I am debugging some MATLAB code, and want to make sure that two references to an object are actually referring to the same object. Is there a way to obtain a unique identifier for the objects (such as a memory address)?
As far as I know I am not able to add my own IDs to the objects, as they are MATLAB random number streams.
If you are using OOP then you could add a property ID and set it during the construction of the object.
java.rmi.server.UID() is a nice way to obtain unique ID's
However testing by == will check the actual handles, so this is more of a usability issue.
classdef yourClass < handle
properties
ID
end
methods
function obj = yourClass()
obj.ID = java.rmi.server.UID();
end
end
end
It will then be rather simple to check your objects.
If the objects you're wanting to compare are MATLAB random number streams (i.e. they are of class RandStream), then they are handle objects. In that case you don't need unique IDs: if you compare them using eq or == and they are equal, then they are the same object.
As you say, you are not able to add your own properties to an object of class RandStream, but if you really wanted to you could subclass RandStream and add a property of your own to the subclass. You could store a unique identifier in the property, generated with char(java.util.UUID.randomUUID).
You can use the UserData field, which is present in every graphical object, to store a unique identity generated by you. If working with a user-defined class, you can add a similar field in your class.
The identities can be kept unique by using a global counter to assign each new identity.
Related
I'm currently trying to work out the best way to architect my realm objects for ease of retrieval.
I have 2 objects tags and object there are multiple tags and each one might contain many object. Similarly each object could have multiple tag associated with it
Ideally selecting a single tag should retrieve all object that have at least that one tag (but could obviously have multiple)
would my models be specified as
class Tag: Object {
let objects = List<Object>()
}
class Object {
let tags = List<Tag>()
}
I don't think I need to use an inverse relationship here or should I? Choosing a Category I should be able to just retrieve a list of all object references regardless, but then maintaining and updating the references to an object might be difficult here? I.e a user selects tag 'A' then updates the first object to also include tag 'B' I would need to update the object in the List for Tag A, then add a new item to the list for Tag 'B' and finally update the actual Object itself to include Tag 'B' in it's list of tags.
Just to be clear an Object will only ever display and allow editing of it's Tag objects. But the Tag object itself will need to know what Object's are applicable to it.
However it feels like I will have to do multiple updates when ideally I'd like to minimise this effort. Can anyone recommend a better way to do this? Or is there no way around this due to the limitations of Realm?
This is exactly what LinkingObjects is for. Changing the objects property in Tag to let objects = LinkingObjects(fromType: Object.self, property: "tags") will make it automatically update whenever a tag is added to an object.
I am just starting out with CodeFluent and beginning to really like it. My question is: I set a property of an entity to enumeration. How can I allow an end-user to add extra values (that are stored afterwards as additional choices) to an enumeration? Or should I use another entity to store those values/choices instead?
For instance: let's say I have a product and a producttype. My producttype is an enumeration (frozen, fresh, seasonal), and down the road, the user wants additional types (i.e.: organic, stationary). Should those be enumeration values or a separate entity?
If a separate entity.....I'm not really sure how I define the relationship (1 to 1, 1 to many - i.e. 1 producttype can have many products)?
You can't add values to an enum at runtime, that's impossible in .NET, so it's also impossible with CodeFluent.
So, you want to create another entity that will store the list of enums. That would be a 1:M relation. This is how you would layout that relation:
Each enumeration value would be a row in the ProductType table. With CodeFluent, you can declare "instances" for an entity that will become rows in the final table, so here, you can declare your initial enum values using instance, so use the instance grid on the ProductType entity, and add instances:
Note in this case, maybe you want to create the ProductType's Id property as an int without identity (if you don't want those enum int values generated by the database).
I need to do group by on list of objects based multiple attributes in the object.
like lets say there is a student object
with attributes name,number,state,city,marks
now i need to do group by on it based on multiple keys,
like
it cab be state,city or state or name,state,city or marks,count(*)
Please let me know the best option to do it.
the possible options i have are.
1) using of Nested maps
2) using multimap with composite key
3) using ArrayTable.
Seems like just do a list per criteria. Otherwise I might create an Enum that implements Predicate and create a Multimap with the enum as the key.
Hey, what i want to do is to make a int that will be the ID of the entity and auto increment itself whenever a new entity is added (just like a SQL identity property). Is this possible? i tried using indexed (checked on attribute) however there is no description to what indexed even does.
EDIT:
I am adding annotations to a map, when you click the pin the annotationview with a chevron shows up. Now when you click this button i would like to load an associated picture. However the only way i know how to link the picture to this button is to give the picture a unique id, and then set the button.tag to this id and then load based on the button.tag.
This kind of concept is contrary to the principles of Core Data - the idea is that you're managing sets of entities with properties, not rows in a database or other things that need to be uniqued. (If you're using the SQLite store, Core Data will create an ID for you behind the scenes, but you can't access it.)
You should probably reconsider (or at least give more details about) the problem you're trying to solve, because as it stands, Core Data will not let you autoincrement a variable.
If you absolutely must, you can manually increment on insert by having some NSNumber ID field on your entity, then every time you insert a new entity, get the existing entities sorted by that ID and limited to one result (using a NSFetchRequest with various options), grab that entity's ID, add one, and set it as the new entity's ID. It's a lot of work, though, and probably error-prone.
Edit: Based on the extra information, I'd say rather than trying to autoincrement an ID yourself, find some other guaranteed-unique property of the annotation and either use that directly or write a hash function that uses it to generate your unique ID. For example, use the latitude & longitude to build a single integer that uniquely represents that point within your system. Other than that, there's no way around having to increment the ID yourself.
I agree that this is a sticky problem - I haven't ever come across something like this in Core Data before, and I can see where autoincrementing might be useful :)
This is the simplest way, but takes some effort.
Create an "index" attribute in your Entity. Make it a String
When you create a new one, generate a GUID using CFUUIDCreate() and CFUUIDCreateString()
Assign the GUID to the "index" attribute
Voila, you now have a nearly-perfect unique ID, ready to use for caching locally and using as needed
CFUUIDRef uuidRef = CFUUIDCreate(kCFAllocatorDefault);
CFStringRef uuidStringRef = CFUUIDCreateString(kCFAllocatorDefault, uuidRef);
NSString* guidString = [NSString stringWithString:(__bridge NSString*)uuidStringRef];
Example: I read data from an XML file. This data has unique id elements. I want to store those objects with their original unique id. How would I do that?
I figured out I could ask the managed object for it's ID, like this:
NSManagedObjectID *moID = [managedObject objectID];
but here the problem is: The XML tells me with the id element which object this is, and I need to look up in the database of core data if this object already exists in there, or not. So is it the only option to make an id attribute in my managed object model for that entity and then query for that? Then I will have two id systems right?
Don't worry about the ObjectID of Core Data. This is an internal unique ID which is not guarantied to be constant during the object's life cycle (e.g. it will change when you save the object to sql store). Just create a new mandatory attribute in your model and flag it as indexed so retrieval will be fast.
In the entity associated to this kind of objects, simply add another attribute of type string, call it objectID or similar and declare it to be mandatory.