How to Fix Django Error: Related Field got invalid lookup: icontains

This error typically relates to trying to add a field to your search_fields, but the field is not actually text—perhaps it’s a ManyToManyField or a ForeignKey.

Given the following, we want to be able to search our tags when we're in the Blog List View in the admin:

class Blog(models.Model):
    tags = models.ManyToManyField('blog.Tag', blank=True)
    ...

class Tag(models.Model):
    name = models.CharField(max_length=50)
    ...

...and right now your admin.py's search_fields looks like this:

class BlogAdmin(ApprovalAdmin):
    ...
    search_fields = (..., 'tags',)
    ...

Since the field 'tags' is a ManyToManyField, we can't do a text search on it, so we need to change that to include a text-based field that belongs to 'tags.' We'll change it to this:

class BlogAdmin(ApprovalAdmin):
    ...
    search_fields = (..., 'tags__name',)
    ...

Using the double-underscore, we're telling Django: grab the name field from the tags that were chosen on Blog instances and search them.

This should hopefully fix your error!