South & GeoDjango & Spatialite

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Douglas Goldstein

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Oct 26, 2014, 1:45:53 AM10/26/14
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I hope I've distilled this down to a simple enough example to tell whether I'm doing something wrong or I've uncovered a bug. I am using Django 1.6.6 and South 0.8.4 or 1.0 (tried both).

My model is as follows for the migration below:

class Zone(models.Model):
    name = models.CharField('Zone Name', max_length=1024)
    geo = models.PolygonField('Geo Data about Zone')
    objects = models.GeoManager()


My migration is as follows:

class Migration(SchemaMigration):

    def forwards(self, orm):

        # Adding field 'Zone.geo'
        db.add_column(u'mapping_zone', 'geo',
                      self.gf('django.contrib.gis.db.models.fields.PolygonField')(null=True),
                      keep_default=False)


If I run this migration as: ./manage.py migrate -v 3 mapping
I get the following output:

 > mapping:0002_auto__chg_field_zone_geo
   = SELECT AddGeometryColumn('mapping_zone', 'geo', 4326, 'POLYGON', 2, 0); []
   = SELECT CreateSpatialIndex('mapping_zone', 'geo'); []
   = CREATE TABLE "_south_new_mapping_zone" ("geo" None, "map_id" integer NOT NULL, "name" varchar(1024) NOT NULL) []
   = INSERT INTO "_south_new_mapping_zone" ("name", "map_id") SELECT "name", "map_id", FROM "mapping_zone"; []
   = DROP TABLE "mapping_zone"; []
   = ALTER TABLE "_south_new_mapping_zone" RENAME TO "mapping_zone"; []

   = CREATE INDEX "mapping_zone_51513134" ON "mapping_zone"("map_id"); []

The result is the new mapping_zone table is created incorrectly and doesn't have the field type set correctly and all the Spatialite fields are missing. It appears that I need to suppress the CREATE TABLE from occurring. The hack to make this happens appears to be to edit south/db/sqlite3.py in the add_column() method, the last line is a call to self._remake_table() which needs to be changed as follows:

        if field.__class__.__module__ == 'django.contrib.gis.db.models.fields':
            self._column_sql_for_create(table_name, name, field, False)
        else:
            self._remake_table(table_name, added={
                field.column: (self._column_sql_for_create(table_name, name, field, False), field_default)
            })


Now if I delete my database and start over and migrate again I get the following behavior:

 > mapping:0002_auto__chg_field_zone_geo
   = SELECT AddGeometryColumn('mapping_zone', 'geo', 4326, 'POLYGON', 2, 0); []
   = SELECT CreateSpatialIndex('mapping_zone', 'geo'); []
   = SELECT AddGeometryColumn('mapping_zone', 'geo', 4326, 'POLYGON', 2, 0); []
   = SELECT CreateSpatialIndex('mapping_zone', 'geo'); []


The double call doesn't seem to harm anything but not sure how to suppress it.

Any advice would be much appreciated.

Andrew Godwin

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Oct 26, 2014, 4:25:25 AM10/26/14
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Hi Douglas,

South does not have very good support for Spatialite at all; this is mostly likely a bug in South, but one that will (unfortunately) never be fixed, as South has been EOL'd.

Django 1.7 has better (i.e. actually tested) support for Spatialite and a whole lot of workarounds to make things sort of work - remember that Spatialite, much like SQLite, does not really support table mutation very much (though add column is one of the few things it can do natively). I would encourage you to use PostGIS unless you've got a real good reason for using Spatialite (i.e. you're doing embedded development).

Andrew

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