PostGIS database to be queried by GeoDjango

Question

I would like to create a PostgreSQL database (postgreslq-9.1 and postgis-2.0.2) storing several shapefiles but I am uncertain on how to implement it.

I have already done this last year but was pretty uncomfortable beacause I had a table per shapefile, every table signed with its SRID (stored inside geometry_columns table - I was using postgis 1.5, so this was still a table and not a view as in postgis-2).

I had to create a new table every time I converted a shapefile: pretty uncomfortable because I had to query them using Django ORM, and create table mapping on the fly is not trivial.

Is that possible to create one single table having an id indicating the original shapefile and the relative SRID per geometry?

Answer 1

After some experiments, I think I've found in django-mutant the solution that fit my needs. With it, you can create a dynamic model in the following way:

from mutant.contrib.geo.models import GeoModel, GeometryFieldDefinition
from mutant.contrib.numeric.models import SmallIntegerFieldDefinition
from mutant.models import BaseDefinition, ModelDefinition

model_def, created = ModelDefinition.objects.get_or_create(
                         app_label='myApp',
                         object_name='myShape',
                         defaults=dict(
                         bases=(BaseDefinition(base=GeoModel),),
                         fields=(GeometryFieldDefinition(name='the_geom', srid=31258),
                         SmallIntegerFieldDefinition(name='cat'),)
                    )
                )

In this way, calling model_def.model_class() would return the same model as if you had declared the following in your models.py:

class myShape(GeoModel):
    cat = models.SmallIntegerField()
    the_geom = models.GeometryField(srid=31258)
    class Meta:
        db_table = u'myApp'

As you run ModelDefinition.objects.get_or_create() method, a table named mutant_myApp_myShape is created into PostgreSQL with a relative row in geometry_colums table. In addition, this model has a proper id entry inside django-mutant table named mutant_modeldefinition.

Further tests need to be made, but this approach seems a good starting point to me.

Answer 2

Try using shp2pgsql to load your Shapefiles into PostGIS. This command-line utility comes free with PostGIS. This article describes how to load Shapefiles in batch on Windows. The utility also has a switch, -a, that will allow you to append the Shapefile to an existing table, rather than creating a new one, provided that the table and the Shapefile share the same schema. From the shp2pgsql man page:

OPTIONS
    The loader has several operating modes distinguished by command line flags:

    (Note that -a, -c, -d and -p are mutually exclusive.)

    -a     Appends data from the Shape file into the database table. Note that to use this option to load multiple files, the files must have the same attributes and same data types.