I am using the Three.js Object3D userData property to store information from a MySQL database serialized into json pairs to give me data to perform various actions when selecting objects which represent saved data. It seems to work nicely for a few pairs.
I note from the reference a warning to not to store references to functions as they will not be cloned. Can anyone tell me if there any other limitations to this property (number of pairs, hierarchical data, etc.)? I want to store 2-3000 words of text, images, blobs etc., but prefer to ask over trial and error. the documents are a little sparse on such matters.
Many thanks... James
No there are not special limitations. It is simply a Javascript object:
https://github.com/mrdoob/three.js/blob/0fbc8afb348198e4924d9805d1d4be5869264418/src/core/Object3D.js#L85
this.userData = {};
So while your object is in memory, you can put any Javascript variables there. Only limitations are what you always have, the available memory basically. As Javascript objects can contain any types and hierarchy so you're off fine there.
I used this search to check this in the codebase: https://github.com/mrdoob/three.js/search?utf8=%E2%9C%93&q=userdata
Related
When someone talks about hydrating an object, what does that mean?
I see a Java project called Hydrate on the web that transforms data between different representations (RDMS to OOPS to XML). Is this the general meaning of object hydration; to transform data between representations? Could it mean reconstructing an object hierarchy from a stored representation?
Hydration refers to the process of filling an object with data. An object which has not yet been hydrated has been instantiated and represents an entity that does have data, but the data has not yet been loaded into the object. This is something that is done for performance reasons.
Additionally, the term hydration is used when discussing plans for loading data from databases or other data sources. Here are some examples:
You could say that an object is partially hydrated when you have only loaded some of the fields into it, but not all of them. This can be done because those other fields are not necessary for your current operations. So there's no reason to waste bandwidth and CPU cycles loading, transferring, and setting this data when it's not going to be used.
Additionally, there are some ORM's, such as Doctrine, which do not hydrate objects when they are instantiated, but only when the data is accessed in that object. This is one method that helps to not load data which is not going to be used.
With respect to the more generic term hydrate
Hydrating an object is taking an object that exists in memory, that doesn't yet contain any domain data ("real" data), and then populating it with domain data (such as from a database, from the network, or from a file system).
From Erick Robertson's comments on this answer:
deserialization == instantiation + hydration
If you don't need to worry about blistering performance, and you aren't debugging performance optimizations that are in the internals of a data access API, then you probably don't need to deal with hydration explicitly. You would typically use deserialization instead so you can write less code. Some data access APIs don't give you this option, and in those cases you'd also have to explicitly call the hydration step yourself.
For a bit more detail on the concept of Hydration, see Erick Robertson's answer on this same question.
With respect to the Java project called hydrate
You asked about this framework specifically, so I looked into it.
As best as I can tell, I don't think this project used the word "hydrate" in a very generic sense. I see its use in the title as an approximate synonym for "serialization". As explained above, this usage isn't entirely accurate:
See: http://en.wikipedia.org/wiki/Serialization
translating data structures or object state into a format that can be stored [...] and reconstructed later in the same or another computer environment.
I can't find the reason behind their name directly on the Hydrate FAQ, but I got clues to their intention. I think they picked the name "Hydrate" because the purpose of the library is similar to the popular sound-alike Hibernate framework, but it was designed with the exact opposite workflow in mind.
Most ORMs, Hibernate included, take an in-memory object-model oriented approach, with the database taking second consideration. The Hydrate library instead takes a database-schema oriented approach, preserving your relational data structures and letting your program work on top of them more cleanly.
Metaphorically speaking, still with respect to this library's name: Hydrate is like "making something ready to use" (like re-hydrating Dried Foods). It is a metaphorical opposite of Hibernate, which is more like "putting something away for the winter" (like Animal Hibernation).
The decision to name the library Hydrate, as far as I can tell, was not concerned with the generic computer programming term "hydrate".
When using the generic computer programming term "hydrate", performance optimizations are usually the motivation (or debugging existing optimizations). Even if the library supports granular control over when and how objects are populated with data, the timing and performance don't seem to be the primary motivation for the name or the library's functionality. The library seems more concerned with enabling end-to-end mapping and schema-preservation.
While it is somewhat redundant vernacular as Merlyn mentioned, in my experience it refers only to filling/populating an object, not instantiating/creating it, so it is a useful word when you need to be precise.
This is a pretty old question, but it seems that there is still confusion over the meaning of the following terms. Hopefully, this will disambiguate.
Hydrate
When you see descriptions that say things like, "an object that is waiting for data, is waiting to be hydrated", that's confusing and misleading. Objects don't wait for things, and hydration is just the act of filling an object with data.
Using JavaScript as the example:
const obj = {}; // empty object
const data = { foo: true, bar: true, baz: true };
// Hydrate "obj" with "data"
Object.assign(obj, data);
console.log(obj.foo); // true
console.log(obj.bar); // true
console.log(obj.baz); // true
Anything that adds values to obj is "hydrating" it. I'm just using Object.assign() in this example.
Since the terms "serialize" and "deserialize" were also mentioned in other answers, here are examples to help disambiguate the meaning of those concepts from hydration:
Serialize
console.log(JSON.stringify({ foo: true, bar: true, baz: true }));
Deserialize
console.log(JSON.parse('{"foo":true,"bar":true,"baz":true}'));
In PHP, you can create a new class from its name, w/o invoke constructor, like this:
require "A.php";
$className = "A";
$class = new \ReflectionClass($className);
$instance = $class->newInstanceWithoutConstructor();
Then, you can hydrate invoking setters (or public attributes)
We have followed the step-by-step tutorials for the model-derivative apis. I can use the /manifest endpoint to get the object tree. I can also create tasks to get a .obj file with geometries of some objects. There is no way to know which geometry belongs to which object.
I could potentially create a job for each object, but that would require thousands of jobs per model which seems excessively inefficient. Are we missing something? Any pointers on how to get geometry for objects while retaining the mapping between them?
The Viewer will extract the information, but as of today, we don't have a documentation for SVF, so it may get trickier to analyze the geometry from this file. You may use JavaScript, something like described in this sample or this sample.
You can extract the OBJs for each element, but may need a big number of jobs. In this case, you need to run your code for .obj files.
I have a huge amount of data, already stored in STL containers. It feels very bad to do full copy for all data to Gtk::ListStore. And also, my data structure contains big gaps in some rows, which simply can be filled with a default value if the line of the view becomes visible. To store tons of default values into a model is also a bad overhead.
For this I thought it is easy to setup a own model which will then provide some entry points/callbacks where I simply can provide my own data from my containers.
But I can not find any line of documentation.
Here a standard TreeView, but no idea how to improve with own model:
https://developer.gnome.org/gtkmm-tutorial/stable/sec-treeview-examples.html.en
In https://developer.gnome.org/gtkmm-tutorial/stable/sec-treeview-model.html.en I found the beautiful sentence
Although you can theoretically implement your own Model,
you will normally use either the ListStore or TreeStore model classes.
After that I take a look into the sources... well, because Gtkmm is only a wrapper over the C-code, it is not simply deriving from a class and overwrite some methods. It is more to pick up the underlaying c code if my interpretation of the code I saw is correct.
Anyway, is there any chance to get some lines of code where the ListStore is replaced by a own model?
I used the isolated storage before to save text files, xml files and images. However, is it possible to save variables of type IEnumerable using IsolatedStorage or any other resource in windows phone 7??
Thanks,
You are misunderstanding core concepts.. There is no such thing as "saving variables", you save objects. Your variable points to an object, and that objects implements IEnumerable. Is On WP7, it is the object's actual class that determines whether that object can be serialized and stored on the ISO directly. If that actual collection class does not support serialization, you will have to re-wrap all its current elements into a List/Array/Dictionary/Stack/Queue - literally whatever what supports being serialized - and store that instead of.
Once you have an serializable collection, then your code for saving gets reduced to something as trivial as:
IsolatedStorageSettings.ApplicationSettings["blah"] = your_serializable_collection;
IsolatedStorageSettings.ApplicationSettings.Save();
and in general, that's it. Retrieving is similar:
var items = (SomeCollection)IsolatedStorageSettings.ApplicationSettings["blah"];
where SomeCollection may be an IEnumerable, a List/Array/Dictionary/Stack/Queue - whatever you had put there and whatever is implemented by the actual collection class.
If you want, you may use IsolatedStorageFile and write files directly, but unless you have a good reason to - there's no point in it, as using the common dictionary is far simplier.
In my other post you'll find some links:
How to do isolated storage in Wp7?
Use for saving/loading of data List which are serializable out of the box. Last time i tried deserialize an IEnumerable I got errors...
I'm trying to figure out how to decide when to use NSDictionary or NSCoder/NSCoding?
It seems that for general property lists and such that NSDictionary is the easy way to go that generates XML files that are easily editable outside of the application.
When dealing with custom classes that holds data or possibly other custom classes nested inside, it seems like NSCoder/NSCoding would be the better route since it will step through all the contained object classes and encode them as well when an archive command is used.
NSDictionary seems like it would take more work to get all the properties or data characteristics to a single level to be able to save it, where as NSCoder/NSCoding would automatically encode nested custom classes that implement the NSCoding interface.
Outside of it being binary data and not editable outside of your application is there a real reason to use one over the other? And along those lines is there an indicator of which way you should lean between the two? Am I missing something obvious?
Apple's documentation on object graphs has this to say:
Mac OS X serializations store a simple hierarchy of value objects, such as dictionaries, arrays, strings, and binary data. The serialization only preserves the values of the objects and their position in the hierarchy. Multiple references to the same value object might result in multiple objects when deserialized. The mutability of the objects is not maintained.
…
Mac OS X archives store an arbitrarily complex object graph. The archive preserves the identity of every object in the graph and all the relationships it has with all the other objects in the graph. When unarchived, the rebuilt object graph should, with few exceptions, be an exact copy of the original object graph.
The way I interpret this is that, if you want to store simple values, serialization (using an NSDictionary, for example) is a fine way to go. If you want to store an object graph of arbitrary types, with uniqueness and mutability preserved, using archives (with NSCoder, for example) is your best bet.
You may also want to read Apple's Archives and Serializations Programming Guide for Cocoa, of which the aforelinked page on object graphs is a part, as it covers this topic well.
I am NOT a big fan of using NSCoding/NSCoder/NSArchiver (we need to pick a name!) to serialise an object graph to a file.
Archives created in this way are incredibly fragile. If you save an object of class Foo then by golly you need to make sure when you load the data back in you have a class Foo in your application.
This makes NSCoder based serialisation difficult from the perspective of sharing files with other applications or even forwards compatibility with your future application.
I forgot to list what I would recommend.
NSCoding can be ok in certain situations: if you're just doing something quick and simple (although you do have to write a lot of code - two methods per class to be serialised). It can also be ok if you're not worried about compatibility with other applications.
Export/import via property lists (perhaps using the NSPropertyListSerializaion class) is a fine solution. XML based plists are easy to create and edit. Main advantage to plists is that you're not tying the file format to just your application.
You can also create your own XML based file format and read/write to it using NSXMLDocument API and friends. This really isn't much more work than using property lists.
I think you're a bit confused, NSDictionary is a data structure, it also happens to implement the NSCoding protocol. So in essence, you could either put all your data into a NSDictionary and have that encode itself later on, or you can implement the NSCoding protocol and encode your object tree using the NSCoder API. Based on the type of NSCoder object passed in to the encodeWithCoder: method, is the output of your encoding.