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.
Related
I would like to avoid costly repeated data base queries in Anylogic. I have seen the following thread in Stack Overflow What is the fastest way to look up continuous data on Anylogic (Java, SQL) where a simple three step answer is provided but I'm not sure what the second point of the three actually means:
Save all rows as instances of that class at model start-up into a map - you can use Origin/Destination as the key (use Anylogic's Pair object) and the class instance as the value
I have created a class that takes as inputs the information from each column of my database. I would now like to save each row as an instance of that class - is there an easy way to do this? I may be missing something simple as I'm new to Anylogic.
I'm also unsure of how to create a mapping, if anyone could add more detail to point 2 above I'd be very grateful!
this is effectively the best advice, you created the class, which is a great step, but now, one element of that class, will be used as the key... for example the name... for instance if your class has firstName as one variable and lastName as another variable, you will use a string that is the concatenation of firstName and lastName as your key. Of course any key is fine, assuming that it is unique for all your table. Also an integer as an id is ok too.
create a collection of type LinkedHashMap
Create a class (you did that)
Your collection will take as the key a String (first + last name) and as the value of the elment the class...
now, when you read your database you will have something like this:
for(Tuple t : yourQueryResults){
YourClass yc=new YourClass(t.get(db.var1),t.get(db.var2));
String totalName=t.get(db.first_name)+"_"+t.get(db.last_name);
yourCollection.put(totalName,yc);
}
Now every time you want to find someone with the a name, for example "John Doe", instead of making a query, you will do
yourCollection.get("John_Doe").theVarYouWant;
if you use an id instead of the name, you can set an int as the key, and then you will just do yourCollection.get(theId).theVarYouWant
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
in an app i have an entity that contains a list of other entities (let's say an event holding a list of assigned employees)
using objectify - i need to find all the events a particular employee is assigned to.
is there a basic way to filter a query if it contains the parameter - kind of the opposite of the query in
... quick pseudocode
findAll(Employee employee) {
...
return ofy.query(Event.class).filter("employees.contains", employee).list();
}
any help would be greatly appreciated
i tried just doing filter("employees", employee) after seeing this http://groups.google.com/group/objectify-appengine/browse_thread/thread/77ba676192c08e20 - but unfortunately this returns me an empty list
currently i'm doing something really inefficient - going through each event, iterating through the employees and adding them to a new list if it contains the given employee just to have something that works - i know this is not right though
let me add one thing,
the above query is not actually what it is, i was just using that because i did not think this would make a difference.
The Employee and Events are in the same entity group with Business as a parent
the actual query i am using is the following
ofy.query(Event.class).ancestor(businessKey).filter("employees", employee).list();
unfortunately this is still returning an empty list - does having the ancestor(key) in there mess up the filter?
solution, the employees field was not indexed correctly.
I added the datastore-indexes file to create a composite index, but was testing originally on a value that I added before the employees field was indexed, this was something stupid i was doing - simply having an index on the "business" field and the "employees" field fixed everything. the datastore-indexes file did not appear to be necessary, after deleting it and trying again everything worked fine.
Generally, you do this one of two ways:
Put a property of Set<Key<Employee>> on the Event
or
Put a property of Set<Key<Event>> on the Employee
You could also create a relationship entity, but if you're just doing filtering on values with relatively low counts, usually it's easier to just put the set property on one entity or the other.
Then filter as you describe:
ofy.query(Event.class).filter("employees", employee).list()
or
ofy.query(Employee.class).filter("events", event).list()
The list property should hold a Keys to the target entity. If you pass in an entity to the filter() method, Objectify will understand that you want to filter by the key instead.
Example :
/***************************************************/
#Entity
#Cache
public class News {
#Id Long id;
String news ;
#Index List<Long> friend_list = new ArrayList<Long>();
// My friends who can see my news , exemele : friend_list.add(id_f1); friend_list.add(id_f2); friend_list.add(id_f3);
//To make an operation on "friend_list", it is obligatory to index it
}
/*************************************************/
public News(Long id_f){
List<Long> friend_id = new ArrayList<Long>();
friend_id.add(id_f);
Query<Nesw> query = ofy().load().type(News.class).filter("friend_list in",friend_id).limit(limit);
//To filter a list, just after the name of the field you want to filter, add "IN".
//here ==> .filter("friend_list in",friend_id);
// if friend_list contains "id_friend" ==> the query return value
.........
}
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.
I have a Model called Version that looks like this:
from google.appengine.ext import db
import piece
class Version(db.Model):
"A particular version of a piece of writing."
parent_piece = db.ReferenceProperty(piece.Piece, collection_name='versions')
"The Piece to which this version belongs."
note = db.TextProperty()
"A note from the Author about this version."
content = db.TextProperty()
"The actual content of this version of the Piece."
published_on = db.DateProperty(auto_now_add=True)
"The date on which the version was published."
I would like to access instances of Version via their IDs, using Version.get_by_id(), but this call always returns None. I can see in the Datastore Viewer that they have ID values, and in the debugger, I can query for them but not use them:
>>> for each_ver in version.Version.all():
... print each_ver.key().id()
...
34
35
36
31
32
>>> a = version.Version.get_by_id(34)
>>> type(a)
<type 'NoneType'>
I see that there are plenty of questions here where people are able to use get_by_id() effectively just as I wish, and they do not see the results that I am seeing.
Could the problem be that each Version instance is a child in an Entity Group rather than a root of an Entity Group? Each Version lives in an Entity Group that looks like Member->Piece->Version. If that is the problem, is there a way that I can refer to Version entity without using its entire key? If that is not the problem, can anyone tell me what I can do to make get_by_id() work as expected?
Could the problem be that each Version
instance is a child in an Entity Group
rather than a root of an Entity Group?
Yes. An entity's key includes the keys of any parent entities.
If that is the problem, is there a
way that I can refer to Version entity
without using its entire key?
No. An entity is uniquely identified only by its entire key, which includes the keys of all the parent entities. If you know the kinds of its parent entities, though, you can use db.Key.from_path to construct the key from the chain of IDs or key names.
I had your same problem but in ndb.Model and I found that I need to convert the ID to an int. So maybe using version.Version.get_by_id(int(34)) can solve your problem.