Let me begin with an illustrative example (assume the implementation is in a statically typed language such as Java or C#).
Assume that you are building a content management system (CMS) or something similar. The data is hierarchically organised into Folders. Each folder has a collection of children; a child may be a Page or a Folder. All items are stored within a root folder. No cycles are allowed. We have an acyclic graph.
The system will have a remote API and instances of Folder and Page must be serialized / de-serialized across the network. With a typical implementation of folder, in which a folder's children are a List, serialization of the root node would send the entire graph. This is unacceptable for obvious reasons.
I am interested to hear people have solved this problem in the past.
I have two potential suggestions:
Navigation by query: Change the domain model so that the folder class contains only a list of IDs for each child. To access a child we must query for it. Serialisation is now trivial since the graph ends at a well defined point. The major downside is that we lose type safety - the ID could be for something other than a folder/child.
Stop and re-attach: During serialization stop whenever we detect a reference to a folder or page, send the ID instead. When de-serializing we must then look up the corresponding object for each ID and re-attach it at the relevant position in the nascent object.
I don't know what kind of API you are trying to build, but your suggestion #1 sounds like it is close to what is recommended for REST style services and APIs. Basically, a Folder object would contain a list of URLs to its children.
The Navigation by query solution was used for NFS. By reading through your question, it looks to me, as if you're trying to implements kind of a file system yourself.
If you're looking specifically into sending objects over the network there is always CORBA. Aside from that there is DCOM and the newer WCF. But wait there is more like RMI. Furthermore there are Web Services. I'll stop here now.
Suppose You model the whole tree with every element being a Node, specialisations of Node being Folder and, umm, Leaf. You have a "root" Node. Nodes have a methods
canHaveChildren()
getChildren()
Leaf nodes have the obvious behaviours (never even need to hit the network)
Folders getChildren() get the next set of nodes.
I did devise a system with Restful services along these lines. Seemed to be reasonably easy to program to.
I would not do it by the Navigation by query method. Simply because I would like to stick with the domain model where folders contains folders or pages.
Customizing the serialization might also be tricky, bug prone and difficult to change\understand.
I would suggest that you introduce and object like FolderBowser in your model which takes an id and gives you a list of contents of the folder. That will make your service operations simpler.
Cheers,
Unmesh
The classical solution is probably to use a proxy pattern, where some of the graph is sent over the network and some of the folders are replaced by proxies that will not have their lists of children populated until they are queried. A round trip to the server takes a significant amount of time and it will probably result in too many requests if all folders are proxies (this would yield a new request each time the contents of a folder is inspected), so you want to go for some trade off between the size of each chunk of data and the number of server requests needed in a typical scenario. This is of course application specific, but sending the contents of all child folders in for instance depth 2 might be a useful strategy...
Long story short: What will probably work best is your solution #1 with the exception that you want to send more than one folder at a time because of the overhead of a round trip to the server...
Related
I'm trying to let my API clients make a POST request that bulk modifies objects that the client doesn't have their IDs.
I'm thinking of implementing this design but I don't feel good about it, are there any better solutions than this?
POST url/objects/modify?name=foo
This request will modify all objects with the name foo
This can be a tricky thing to do with an API because it doesn't age very well.
By that I mean that over time, you might introduce more criteria for the data stored on resources (e.g., you can only set this field to "archived" if the create_time field is older than 6 months). When that happens, your bulk updates will start to only work on some resources and now you have to communicate that back to the person calling the API.
For example, for any failures you need to explain that the update worked for some resources (and list them out) but failed on others (and list them out) and the reason why for each failure (and remember you might have different failure conditions for different resources).
If you're set on going down this path, the closest thing I can think of is the "criteria-based delete" method shown here: https://google.aip.dev/165.
I built a virtual filesystem (not a namespace extension) for Windows which acts as a frontend of our document management server consisting of files and folders. In order to be able to display some metadata of the DMS objects in Windows Explorer as additional selectable columns, I successfully provided properties to the Windows Property System by implementing a COM Property Handler. Wheras normal property handlers focus on specific file types for which they feel responsible, my Property Handler adds properties to all files regardless of their type. Because Property Handlers can only be registered on the file type level, I registered my handler for about 30 types under
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\PropertySystem\PropertyHandlers\<.Extension>
However, I did not manage to register the Property Handler for folder objects. Since all objects in our file system are virtual I build the property store (IPropertyStore) by implementing IInitializeWithFile instead of IInitializeWithStream. The properties are requested from our DMS with the path of IInitializeWithFile acting as key and were not read from an objects content. This concept would work for folders as well.
For getting called on folders I tried to associate the handler by registering under different well known identifiers like Folder, Directory, AllFileSystemObjects and * instead of the file extension without success.
I also didn’t find anything in the MSDN documentation regarding this aspect.
Is there a way to register a Windows Property Handler on folders? Or is there some other way to add custom columns to folders in Windows Explorer?
I'm not sure if it is possible to do this.
Property handlers are clearly not the right approach, they are system wide and there can only be one per file extension. They should only be implemented by the software that "owns" the file extension and can parse the file to extract properties.
The old column handlers would have been your best bet (IMHO) but they are officially dead and you already said you can't use them.
Have you considered creating a namespace extension? Either as a root item somewhere (Desktop or My Computer) the way My Documents used to work in 2000/XP or maybe something more along the lines of how OneDrive works?
I'm not sure if desktop.ini files work in the root of a drive but it might be worth looking into. You would then find yourself in the poorly documented land of [.ShellClassInfo] and its CLSID, CLSID2 and UICLSID members. The general idea would be to act as a IShellFolder proxy on top of the "real" IShellFolder so you could create a multiplex property store. I think there are some (undocumented?) property keys you can override to change the folders default columns and tooltips as well.
There is also something called a delegated folder that allows you to play with nested PIDLs but the documentation is once again pretty useless so I'm not sure if this is something worth looking into.
A 3rd option is to pretend to be a cloud storage provider. I don't know if this gets you any closer to your goal and you would still have to implement some NSE bits to get to the point where you can layer yourself on top of the underlying IShellFolder. This feature is rather new and only documented to work on Windows 10.
The inner workings of how Explorer/IShellBrowser is connected to the IShellFolder/IShellView is one of the least documented parts of Windows. There are hundreds of undocumented interfaces. Explorer gives DefView special treatment leaving other 3rd-party implementations out in the cold.
My feeling is that there is no clean solution to implement this on top of a drive letter but you might get lucky, if Raymond Chen drops by he might have some tips for you...
First, thanks for any advice. I am new to all of this and apologize for any obvious blunders.
Second, the question:
In an interface for entering clients that often possess a number of roles, it seemed efficient to create a set of inputs which possessed both visual characteristics and associated data binding based simply on the inputs name.
For example, inquirerfirstname would be any caller or emailer who contacted our company.
The name would dictate a label, placeholder, and the location in firebase where the data would be stored.
The single name could be used--I thought--with a relational table (state machine or series of nested ifs) to define the properties of the input and change its outward appearance and inner bindings through property manipulation.
I created a set of nested iffs, and console logged the property changes in the inputs, but their representation in the host element (a collection of inputs that generated messages to clients as well as messages to sales staff) remained unaffected.
I attempted using the ready callback. I forced the state change with a button.
I was unable to use the var name = new MyInput( name). I believe using this method would be most effective but am unsure how to "stamp" the JavaScript into a heavyweight stamped parent element.
An example of a more complicated and dynamic use of a constructor and a factory implementation that can read database (J-son) objects and respond to generate HTML elements would be awesome.
In vanilla a for each would seem to do the trick but definitions and structure as well as binding would not be organic--read it might be easier just to HTML stamp the inputs in polymer by hand.
I would be really greatful for any help. I have looked for a week and failed to find one example that took data binding, physical appearance, attribute swapping, property binding and object reading into account.
I guess it's a lot, but each piece independently (save the use of the constructor) I think I get.
Thanks again.
Jason
Ps: I am aware that the stamping of the element seems to preclude dynamic property attribute and binding assignments. I was hoping a compute attribute mixed with a factoryimpl would be an option (With a nice example).
Passing Data from Page to Page for Windows Phone 8.1
i found this great article :
http://www.windowsapptutorials.com/windows-phone/how-to-pass-data-between-different-pages-in-windows-phone-application/
and i understood it very well,
there are few question i came after reading this article is :
[1] which method is better, in which scenarios ?
[2] what is the benefits of all 3 methods?
Small hint: Please state if you are using Silverlight or WinRT, as it makes a big difference.
I assume you are using Silverlight here.
Like demas already stated: Global variables are almost never a good idea.
Recommendation: Always use queryString and always only pass IDs in the query.
This means, keep your data in some kind of storage and always read it from there on any page.
If you want to pass complex objects, put them to your storage, tell the new page the id and on the new page load it from the storage.
If your app gets terminated (tombstoned) in the background and is
relaunched on your detail-pages, it may always be that your global
variables are empty.
It also improves your maintainability: All data accessed by a page will be loaded on that pages code/codebehind/viewmodel; You don't have to check other parts of the app to find out where that data comes from.
Further hint:
It helped me a lot, to think of a Silverlight app like a "web app": The pages are individual pages and the viemodels are the database servers. There is no way to pass data between these pages other than the query string.
Public property in App.xaml.cs and global variables causes namespace pollution and make the application less testable, so I prefer to use QueryString.
On the other hand, sometimes I need to pass complex object or even collections of complex objects and in this case public property in App.xaml.cs is more preferable in my opinion.
I need some help figuring out the best way to proceed with creating a Rails 3 engine(or plugin, and/or gem).
Apologies for the length of this question...here's part 1:
My company uses an email service provider to send all of our outbound customer emails. They have created a SOAP web service and I have incorporated it into a sample Rails 3 app. The goal of creating an app first was so that I could then take that code and turn it into a gem.
Here's some of the background: The SOAP service has 23 actions in all and, in creating my sample app, I grouped similar actions together. Some of these actions involve uploading/downloading mailing lists and HTML content via the SOAP WS and, as a result, there is a MySQL database with a few tables to store HTML content and lists as a sort of "staging area".
All in all, I have 5 models to contain the SOAP actions (they do not inherit from ActiveRecord::Base) and 3 models that interact with the MySQL database.
I also have a corresponding controller for each model and a view for each SOAP action that I used to help me test the actions as I implemented them.
So...I'm not sure where to go from here. My code needs a lot of DRY-ing up. For example, the WS requires that the user authentication info be sent in the envelope body of each request. So, that means each method in the model has the same auth info hard coded into it which is extremely repetitive; obviously I'd like for that to be cleaner. I also look back now through the code and see that the requests themselves are repetitive and could probably be consolidated.
All of that I think I can figure out on my own, but here is something that seems obvious but I can't figure out. How can I create methods that can be used in all of my models (thinking specifically of the user auth part of the equation).
Here's part 2:
My intention from the beginning has been to extract my code and package it into a gem incase any of my ESP's other clients could use it (plus I'll be using it in several different apps). However, I'd like for it to be very configurable. There should be a default minimal configuration (i.e. just models that wrap the SOAP actions) created just by adding the gem to a Gemfile. However, I'd also like for there to be some tools available (like generators or Rake tasks) to get a user started. What I have in mind is options to create migration files, models, controllers, or views (or the whole nine yards if they want).
So, here's where I'm stuck on knowing whether I should pursue the plugin or engine route. I read Jordan West's series on creating an engine and I really like the thought of that, but I'm not sure if that is the right route for me.
So if you've read this far and I haven't confused the hell out of you, I could use some guidance :)
Thanks
Let's answer your question in parts.
Part One
Ruby's flexibility means you can share code across all of your models extremely easily. Are they extending any sort of class? If they are, simply add the methods to the parent object like so:
class SOAPModel
def request(action, params)
# Request code goes in here
end
end
Then it's simply a case of calling request in your respective models. Alternatively, you could access this method statically with SOAPModel.request. It's really up to you. Otherwise, if (for some bizarre reason) you can't touch a parent object, you could define the methods dynamically:
[User, Post, Message, Comment, File].each do |model|
model.send :define_method, :request, proc { |action, params|
# Request code goes in here
}
end
It's Ruby, so there are tons of ways of doing it.
Part Two
Gems are more than flexible to handle your problem; both Rails and Rake are pretty smart and will look inside your gem (as long as it's in your environment file and Gemfile). Create a generators directory and a /name/name_generator.rb where name is the name of your generator. The just run rails g name and you're there. Same goes for Rake (tasks).
I hope that helps!