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django/contrib/gis/db/backends/postgis/schema.py

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from django.db.backends.postgresql.schema import DatabaseSchemaEditor


class PostGISSchemaEditor(DatabaseSchemaEditor):
    geom_index_type = 'GIST'
    geom_index_ops_nd = 'GIST_GEOMETRY_OPS_ND'
    rast_index_wrapper = 'ST_ConvexHull(%s)'

    sql_alter_column_to_3d = "ALTER COLUMN %(column)s TYPE %(type)s USING ST_Force3D(%(column)s)::%(type)s"
    sql_alter_column_to_2d = "ALTER COLUMN %(column)s TYPE %(type)s USING ST_Force2D(%(column)s)::%(type)s"

    def geo_quote_name(self, name):
        return self.connection.ops.geo_quote_name(name)

    def _field_should_be_indexed(self, model, field):
        if getattr(field, 'spatial_index', False):
            return True
        return super()._field_should_be_indexed(model, field)

    def _create_index_sql(self, model, fields, **kwargs):
        if len(fields) != 1 or not hasattr(fields[0], 'geodetic'):
            return super()._create_index_sql(model, fields, **kwargs)

        field = fields[0]
        field_column = self.quote_name(field.column)

        if field.geom_type == 'RASTER':
            # For raster fields, wrap index creation SQL statement with ST_ConvexHull.
            # Indexes on raster columns are based on the convex hull of the raster.
            field_column = self.rast_index_wrapper % field_column
        elif field.dim > 2 and not field.geography:
            # Use "nd" ops which are fast on multidimensional cases
            field_column = "%s %s" % (field_column, self.geom_index_ops_nd)

        return self.sql_create_index % {
            "name": self.quote_name('%s_%s_id' % (model._meta.db_table, field.column)),
            "table": self.quote_name(model._meta.db_table),
            "using": "USING %s" % self.geom_index_type,
            "columns": field_column,
            "extra": '',
            "condition": '',
        }

    def _alter_column_type_sql(self, table, old_field, new_field, new_type):
        """
        Special case when dimension changed.
        """
        if not hasattr(old_field, 'dim') or not hasattr(new_field, 'dim'):
            return super()._alter_column_type_sql(table, old_field, new_field, new_type)

        if old_field.dim == 2 and new_field.dim == 3:
            sql_alter = self.sql_alter_column_to_3d
        elif old_field.dim == 3 and new_field.dim == 2:
            sql_alter = self.sql_alter_column_to_2d
        else:
            sql_alter = self.sql_alter_column_type
        return (
            (
                sql_alter % {
                    "column": self.quote_name(new_field.column),
                    "type": new_type,
                },
                [],
            ),
            [],
        )