As the question asks, is it necessary to have a numeric (and presumably, integer) value for a model's id? Or is any unique identifier acceptable? For example, could I use a GUID string?
It can be any arbitrary string according to the docs:
ID
A special property of models, the id is an arbitrary string (integer
id or UUID). If you set the id in the attributes hash, it will be
copied onto the model as a direct property. Models can be retrieved by
id from collections, and the id is used to generate model URLs by
default.
Yes you can. The backbone documentation states that "the id is an arbitrary string (integer id or UUID)".
Related
In my database model, my attribute is set as type INT.
On the front end, I want to display a select field with representative values for the respective Integer values.
eg: [1 = Home, 2 = About]
I am currently using an external plugin for the administrating content, and the select values only allows integer. So my idea is to achieve this at respective Model. Is it possible?
Genarally yes.
You should be able to attach results of Model->find('list') to select field. Of course your model should have name or title fields for description values (Home, About).
Sounds like the kind of enum representation as I always use.
Try this solution:
http://www.dereuromark.de/2010/06/24/static-enums-or-semihardcoded-attributes/
I basically uses an array matching to resolve those ints into strings in a clean way - using the model. can be the whole array for select fields or just the specific string for output in the view/index.
Its also fully form and bake-template capable.
If you name the field "attribute" in your table, and name the method "attributes()" you can easily have "cake bake" to bake this via custom templates.
I see the document
https://developers.google.com/appengine/docs/python/ndb/keyclass#Key_integer_id
Returns the integer id in the last (kind, id) pair, or None if the key
has an string id or is incomplete.
see I think the id of a key can be a int ; so I write
r = ndb.Key(UserSession, int(id)).get()
if r:
return r.session
but the dev_server.py , will always raise
File "/home/bitcoin/down/google_appengine/google/appengine/datastore/datastore_stub_util.py", line 346, in CheckReference
raise datastore_errors.BadRequestError('missing key id/name')
BadRequestError: missing key id/name
I chanage the int(id) -> str(id)
seems right ;
so my question is , How to use ndb key with integer_id ?
the model is
class UserSession(ndb.Model):
session = ndb.BlobProperty()
The type of the id you use when reading the entity must match the type of the id you used when you wrote the entity. Normally, integer ids are assigned automatically when you write a new entity without specifying an id or key; you then get the id out of the key returned by entity.put(). It is generally not recommended to assign your own integer ids; when the app assigns the keys, the convention is that they should be strings.
There's an easier way to fetch:
UserSession.get_by_id(int(id))
https://developers.google.com/appengine/docs/python/ndb/modelclass#Model_get_by_id
If that doesn't work, I suspect that id is wrong or empty.
There must be something wrong with your variable 'id'.
Your code here should be no problem, and it's better to user long instead of int.
You can try your code on interactive console of development server with specific integer id.
It may be easier to identify your entities in the sessions with their keys instead of their ids. There really is no need to extract the ID from the key to identify the session (other than maybe saving a bit of memory. I think the way your thinking is based on a RDB. I learned that using the key actually makes entity/session identifications easier.
'id' is also a python builtin function. Maybe you are taking that by mistake.
I want to get an entity key knowing entity ID and an ancestor.
ID is unique within entity group defined by the ancestor.
It seems to me that it's not possible using ndb interface. As I understand datastore it may be caused by the fact that this operation requires full index scan to perform.
The workaround I used is to create a computed property in the model, which will contain the id part of the key. I'm able now to do an ancestor query and get the key
class SomeModel(ndb.Model):
ID = ndb.ComputedProperty( lambda self: self.key.id() )
#classmethod
def id_to_key(cls, identifier, ancestor):
return cls.query(cls.ID == identifier,
ancestor = ancestor.key ).get( keys_only = True)
It seems to work, but are there any better solutions to this problem?
Update
It seems that for datastore the natural solution is to use full paths instead of identifiers. Initially I thought it'd be too burdensome. After reading dragonx answer I redesigned my application. To my suprise everything looks much simpler now. Additional benefits are that my entities will use less space and I won't need additional indexes.
I ran into this problem too. I think you do have the solution.
The better solution would be to stop using IDs to reference entities, and store either the actual key or a full path.
Internally, I use keys instead of IDs.
On my rest API, I used to do http://url/kind/id (where id looked like "123") to fetch an entity. I modified that to provide the complete ancestor path to the entity: http://url/kind/ancestor-ancestor-id (789-456-123), I'd then parse that string, generate a key, and then get by key.
Since you have full information about your ancestor and you know your id, you could directly create your key and get the entity, as follows:
my_key = ndb.Key(Ancestor, ancestor.key.id(), SomeModel, id)
entity = my_key.get()
This way you avoid making a query that costs more than a get operation both in terms of money and speed.
Hope this helps.
I want to make a little addition to dargonx's answer.
In my application on front-end I use string representation of keys:
str(instance.key())
When I need to make some changes with instence even if it is a descendant I use only string representation of its key. For example I have key_str -- argument from request to delete instance':
instance = Kind.get(key_str)
instance.delete()
My solution is using urlsafe to get item without worry about parent id:
pk = ndb.Key(Product, 1234)
usafe = LocationItem.get_by_id(5678, parent=pk).key.urlsafe()
# now can get by urlsafe
item = ndb.Key(urlsafe=usafe)
print item
I know how XWD_ID (xwikidoc) is created, but I don't know how XWO_ID (xwikiobject) is
created. I know that this is the same ID for tables xwikidates, xwikiintegers, xwikilargestrings,... But I don't know how it is created.
Can you help me ?
Thanks,
Caroline.
All IDs are assigned manually so far, and they are obtained from the entity's getId() method. For objects, this is BaseElement.getId() which is the new method of computing IDs (introduced in 4.0). Up to 3.5, it used to be BaseCollection.getId() which is actually the hashCode of the object, which is the hashcode of the string obtained by concatenating the document name, the XClass name, and the object number.
Quick Question. In the below code, you can see that the for loop (which takes all of the records in newTimecards and puts them as a variable called timecard) and adds the Resource_c to the resourceIds set. I'm confused about how this object is considered an ID data type. When an object is made in Salesforce does it automatically have an ID made, so that it knows Resource_c ID can be added to a set? Note that within the Resource_c Object there is also a field called Resource_ID_c. Resource_c within Timecard_c is a Master-Detail data type. Resource_c is the parent of Timecard_c.
Now that I think about it, resourceIds.add(timecard.Resource_c), does that reference the relationship between the two objects and then searches through Resource_c and adds the ID field Resource_ID_c automactically since it's a unique field?
Thanks for your help.
public class TimecardManager {
public class TimecardException extends Exception {}
public static void handleTimecardChange(List<Timecard__c> oldTimecards,
List<Timecard__c> newTimecards) {
Set<ID> resourceIds = new Set<ID>();
for (Timecard__c timecard : newTimecards) {
resourceIds.add(timecard.Resource__c);
}
Every object instance (and that means EVERY, including factory ones) has a unique organization level ID, whose field name is always Id, is covered by Apex type ID and is a case-sensitive string of 15 characters that also has an 18 character case-insensitive representation. The first three characters are object prefix code (e.g. 500 for a Case) so all instances of the same object share the same prefix. You see these values all across SF (for example in https://na1.salesforce.com/02s7000000BW59L the 02s7000000BW59L in the URL is the ID). When an instance of the object is created using INSERT DML operation, the salesforce automatically assigns unique value based on the prefix and the next available transactional sub ID, it all happens transparently to you.
This is not to be confused with object Name field which is a field you define when you create an object and which can be auto-incremented and so on (e.g. MYOBJ-{00000}) and which can have more meaning to a user than a cryptic ID
When you create a lookup or master-detail relationship it is ID that is being used to link the two instances, not the Name. In the above example Resource__c seems to be that lookup field and it contains Id value of row's master.
What the code does is it enumerates all resources used in timelines and builds a set of their IDs, the purpose of which is most probably to be used via WHERE Id IN :resourceIds clause to load resource details from master table.
mmix's answer is a great overview to what an ID is and where it comes from. To answer what I think is your specific question:
Any time there is a reference from one object to another (like here, between Timecard_c and Resource_c), the field representing the reference will be an ID. So, the for loop that calls resourceIds.add(timecard.Resource__c) is just building up your set of ID's (those 15-character strings). The timecard.Resource__c doesn't look through the Resource__c table to find the ID, timecard.Resource__c is the ID.