen_models(models):
    return "{\n        %s\n    }" % ",\n        ".join([
        "%r: %s" % (name, pprint_fields(fields))
        for name, fields in sorted(models.items())
    ])

def pprint_fields(fields):
    return "{\n            %s\n        }" % ",\n            ".join([
        "%r: %r" % (name, defn)
        for name, defn in sorted(fields.items())
    ])


### Output sanitisers


USELESS_KEYWORDS = ["choices", "help_text", "upload_to", "verbose_name"]
USELESS_DB_KEYWORDS = ["related_name"] # Important for ORM, not for DB.

def remove_useless_attributes(field, db=False):
    "Removes useless (for database) attributes from the field's defn."
    keywords = db and USELESS_DB_KEYWORDS or USELESS_KEYWORDS
    if field:
        for name in keywords:
            if name in field[2]:
                del field[2][name]
    return field

USELESS_META = ["verbose_name", "verbose_name_plural"]
def remove_useless_meta(meta):
    "Removes useless (for database) attributes from the table's meta."
    if meta:
        for name in USELESS_META:
            if name in meta:
                del meta[name]
    return meta


### Turns (class, args, kwargs) triples into function defs.

def make_field_constructor(default_app, field, triple):
    """
    Given the defualt app, the field class,
    and the defn triple (or string), make the definition string.
    """
    # It might be None; return a placeholder
    if triple is None:
        return FIELD_NEEDS_DEF_SNIPPET
    # It might be a defn string already...
    if isinstance(triple, (str, unicode)):
        return triple
    # OK, do it the hard way
    if hasattr(field, "rel") and hasattr(field.rel, "to") and field.rel.to:
        rel_to = field.rel.to
    else:
        rel_to = None
    args = [poss_ormise(default_app, rel_to, arg) for arg in triple[1]]
    kwds = ["%s=%s" % (k, poss_ormise(default_app, rel_to, v)) for k,v in triple[2].items()]
    return "%s(%s)" % (triple[0], ", ".join(args+kwds))

QUOTES = ['"""', "'''", '"', "'"]

def poss_ormise(default_app, rel_to, arg):
    """
    Given the name of something that needs orm. stuck on the front and
    a python eval-able string, possibly add orm. to it.
    """
    orig_arg = arg
    # If it's not a relative field, short-circuit out
    if not rel_to:
        return arg
    # Get the name of the other model
    rel_name = rel_to._meta.object_name
    # Is it in a different app? If so, use proper addressing.
    if rel_to._meta.app_label != default_app:
        real_name = "orm['%s.%s']" % (rel_to._meta.app_label, rel_name)
    else:
        real_name = "orm.%s" % rel_name
    # If it's surrounded by quotes, get rid of those
    for quote_type in QUOTES:
        l = len(quote_type)
        if arg[:l] == quote_type and arg[-l:] == quote_type:
            arg = arg[l:-l]
            break
    # Now see if we can replace it.
    if arg.lower() == rel_name.lower():
        return real_name
    # Or perhaps it's app.model?
    if arg.lower() == rel_to._meta.app_label.lower() + "." + rel_name.lower():
        return real_name
    # Or perhaps it's 'self'?
    if arg == RECURSIVE_RELATIONSHIP_CONSTANT:
        return real_name
    return orig_arg


### Diffing functions between sets of models

def models_diff(old, new):
    """
    Returns the difference between the old and new sets of models as a 5-tuple:
    added_models, deleted_models, added_fields, deleted_fields, changed_fields
    """
    
    added_models = set()
    deleted_models = set()
    ignored_models = set() # Stubs for backwards
    continued_models = set() # Models that existed before and after
    added_fields = set()
    deleted_fields = set()
    changed_fields = []
    added_uniques = set()
    deleted_uniques = set()
    
    # See if anything's vanished
    for key in old:
        if key not in new:
            if "_stub" not in old[key]:
                deleted_models.add(key)
            else:
                ignored_models.add(key)
    
    # Or appeared
    for key in new:
        if key not in old:
            added_models.add(key)
    
    # Now, for every model that's stayed the same, check its fields.
    for key in old:
        if key not in deleted_models and key not in ignored_models:
            continued_models.add(key)
            still_there = set()
            # Find fields that have vanished.
            for fieldname in old[key]:
                if fieldname != "Meta" and fieldname not in new[key]:
                    deleted_fields.add((key, fieldname))
                else:
                    still_there.add(fieldname)
            # And ones that have appeared
            for fieldname in new[key]:
                if fieldname != "Meta" and fieldname not in old[key]:
                    added_fields.add((key, fieldname))
            # For the ones that exist in both models, see if they were changed
            for fieldname in still_there:
                if fieldname != "Meta":
                    if different_attributes(
                     remove_useless_attributes(old[key][fieldname], True),
                     remove_useless_attributes(new[key][fieldname], True)):
                        changed_fields.append((key, fieldname, old[key][fieldname], new[key][fieldname]))
                    # See if their uniques have changed
                    old_triple = old[key][fieldname]
                    new_triple = new[key][fieldname]
                    if is_triple(old_triple) and is_triple(new_triple):
                        if old_triple[2].get("unique", "False") != new_triple[2].get("unique", "False"):
                            # Make sure we look at the one explicitly given to see what happened
                            if "unique" in old_triple[2]:
                                if old_triple[2]['unique'] == "False":
                                    added_uniques.add((key, (fieldname,)))
                                else:
                                    deleted_uniques.add((key, (fieldname,)))
                            else:
                                if new_triple[2]['unique'] == "False":
                                    deleted_uniques.add((key, (fieldname,)))
                                else:
                                    added_uniques.add((key, (fieldname,)))
    
    return added_models, deleted_models, continued_models, added_fields, deleted_fields, changed_fields, added_uniques, deleted_uniques


def is_triple(triple):
    "Returns whether the argument is a triple."
    return isinstance(triple, (list, tuple)) and len(triple) == 3 and \
        isinstance(triple[0], (str, unicode)) and \
        isinstance(triple[1], (list, tuple)) and \
        isinstance(triple[2], dict)


def different_attributes(old, new):
    """
    Backwards-compat comparison that ignores orm. on the RHS and not the left
    and which knows django.db.models.fields.CharField = models.CharField.
    Has a whole load of tests in tests/autodetectoion.py.
    """
    
    # If they're not triples, just do normal comparison
    if not is_triple(old) or not is_triple(new):
        return old != new
    
    # Expand them out into parts
    old_field, old_pos, old_kwd = old
    new_field, new_pos, new_kwd = new
    
    # Copy the positional and keyword arguments so we can compare them and pop off things
    old_pos, new_pos = old_pos[:], new_pos[:]
    old_kwd = dict(old_kwd.items())
    new_kwd = dict(new_kwd.items())
    
    # Remove comparison of the existence of 'unique', that's done elsewhere.
    # TODO: Make this work for custom fields where unique= means something else?
    if "unique" in old_kwd:
        del old_kwd['unique']
    if "unique" in new_kwd:
        del new_kwd['unique']
    
    # If the first bit is different, check it's not by dj.db.models...
    if old_field != new_field:
        if old_field.startswith("models.") and (new_field.startswith("django.db.models") \
         or new_field.startswith("django.contrib.gis")):
            if old_field.split(".")[-1] != new_field.split(".")[-1]:
                return True
            else:
                # Remove those fields from the final comparison
                old_field = new_field = ""
    
    # If there's a positional argument in the first, and a 'to' in the second,
    # see if they're actually comparable.
    if (old_pos and "to" in new_kwd) and ("orm" in new_kwd['to'] and "orm" not in old_pos[0]):
        # Do special comparison to fix #153
        try:
            if old_pos[0] != new_kwd['to'].split("'")[1].split(".")[1]:
                return True
        except IndexError:
            pass # Fall back to next comparison
        # Remove those attrs from the final comparison
        old_pos = old_pos[1:]
        del new_kwd['to']
    
    return old_field != new_field or old_pos != new_pos or old_kwd != new_kwd
    
    


def meta_diff(old, new):
    """
    Diffs the two provided Meta definitions (dicts).
    """
    
    # First, diff unique_together
    old_unique_together = eval(old.get('unique_together', "[]"))
    new_unique_together = eval(new.get('unique_together', "[]"))
    
    added_uniques = set()
    removed_uniques = set()
    
    for entry in old_unique_together:
        if entry not in new_unique_together:
            removed_uniques.add(tuple(entry))
    
    for entry in new_unique_together:
        if entry not in old_unique_together:
            added_uniques.add(tuple(entry))
    
    return added_uniques, removed_uniques


### Used to work out what columns any fields affect ###

def get_field_column(model, field_name):
    return model._meta.get_field_by_name(field_name)[0].column


### Creates SQL snippets for various common operations


def triples_to_defs(app, model, fields):
    # Turn the (class, args, kwargs) format into a string
    for field, triple in fields.items():
        triple = remove_useless_attributes(triple)
        if triple is None:
            print "WARNING: Cannot get definition for '%s' on '%s'. Please edit the migration manually." % (
                field,
                model_key(model),
            )
            fields[field] = FIELD_NEEDS_DEF_SNIPPET
        else:
            fields[field] = make_field_constructor(
                app,
                model._meta.get_field_by_name(field)[0],
                triple,
            )
    return fields


### Various code snippets we need to use

MIGRATION_SNIPPET = """%s
from south.db import db
from django.db import models
from %s.models import *

class Migration:
    
    def forwards(self, orm):
        %s
    
    
    def backwards(self, orm):
        %s
    
    
    models = %s
    
    %s
"""
CREATE_TABLE_SNIPPET = '''
        # Adding model '%s'
        db.create_table(%r, (
            %s
        ))
        db.send_create_signal(%r, [%r])
        '''
DELETE_TABLE_SNIPPET = '''
        # Deleting model '%s'
        db.delete_table(%r)
        '''
CREATE_FIELD_SNIPPET = '''
        # Adding field '%s.%s'
        db.add_column(%r, %r, %s)
        '''
DELETE_FIELD_SNIPPET = '''
        # Deleting field '%s.%s'
        db.delete_column(%r, %r)
        '''
CHANGE_FIELD_SNIPPET = '''
        # Changing field '%s.%s'
        # (to signature: %s)
        db.alter_column(%r, %r, %s)
        '''
CREATE_M2MFIELD_SNIPPET = '''
        # Adding ManyToManyField '%s.%s'
        db.create_table('%s', (
            ('id', models.AutoField(verbose_name='ID', primary_key=True, auto_created=True)),
            ('%s', models.ForeignKey(%s, null=False)),
            ('%s', models.ForeignKey(%s, null=False))
        ))
        '''
DELETE_M2MFIELD_SNIPPET = '''
        # Dropping ManyToManyField '%s.%s'
        db.delete_table('%s')
        '''
CREATE_UNIQUE_SNIPPET = '''
        # Creating unique_together for [%s] on %s.
        db.create_unique(%r, %r)
        '''
DELETE_UNIQUE_SNIPPET = '''
        # Deleting unique_together for [%s] on %s.
        db.delete_unique(%r, %r)
        '''
FIELD_NEEDS_DEF_SNIPPET = "<< PUT FIELD DEFINITION HERE >>"