Exposing complex fields

[robertpoziumschi]

Hi guys,

Is there any way to expose fields like ImageField (the url) or ManyToManyField (list of ids)?

I tried the following for ImageField but it didn't work:

• subclassed ImageField class and overridden value_from_object to return the ImageField.url field
• created a property (in the model that contains the ImageField) which returns the ImageField.url field

Thank you, Robert

[vdboor]

Hi @robertpoziumschi

It seems you've touched a unpolished spot there. We're currently not using value_from_object(), only getattr(model_instance, fieldname). I'm not that familiar with value_from_object(), should that be the preferred route?

Fortunately, the current field structure does allow you to override attribute retrieval.

from gisserver.features import FeatureField
from gisserver.types import XsdElement

class XsdImageElement(XsdElement):
    def get_value(self, instance):
        return getattr(instance, self.model_attribute)  # mimics current behavior
        return self.source.object_from_object(instance)  # would call your function

class FeatureImageField(FeatureField):
    xsd_element_class = XsdImageElement

Then you can use the FeatureImageField in the FeatureType definition directly.

feature = FeatureType(
    fields=[
       "id",
       "name",
       FeatureImageField("image"),
    ]
)

Seeing the complexity, I do think we should provide some shortcuts to simplify this (e.g. allow overriding xsd_element_classdirectly from thefield()` function)

[vdboor]

I've added 2 fixes in the master branch:

• No longer needing to override FeatureField too: 915da46dbd35009d825e6a29a1b7b3ec91a6888c
• The code now reads value_from_object(): 4e5084a1a79c681d3468745e95388babccbc04a0

So the example above becomes:

class XsdImageElement(XsdElement):
    def get_value(self, instance):
        return self.source.object_from_object(instance)

feature = FeatureType(
    fields=[
       "id",
       "name",
       field("image", xsd_class=XsdImageElement),
    ]
)

[robertpoziumschi]

Thank you very much!

[vdboor]

@robertpoziumschi FYI, version 1.2 has just been released with M2M field support too.