======================
``GeoJSON`` Serializer
======================

.. module:: django.contrib.gis.serializers.geojson
    :synopsis: Serialization of GeoDjango models in the GeoJSON format.

GeoDjango provides a specific serializer for the `GeoJSON`__ format. See
:doc:`/topics/serialization` for more information on serialization.

__ https://geojson.org/

The ``geojson`` serializer is not meant for round-tripping data, as it has no
deserializer equivalent. For example, you cannot use :djadmin:`loaddata` to
reload the output produced by this serializer. If you plan to reload the
outputted data, use the plain :ref:`json serializer <serialization-formats-json>`
instead.

In addition to the options of the ``json`` serializer, the ``geojson``
serializer accepts the following additional option when it is called by
``serializers.serialize()``:

* ``geometry_field``: A string containing the name of a geometry field to use
  for the ``geometry`` key of the GeoJSON feature. This is only needed when you
  have a model with more than one geometry field and you don't want to use the
  first defined geometry field (by default, the first geometry field is picked).

* ``id_field``: A string containing the name of a field to use for the ``id``
  key of the GeoJSON feature. By default, the primary key of objects is used.

* ``srid``: The SRID to use for the ``geometry`` content. Defaults to 4326
  (WGS 84).

The :ref:`fields <subset-of-fields>` option can be used to limit fields that
will be present in the ``properties`` key, as it works with all other
serializers.

Example::

    from django.core.serializers import serialize
    from my_app.models import City

    serialize("geojson", City.objects.all(), geometry_field="point", fields=["name"])

Would output::

    {
        "type": "FeatureCollection",
        "crs": {"type": "name", "properties": {"name": "EPSG:4326"}},
        "features": [
            {
                "type": "Feature",
                "id": 1,
                "geometry": {"type": "Point", "coordinates": [-87.650175, 41.850385]},
                "properties": {"name": "Chicago"},
            }
        ],
    }

When the ``fields`` parameter is not specified, the ``geojson`` serializer adds
a ``pk`` key to the ``properties`` dictionary with the primary key of the
object as the value.

.. versionchanged:: 4.2

    The ``id`` key for serialized features was added. Also, the ``id_field``
    option was added to the ``geojson`` serializer.
