class Customer
embeds_many :addresses
#....
end
class Address
embedded_in :customer
belongs_to :region
#...
end
I don't care about ever finding all the embedded addresses that reference a region, but I want to be able to use the region= and region_id accessors that would be generated by belongs_to.
The documentation says both sides of the relationship must be defined UNLESS one of them is embedded, but when I leave out the Region-side association, I get:
NoMethodError: undefined method `[]' for nil:NilClass
from /[...]/accessors.rb:113:in `needs_no_database_query?'
this is wrong structure... the embedded documents cannot be referenced in any other model than the parent documents.
as the documentation says
Embedded 1-n:
One to many relationships where the children are embedded in the parent document.
Referneced 1-n:
One to many relationships where the children are stored in a separate collection from the parent document
so there is no way that an embedded doc ( stored as an attribute in some document ) to be referenced as a separate collection ( like the Referenced 1-n relations)..
you can look into altering the models definitions to suite your purposes...
take a look at this question which discuss the same problem
Related
I'm having issues. I want to use the nice ExtJS associations, but they're not working properly.
Issues:
no association showing in the model
no data showing up after load
What are the quirks to watch out for?
I recently went through a very painful learning curve with the ExtJS associations, and came across some useful articles, as well as my own gotchas. Here is the summary for those who run into the same pains.
Rules for HasMany Associations in ExtJS
Always put your Proxies in your Models, not your Stores, unless you
have a very good reason not to [1]
Always require your child models if
using them in hasMany relationships. [2]
Always use foreignKey if you want to load the children at will
Always use associationKey if you return the children in the same response as the parent
You can use both foreignKey and associationKey if you like
Always name your hasMany relationships
Always use fully qualified model names in your hasMany relationship
Consider giving the reader root a meaningful name (other than "data")
The child model does not need a belongsTo relationship for the hasMany to work
[1] The store will inherit its model's proxy, and you can always override it
[2] To make it easy, and avoid potential circular references, you can require them in app.js
http://extjs-tutorials.blogspot.com/2012/05/extjs-hasmany-relationships-rules.html
Rules for HasOne and BelongsTo Associations in ExtJS
Put the proxy in the model, unless you have a very good reason not to
Always use fully qualified model name
Always set the getterName
Always set the setterName
Always set the associationKey, if the foreign object is returned in the same response as this object
Always set the foreignKey, if you want to load the foreign object at will
Consider changing the instanceName to something shorter
The getter behaves differently depending on whether the foreign object is loaded
or not. If it's loaded, the foreign object is returned. Otherwise,
you need to pass in a callback to get it.
You should set the name property if you plan to override this association.
You do not need a belongsTo relationship for a hasMany to work
Set the primaryKey property if the id field of the parent model is not "id"
Sometimes you need to use uses or requires for the belongsTo association. Watch
out for circular references though.
Calling setter() function does
not seem to set the instance. Set object.belongsToInstance = obj if
calling the setter().
http://extjs-tutorials.blogspot.com/2012/05/extjs-belongsto-association-rules.html
Misc
If you're applying your data to a grid, make sure you call reconfigure() on the grid using the new store
Your "foreignKey" property will be applied as a local filter to the ExtJS store; if you see the data loading over the network, but
not showing in your grid, make sure your model has the foreignKey
value defined as a field, or the local filter will exclude the data
quiety. To test if this is the case, hook into the store's "load"
event and call store.clearFilters(), and see if your data shows up
I have one document embedded in another in Mongoid.
class A < B
include Mongoid::Document
embeds_one :shipping_address, class_name: 'Address'
I have, in my case, omitted the inverse relation:
class Address
# embedded_in :A
Why is it, that although the API works fine and completely as expected:
address = A.address
address.zip = 1234
a.changed? #true
address.save
a.changed? #false
The document is not actually saved?
If i return the embedded_in statement, the save actually works fine.
My understanding of the Mongoid source is not the best so don't kick me too hard mods.
I assume that Mongoid is similar to ActiveRecord in this regard. With ActiveRecord, defining a :has_many does not change the parent object but includes methods for accessing the child. belongs_to on the other hand pulls methods for managing foreign keys.
Looking at the source code for Mongoid it seems that persistence is called from the embedded class to the parent and not the other way around (source). Removing the embedded_in would remove the additional methods for inserting the child into the parent.
Feel free to correct me if I am way off :)
While you can gain a lot when you choose to embed documents in MongoDB, you do give up the ability to query everything outside of the context of the parent. If you want to be able to work with Address documents independently, outside of the context of the parent document, you should link documents with has_many instead of embedding with embeds_many. This comes with it's own set of pros and cons.
If you choose to embed documents, you do specify embedded_in in the model and you access the embedded documents like this:
a = A.new # Parent document
a.addresses # Embedded Address documents
( Documentation Reference )
I am trying to load an entity by key using the id it was assigned by the datastore but I don't see any api method to do this (using NDB). I thought I would be able to make a Key from an integer id and use key.get() to load the entity, but I don't see a way to make a key from just an id. I suspect I am missing something obvious here. How should I load an entity where I only know the id of it?
Another way: ndb.Key(YourModel, id).get().
YourModel.get_by_id() gets a model instance by id.
here the docs:
https://developers.google.com/appengine/docs/python/ndb/modelclass#Model_get_by_id
don't think you can't get an entity by id without knowing the kind because instances of different Model classes can have the same id/key_name
Models in NDB don't define their key type as part of the model. This is nifty in that you can have one given model type that is accessible through multiple different kinds of keys and parents, which makes them more flexible. But it's somewhat problematic because it isn't always clear what the key represents or where it comes from.
So in cases where there's only ever one kind of key for a given model (which is almost every model), I like to create a class method for generating that key, which adds a bit of semantic clarity:
class Book(ndb.Model):
title = ndb.StringProperty()
pages = ndb.IntegerProperty()
#classmethod
def make_key(cls, isbn):
return ndb.Key(cls, isbn)
b = Book.make_key('1234-5678').get()
Sure the added code is not strictly necessary, but it adds clarity and makes my models more long-term maintainable.
You can parse the id to key string:
key = ndb.Key(YourModel, id).urlsafe().
and then:
result = YourModel.query(YourModel.key== key).get().
I have a RecipeJDO that contains a List<IngredientJDO>. RecipeJDO "owns" the ingredients. This has been working well for me for several weeks. Now I'd like to introduce a new class "GroceryListJDO", that references the ingredients owned by various recipes.
When I try to persist a new GroceryListJDO I get the following:
javax.jdo.JDOException: Duplicate property name: ingredients_id_OWN
NestedThrowables:
org.datanucleus.exceptions.NucleusException: Duplicate property name: ingredients_id_OWN
javax.jdo.JDOException: Duplicate property name: ingredients_id_OWN
Seems like there is an issue of "ownership" of the ingredients between RecipeJDO and GroceryListJDO.
I could probably change GroceryListJDO to merely contain a List<String> that acts as a kind of foreign key to IngredientsJDO, but that kind of defeats the purpose of using ORM- I'd have to manually fetch and attach the ingredients in my DAO.
What is the best way to manage JDO collections that need to "attach" to multiple container JDO classes?
This is with JDO on Google App Engine, FWIW.
Apparently, this is known as an "unowned" relationship, and is not directly supported in GAE. The workaround is what I feared: only one JDO class can own the collection; any other JDOs that reference these objects must persist only Keys, and manage the fetching/saving of the referenced objects manually.
I want to ensure an object is unique, and to throw an error when a user tries to save it (e.g. via the admin) if not? By unique, I mean that some of the object's attributes might hold the same values as those of other objects, but they can't ALL be identical to another object's values.
If I'm not mistaken, I can do this like so:
class Animal(models.Model):
common_name = models.CharField(max_length=150)
latin_name = models.CharField(max_length=150)
class Meta:
unique_together = ("common_name", "latin_name")
But then each time I refactor the model (e.g. to add a new field, or to change the name of an existing field), I also have to edit the list of fields in the parenthesis assigned to unique_together. With a simple model, that's OK, but with a substantial one, it becomes a real hassle during refactoring.
How can I avoid having to repeat typing out the list of field names in the unique_together parenthesis? Is there some way to pass the list of the model's fields to a variable and to assign that variable to unique_together instead?
Refactoring models is a rather expensive thing to do:
You will need to change all code using your models since field names correspond to object properties
You will have to change your database manually since Django cannot do this for you (at least the version I used the last time when I worked with Django couldn't)
Therefore I think updating the list of unique field names in the model meta class is the least issue you should worry about.
EDIT: If you really want to do this and all of your fields must be "unique together", then the guy at freenode is right and you'll have to write a custom metaclass. This is quite complicated and errorprone, plus it might render your code incompatible to future releases of Django.
Django's ORM "magic" is controlled by the metaclass ModelBase (django.db.models.base.ModelBase) of the generic base class Model. This class is responsible to take your class definition with all fields and Meta information and construct the class you will be using in your code later.
Here is a recipe on how you could achieve your goal:
Subclass ModelBase to use your own metaclass.
Override the method __new__(cls, name, bases, dict)
Inspect dict to gather the Meta member (dict["Meta"]) as well as all field members
Set meta.unique_together based on the names of the fields you gathered.
Call the super implementation (ModelBase.__new__)
Use the custom metaclass for all your unique models using the magic member __metaclass__ = MyMetaclass (or derive an abstract base class extending Model and overriding the metaclass)