django-tables2: Adding a new custom column not found in model

Question

I have the following table:

class TaskTable(tables.Table):

    def render_foo(self):
        raise Exception()

    class Meta:
        model = Task
        fields = ['foo']

for the following model:

class Task(models.Model):
    priority = models.PositiveIntegerField()
    title = models.CharField(max_length=1024)
    content = models.TextField(null=True, blank=True)

According to the docs, render_foo won't be executed if it is considered an empty value.

My requirement is that foo is not found in the Model. How can I implement the column foo?

Answer 1

You have to pass an empty_values=() keyword argument to the column, to quote the docs:

render methods are only called if the value for a cell is determined to be not an empty value. When a value is inColumn.empty_values, a default value is rendered instead (both Column.render and Table.render_FOO are skipped).

In your case, the 'value' for your non-existing column is None, so if that value is in empty_values, the default value (- by default is rendered).

So in code, it could look like this:

class TaskTable(tables.Table):
    foo = tables.Column(empty_values=())

    def render_foo(self):
        raise Exception()

    class Meta:
        model = Task

relevant docs