I'm fairly new to django web development. And I got an error whereby I try to change a 'post' under admin url - so localhost:8080/admin. I'm able to create it successfully but when I try to click the post that I had just added. I'm getting this error:
Exception Type: DatabaseError Exception Value: This query is not
supported by the database.
And this is the code that I know is 'messing' with this query:
#Post is an abstract class
class BlogPost(Post):
...
translators = models.ManyToManyField(Staff, related_name='translators')
photographers = models.ManyToManyField(Staff, related_name='photographers')
authors = models.ManyToManyField(Staff, related_name='authors')
...
To explain what is going on with this blog post - it can have multiple 'owners'/people that contributed to this post and thus the decision using ManyToManyField. And vice-versa with the 'Staff' member - the type of 'member' can have multiple ownership on multiple posts (Let me know if this logic doesn't make any sense because it does to me).
I'm using mongodb for the database, django 1.5.11 and I have installed djangotoolbox. I've tried the following solutions with adding a relationship to BlogPost as shown below:
Class Staff(Member):
...
staff_posts = models.ManyToManyField(BlogPost, related_name="staff_posts")
...
But I'm getting an error on 'cannot import BlogPost'. I tried figuring out the reason of this error and I don't think that I have a circular dependance - after checking all of the files, there's no circular dependance.
MongoDB (or mongoengine, which I'm guessing you're using) doesn't support joins, so the typical way to model many-to-many relations in a relational database has to be implemented some other way.
One way is to use a ReferenceField inside a ListField. It might look like this (not tested):
class BlogPost(Post):
authors = models.ListField(models.ReferenceField(Staff))
...
Also see these answers:
https://stackoverflow.com/a/18747306/98057
https://stackoverflow.com/a/25568877/98057
Just to put it out there, I'm not real familiar with MongoDB.
However, I don't believe you need to define a ManyToManyField on your Staff class. You already have a ManyToMany defined in your BlogPost, having it defined in one class file is all that is required. (At least for MySQL).
Related
I have foo an instance of the ember-data model thing. thing.js has the following property :
owner: DS.belongsTo('user')
If I have foo with an empty owner, how can I, with only foo and the 'owner' string, retrieve the value 'user' representing the model of the owner relation?
EDIT: I want to allow my select-relation component to works with relations where the name is different from the class name
It sounds like you have some work to do to finish setting up your relationships. Have a read through this page of the guides.
If the relationships are set up correctly, to get the associated user, you should be able to do foo.owner. This assumes that users are already present in the store. I recommend using the Ember Inspector browser plugin to debug the relationships.
This looks like a use case for typeForRelationship.
In your example you should be able to do something like
store.modelFor('thing').typeForRelationship('owner', store);
If you don't like that approach you can use the belongsTo reference API, where you use the meta data from the relationship to get the type
foo.belongsTo('owner').type
The only thing with that approach is that the type property may not be public API and possible (though unlikely) to change at some point.
It seems I can do the following :
this.get('model').get('_internalModel._relationships.initializedRelationships.'+this.get('relation')+'.relationshipMeta.type')
model being an instance and relation the string of the relation name, it correctly return the model of the relation.
EDIT : a better solution not using private API courtesy from the ember discord :
function getRelatedModelName(record, relationName){
let ParentModelClass = record.constructor;
let meta = get(ParentModelClass, 'relationshipsByName').get(relationName);
return meta.type;
}
I have a model that have a URLField field and I need to make a migration that turns this field into a foreign key, where the string is a unique field of the other object, and, if the object does not exist create it.
for example, turn this:
class Event_UserVisit(Event_Base):
dest_url = models.URLField(max_length=1000)
into this:
class Event_UserVisit(Event_Base):
dest_url = models.ForeignKey(Page)
I've never done a manual migration like this and didn't find any tutorial or instructions to do something like this.
obviously doing a naive migration return errors like this:
django.db.utils.ProgrammingError: column "source_url_id" cannot be cast automatically to type integer
what's the best approach to do it?
note: I need to do this on a production db with lots of data, so I can't have long down time and can't lose any data.
thanks! :)
I don't think you can do this at the ORM level in one go (unless someone corrects me) You would need create a new FK maybe dest_url2 run migrations, then write a script to migrate the data. Next,delete dest_url again run migrations. Then rename dest_url2 to dest_url Django will detect the name change here.
However, I don't understand why you are linking an FK ID on page to a field called dest_url. A PK in Page should not be a 1000 max URL! It has no order and would make indexing hard and slow down your app. It would make more sense do have...
class Event_UserVisit(Event_Base):
page = models.ForeignKey(Page, related_name='eventvisits')
The I assume Page looks something like this...
class Page(models.Model):
dest_url = models.URLField(max_length=1000)
I have some models using django-polymorphic-model
eg.
class Article(PolymorphicModel):
...
class Blog(Article):
tags = ...
class Story(Article):
publish = ...
Normally if I get all articles, I just do Article.objects.all(), however what if I want to get all articles that tags are empty? If I do Articles.objects.filter(tags__isnull=True) it will break because other models don't have this field, I would like to include Story entries too, do I really have to split into 2 different queries and combine again?
OK After some digging for the documentation through issues, here is how to do it
Articles.objects.filter(Blog___tags__isnull=True)
Hope you found an answer before.
Articles.objects.filter(Q(Blog___tags__isnull=True)|Q(Story__tags__isnull=True))
I've been using the built-in Django comments system which has been working great. On a particular page I need to list the latest X comments which I've just been fetching with:
latest_comments =
Comment.objects.filter(is_public=True, is_removed=False)
.order_by('submit_date').reverse()[:5]
However I've now introduced a Boolean field 'published' into the parent object of the comments, and I want to include that in the query above. I've tried using the content_type and object_pk fields but I'm not really getting anywhere. Normally you'd do something like:
Comment.objects.filter(blogPost__published=True)
But as it is not stored like that I am not sure how to proceed.
posts_ids = BlogPost.objects.filter(is_published=True).values_list('id', flat=True) #return [3,4,5,...]
ctype = ContentType.objects.get_for_model(BlogPost)
latest_comments = Comment.objects.filter(is_public=True, is_removed=False, content_type=ctype, content_object__in=posts_ids).order_by('-submit_date')[:5]
Comments use GenericForeignKey to store the relation to parent object. Because of the way generic relations work related lookups using __<field> syntax are not supported.
You can accomplish the desired behaviour using the 'in' lookup, however it'll require lot of comparisons when there'll be a lot of BlogPosts.
ids = BlogPost.objects.filter(published=True).values_list('id', flat=True) # Get list of ids, you would probably want to limit number of items returned here
content_type = ContentType.objects.get_for_model(BlogPost) # Becasue we filter only comments for BlogPost
latest_comments = Comment.objects.filter(content_type=content_type, object_pk__in=ids, is_public=True, is_removed=False, ).order_by('submit_date').reverse()[:5]
See the Comment model doc for the description of all fields.
You just cannot do that in one query. Comments use GenericForeignKey. Documentation says:
Due to the way GenericForeignKey is implemented, you cannot use such
fields directly with filters (filter() and exclude(), for example) via
the database API.
I'd like to have access to one my model field verbose_name.
I can get it by the field indice like this
model._meta._fields()[2].verbose_name
but I need to get it dynamically. Ideally it would be something like this
model._meta._fields()['location_x'].verbose_name
I've looked at a few things but I just can't find it.
For Django < 1.10:
model._meta.get_field_by_name('location_x')[0].verbose_name
model._meta.get_field('location_x').verbose_name
For Django 1.11 and 2.0:
MyModel._meta.get_field('my_field_name').verbose_name
More info in the Django doc
The selected answer gives a proxy object which might look as below.
<django.utils.functional.__proxy__ object at 0x{SomeMemoryLocation}>
If anyone is seeing the same, you can find the string for the verbose name in the title() member function of the proxy object.
model._meta.get_field_by_name(header)[0].verbose_name.title()
A better way to write this would be:
model._meta.get_field(header).verbose_name.title()
where header will be the name of the field you are interested in. i.e., 'location-x' in OPs context.
NOTE: Developers of Django also feel that using get_field is better and thus have depreciated get_field_by_name in Django 1.10. Thus I would suggest using get_field no matter what version of Django you use.
model._meta.get_field_by_name('location_x')[0].verbose_name
You can also use:
Model.location_x.field.verbose_name
Model being the class name. I tested this on my Animal model:
Animal.sale_price.field.verbose_name
Animal.sale_price returns a DeferredAttribute, which has several meta data, like the verbose_name
Note: I'm using Django 3.1.5
If you want to iterate on all the fields you need to get the field:
for f in BotUser._meta.get_fields():
if hasattr(f, 'verbose_name'):
print(f.verbose_name)
# select fields for bulk_update : exclude primary key and relational
fieldsfields_to_update = []
for field_to_update in Model._meta.get_fields():
if not field_to_update.many_to_many and not field_to_update.many_to_one and not field_to_update.one_to_many and not field_to_update.one_to_one and not field_to_update.primary_key and not field_to_update.is_relation :
fields_to_update = fields_to_update + [field_to_update.name]
Model.objects.bulk_update(models_to_update , fields_to_update)