I'm working on a 2-tier WPF/EF Code First application. I did a lot of googling but couldn't find a sample implementation of what I was looking for... was hoping that someone on this forum could help me out. Here are the requirements:
On Application Start up
Open a DBContext
Cache the reference data in various maps/lists when the application starts
Close Context.
When user opens a form
Open a DBContext (I'm using UnitOfWork pattern here)
Fetch a fresh copy of Entity from context for Editing.
Call SaveChanges() when Save button is hit.
Close the Context.
The problem manifests when I use an object from Cache to change a navigation property.
e.g. use a drop down (backed by cache which was created using a different DBContext) to set Department navigation property.
The UnitOfWork either throws an exception saying entity was loaded in another DBContext (When Department is lazy loaded DynamicProxy) or inserts a new row in Department table.
I couldn't find even a single example where reference data was being cached... I can't believe that no one came across this issue. Either I'm not looking in the right place or not using the right keywords.
I hope this is doable using EF. I'd appreciate if you can share your experiences or post some references.
I'm kinda new to this so would like to avoid using too many frameworks and just stick to POCO with WPF/EF stack.
Try to attach your cached item (probably, you'd make a clone before attaching):
var existingUnicorn = GetMyExistingUnicorn();
using (var context = new UnicornsContext())
{
context.Unicorns.Attach(existingUnicorn);
context.SaveChanges();
}
Refer to Using DbContext... article.
You mention you are using WPF for this, in that case you don't necessarily have to open a new DBContext every time you want to interact with the domain layer. (Apologies if this goes against UoW that you are keen on using)
Personally I have been using code-first development for a desktop application, and I have found that pooling the contexts (and therefore the connection) prevents this problem, and hasn't led to any problems thus far.
In principle, as soon as the application is launched, a main Context object is opened for the main UI thread, and stays open throughout the duration of the application lifetime. It is stored statically, and is retrieved by any Repository class when they are used.
For multi-threading scenarios, any background threads are free to open up additional contexts and use them in Repositories to prevent any race conditions.
If you were to adopt this approach, you would find that as all repositories share the same context, there are no issues arising from object context tracking.
I ended up defining int foreign key property in addition to navigation.
In my application I only modify the int property and use the navigation property for displaying the details (read only controls).
While this works it makes the application a little fragile and sometimes inconsistent.
although this blog claims that the FK & Navi properties are synced by EF but I couldn't get it to work.
http://coding.abel.nu/2012/03/ef-code-first-navigation-properties-and-foreign-keys
Related
I have a web application developed with JSF 2 and primefaces. The project has been frozen for months, but it's quite advanced, the whole application run inside the same container under glassfish, so it's a monolith.
My application has an user interface and its purpose is to offer them the possibility to organize urls to tutorials (any kinds) as cards, with tags for the classification, into folders. So any user has its own tree, they can make a research inside the other users's tree create a link on a file in their own tree, copy a entire folder, reorganize it etc.
Nowedays we hear a lot about microservices, Spring boot, Angular Js, react etc. I like to develop with JSF it's a great framework, but I'm asking myself about refactoring my application, at least the necessary parts into microservices, and if JSF is appropriate for that or if I should user other tools.
What I like for example with JSF is the facility to create views, its component approach, and how it handle the full cycle of a request.
For example with a simple folder creation form :
I have to choose the parent folder, so I can bind a research component to a backing bean that makes a research indirectly in my DB using a DAO ( in my app an EJB using JPA). That happens at the "invoke application" phase and refresh my form list with ajax at the end. When I submit the form I can also bind a converter to the research component to retrieve directly a Folder object, the converter uses also a DAO to retrieve the object that I need at the "Invoke application" phase to finish the job.
I also use validators to control different attributes of a new folder, usually I declare them inside my entity class (Folder, User ...) with annotations like #NotNull etc. Before I save the folder on my db, I also check the user rights to see if he can write inside the parent folder and so on. I do that inside the backing bean, so at the 'invoke application' phase, and return a faces message if anything happens wrong.
When I read about micro-services I see that you can use them directly inside a form using json for communication, so it seems quite different. For example if I have a micro-service for the CRUD operations of my folders, are the validators, the converters, part of the service or are they stand alone services ? And what about the security checks ? that kind of architecture is quite mysterious to me.
ps : English is not my mother tongue so be indulgent please :)
AngularJs is pretty ancient man :)
You have to look at the pain points to identify ways to tear down your monolith. Monolith pains are usually slow and painful dev cycle and difficult manual test phases. If you did the entire arquillian thing and have full continuouos integration with single button deployments, you've slain the beast the hard way. Not many braved this route. But if you're looking at mounting feature creep with code freezes and manual test cycles then yeah you kind of want to try to pull some of those features out into a service you can redeploy very quickly
I´m developping a project using WPF + MVVM.
The program needs to load objects (cases) from a repository and allow the user to edit it.
The main functionalities are:
CRUD of cases
Know which cases have been loaded
Know which case is currently selected
Currently, the version 0.1 uses a singleton class Session (in namespace model) to store a list from all cases loaded.
There is also a "Case Management" service that perform several operations in the Session singleton:
Load a case from the repository and store it in Session
Remove cases
Verify if a case is valid
Select a case for editing
I´m new to WPF, and I would like to know if there is a design pattern that is suitable for this situation. I´m afraid that I´m not going to the right direction.
I dont know if I have provided all information needed, but I´m willing to answer any question as fast as I can.
Your design is fine, i can't see anything wrong.
I would suggest one thing though, get rid of that singleton session object and use dependency injection, and let the DI container decide what life strategy to use for the Session object at the application composition root.
I hope your case management service is using some kind of ORM . If yes, then it will automatically take care of your Load Case/ Return Case and storing it into the session. And depending on user input when you want to get something from the session and you can use Dependency Injection principle (i would suggest to use Ninject) and achieve it with a singleton pattern .
Can anyone give a high level description of what is going on in the Composite C1 core? In particular I am interested in knowing how the plugin architecture works and what the core components are of the system i.e. when a request arrives what is happening in the architecture. The description doesn't have to be too verbose just a list of steps and the classes involved.
Hopefully one of the core development team would enlighten me... and maybe publish some more API (hint hint more class documentation please).
From request to rendered page
The concrete path a request takes depends on the version of C1 you're using, since it was changed to use Routing in version 2.1.2. So lets see
< 2.1.2
Composite.Core.WebClient.Renderings.RequestInterceptorHttpModule will intercept all incoming requests and figure out if the requested path correspond to a valid C1 page. If it does, the url will be rewritten to the C1 page handler ~/Rendererings/Page.aspx
2.1.1
Composite.Core.Routing.Routes.Register() adds a C1 page route (Composite.Core.Routing.Pages.C1PageRoute) to the Routes-collection that looks at the incoming path, figures out if its a valid C1 page. If it is, it returns an instance of ~/Rendererings/Page.aspx ready to be executed.
Okay, so now we have an instance of a IHttpHandler ready to make up the page to be returned to the client. The actual code for the IHttpHandler is easy to see since its located in ~/Renderers/Page.aspx.cs.
OnPreInit
Here we're figuring out which Page Id and which language that was requested and looking at whether we're in preview mode or not, which datascope etc.
OnInit
Now we're fetching the content from each Content Placeholder of our page, and excuting its functions it may contain. Its done by calling Composite.Core.WebClient.Renderings.Page.PageRenderer.Render passing the current page and our placeholders. Internally it will call the method ExecuteFunctions which will run through the content and recursively resolve C1 function elements (<f:function />), execute them and replace the element with the functions output. This will be done until there are no more function elements in the content in case functions them selves output other functions.
Now the whole content is wrapped in a Asp.Net WebForms control, and inserted into our WebForms page. Since C1 functions can return WebForms controls like UserControl etc., this is necessary for them to work correctly and trigger the Event Lifecycle of WebForms.
And, that's basically it. Rendering of a requested page is very simple and very extendable. For instance is there an extension that enables the usage of MasterPages which simply hooks into this rendering flow very elegantly. And because we're using Routing to map which handler to use, its also possible to forget about ~/Rendering/Page.aspx and just return a MvcHandler if your a Mvc fanatic.
API
Now, when it comes to the more core API's there are many, depending on what you want to do. But you can be pretty sure, no matter what there is the necessary ones to get the job done.
At the deep end we have the Data Layer which most other API's and facades are centered around. This means you can do most things working with the raw data, instead of going through facades all the time. This is possible since most configuration of C1 is done by using its own data layer to store configuration.
The Composite C1 core group have yet to validate/refactor and document all the API's in the system and hence operate with the concept of 'a public API' and what can become an API when the demand is there. The latter is a pretty darn stable API, but without guarantees.
The public API documentation is online at http://api.composite.net/
Functions
Functions is a fundamental part of C1 and is a technique to abstract logic from execution. Basically everything that either performs a action or returns some data/string/values can be candidates for functions. At the lowest level a function is a .Net class implementing the IFunction interface, but luckily there are many easier ways to work with it. Out of the box C1 supports functions defined as XSLT templates, C# methods or Sql. There are also community support for writing functions using Razor or having ASP.Net UserControls (.ascx files) to be functions.
Since all functions are registered in C1 during system startup, we use the Composite.Functions.FunctionFacade to execute whatever function we know the name of. Use the GetFunction to get a reference to a function, and then Execute to execute it and get a return value. Functions can take parameters which are passed as real .Net objects when executing a function. There is also full support for calling functions with Xml markup using the <f:function /> element, meaning that editors, designers, template makers etc. easily can access a wealth of functionality without having to know how to write .Net code.
Read more about functions here http://users.composite.net/C1/Functions.aspx and how to use ie Razor to make functions here http://docs.composite.net/C1/ASP-NET/Razor-Functions.aspx
Globalization and Localization
C1 has full multi-language support in the core. Composite.Core.Localization.LocalizationFacade is used for managing the installed locales in the system; querying, adding and removing. Locales can be whatever CultureInfo object is known by your system.
Composite.Core.ResourceSystem.StringResourceSystemFacade is used for getting strings at runtime that matches the CultureInfo your request is running in. Use this, instead of hardcoding strings on your pages or in your templates.
Read more about Localization here http://docs.composite.net/C1/HTML/C1-Localization.aspx
Global events
Composite.C1Console.Events.GlobalEventSystemFacade is important to know if you need to keep track on when the system is shutting down so you can make last-minute changes. Since C1 is highly multithreaded its easy to write extensions and modules for C1 that are multithreaded as well, taking advantage of multi core systems and parallelization and therefor its also crucial to shut down ones threads in a proper manner. The GlobalEventSystemFacade helps you do that.
Startup events
If you write plug-ins these can have a custom factory. Other code can use the ApplicationStartupAttribute attribute to get called by the Composite C1 core when the web app start up.
Data events
You can subscribe to data add, edit and delete events (pre and post) using the static methods on Composite.Data.DataEvents<T>. To attach to these events when the system start up, use the ApplicationStartupAttribute attribute.
Data
Composite.Core.Threading.ThreadDataManager is important if your accessing the Data Layer outside of a corresponding C1 Page request. This could be a custom handler that just has to feed all newest news as a Rss feed, or your maybe writing a console application. In these cases, always remember to wrap your code that accesses the data like this
using(Composite.Core.Threading.ThreadDataManager.EnsureInitialize())
{
// Code that works with C1 data layer goes here
}
For accessing and manipulating data its recommended NOT to use the DataFacade class, but wrap all code that gets or updates or deletes or adds data like this
using(var data = new DataConnection())
{
// Do things with data
}
IO
When working with files and directories its important to use the C1 equivalent classes Composite.Core.IO.C1File and Composite.Core.IO.C1Directory to .Net's File and Directory. This is due to the nature where C1 can be hosted on Azure, where you might not have access to the filesystem in the same way as you have on a normal Windows Server. By using the C1's File and Directory wrappers you can be sure that code you write will be able to run on Azure as well.
C1 Console
The console is a whole subject on itself and has many many API's.
You can create your own trees using Composite.C1Console.Trees.TreeFacade or Composite.C1Console.Elements.ElementFacade and implementing a Composite.C1Console.Elements.Plugins.ElementProvider.IElementProvider.
You can use the Composite.C1Console.Events.ConsoleMessageQueueFacade to send messages from the server to the client to make it do things like open a message box, refreshing a tree, set focus on a specific element, open a new tab etc. etc.
Composite.C1Console.Workflow.WorkflowFacade is used for getting instances of specific workflows and interacting with them. Workflows is a very fundamental part of C1 and is the way multi-step operations are defined and executed. This makes it possible to save state of operation so ie. a 10 step wizard is persisted even if the server restarts or anything else unexpected happens. Workflows are build using Windows Workflow Foundation, so are you familiar with this, you should be feeling at home
There is also a wealth of javascript facades and methods you can hook into when writing extensions to the Console. Much more than i could ever cover here so i will refrain myself from even getting started on that subject here.
composite.config
A fundamental part of C1 is providers, almost everything is made up of providers, even much of the core functionality. Everything in the console from Perspectives to Trees and elements and actions are feeded into C1 with providers. All the standard functions, the datalayer and all the widgets for use with the Function Call editor is feeded into C1 with providers. All the localisation strings for use with the Resources, users and permissions, url formatters etc. is all providers.
Composite.Data.Plugins.DataProviderConfiguration
Here all providers that can respond to the methods on DataFacade, Get, Update, Delete, Add etc. are registered. Every provider informs the system which interfaces it can interact with and C1 makes sure to route all requests for specific interfaces to their respective dataproviders.
Composite.C1Console.Elements.Plugins.ElementProviderConfiguration
Here we're defining the perspectives and the trees inside the Console. All the standard perspectives you see when you start the Console the first time are configured here, no magic or black box involved.
Composite.C1Console.Elements.Plugins.ElementActionProviderConfiguration
Action providers are able to add new menuitems to all elements in the system, based on their EntityToken. This is very powerful when you want to add new functionality to existing content like versioning, extranet security, custom cut/paste and the list goes on.
Composite.C1Console.Security.Plugins.LoginProviderConfiguration
A LoginProvider is what the C1 console will use to authenticate a user and let you log in or not. Unfortunately this isn't very open but with some reflection you should be all set.
Composite.Functions.Plugins.FunctionProviderConfiguration
Composite C1 will use all the registered FunctionProviders to populate its internal list of functions on system startup.
Composite.Functions.Plugins.WidgetFunctionProviderConfiguration
WidgetProviders are used in things like the Function Call Editor or in Forms Markup to render custom UI for selecting data.
Composite.Functions.Plugins.XslExtensionsProviderConfiguration
Custom extensions for use in XSLT templates are registered here
And then we have a few sections for pure configuration, like caching or what to to parallelize but its not as interesting as the providers.
Defining and using sections
Sections in composite.config, and other related .config files are completely standard .Net configuration and obeys the rules thereof. That means that to be able to use a custom element, like ie. Composite.Functions.Plugins.WidgetFunctionProviderConfiguration it has to be defined as a section. A section has a name and refers to a type that would inherit from System.Configuration.ConfigurationSection. Composite uses the Microsoft Enterprise Libraries for handling most of these common things like configuration and logging and validation and therefor all Composites sections inherit from Microsoft.Practices.EnterpriseLibrary.Common.Configuration.SerializableConfigurationSection. Now, this type just has to have properties for all the elements we want to be able to define in the .config-file, and .Net will automatically make sure to wire things up for us.
If you want to access configuration for a particular section you would call Composite.Core.Configuration.ConfigurationServices.ConfigurationSource.GetSection(".. section name") and cast it to your specific type and your good to go.
Adding extra properties to already defined sections
Normally .Net would complain if you write elements or attributes in the .config files that aren't recognized by the type responsible for the section or for the element. This makes it hard to write a truly flexible module-system where external authors can add specific configuration options to their providers, and therefor we have the notion of a Assembler. Its a ConfigurationElement class with a Microsoft.Practices.EnterpriseLibrary.Common.Configuration.ObjectBuilder.AssemblerAttribute attribute assigned to it that in turns takes a Microsoft.Practices.EnterpriseLibrary.Common.Configuration.ObjectBuilder.IAssembler interface as argument that is responsible for getting these custom attributes and values from the element in the .config file and emit usable object from it. This way .Net won't complain about an invalid .config file, since we inject a ConfigurationElement object that has properties for all our custom attributes, and we can get hold of them when reading the configuration through the IAssembler
Slides
Some overview slides can be found on these lins
Overview
Extensibility points
Page request handling
Function system
Data system
Data type system
Inspiration and examples
The C1Contrib project on GitHub is a very good introduction how to interact with the different parts of C1. Its a collection of small packages, that can be used as it is, or for inspiration. There are packages that manipulates with dynamic types to enable interface inheritance. Other packages uses the javascript api in the console, while others show how to make Function Providers, Trees and hook commands unto existing elements. There is even examples of how to manipulate with the Soap webservice communication going on between client and server so you can make it do things the way you want it. And the list goes on.
I have a class running in a winforms app which uses EF Code First. The DbContext is created via DI through the class constructor. All works well.
The problem is the data being referenced is also being modified via a web site, using the same DI pattern with EF Code First, and the data changes are not being reflected in the context instance in the winforms app.
I can solve this by recreating the DbContext object in winforms every time I access it, but seems to be more of a service location pattern to me?
Is there a true DI technique to achieve this?
Or should I remove the context from the DI and use service location?
Were you not happy with the answer to your other question (http://stackoverflow.com/questions/7657643/how-to-force-ef-code-first-to-query-the-database) which suggested using Detach, AsNoTracking or Overwrite Changes?
1) Maybe you could pass an interface that has the ability to create a DbContext, instead of the context itself.
using(var context = _contextFactory.Create()) {
var entity = from table in context.Blah...;
}
The Create method could either create the concrete class itself (defeating the DI pattern a bit), or use service location to have one created for it. Not that nice, but it's better than embedding service location calls everywhere and still means you're controlling the lifecycle yourself.
2) Change the WinForm to read from a webservice run by the website, effectively similar to disabling caching.
3) Deep in the heart of MVC (well not really that deep) it is referencing the DI container directly and using it as a service locator to pass as arguments for newly created objects. Technically you could do something similar in WinForms, but it would need you to split your application up into little chunks (controllers) that don't have a very long lifetime. Maybe it's worth looking at some MVC/MVP frameworks for WinForms, although I found myself cringing at most I saw after a quick google.
The problem is the data being referenced is also being modified via a web site, using the same DI pattern with EF Code First, and the data changes are not being reflected in the context instance in the winforms app.
This is a problem with your expectations.
If your web service and window forms app are in separate processes, they won't share in-memory data.
If you want to sync their in-memory data, simply re-query in one context after committing to the database in the other. This is the same as trying to share data between different SQL connections.
I can solve this by recreating the DbContext object in winforms every time I access it, but seems to be more of a service location pattern to me?
If you want to recreate the DbContext repeatedly, you could use an abstract factory to allow manual re-creation of the object, yet allow you to inject the specific implementation into the factory.
This is not (necessarily) the Service Locator pattern, and you would have to ensure that you manually dispose your DbContext instances. I'd give you some example code, but different DI containers have totally different ways of accomplishing a factory pattern.
Or you could simply make sure that you commit your data on the web service side, and re-query the data on the WinForms app side.
For past projects(the last few have been web using asp.net mvc) we created a service that caches our reference tables(as required) to be used primarily for dropdown lists.
Now I'm working on a desktop application.An upgrade from vb6/sybase to vb.net/sql server
I'm trying out WPF.
I started down the same path building up my DAL. one entity for each reference table.
I'm at the stage now where I want to setup the business layer (some reference tables can be edited)
And I'm not sure if I should follow the same process which is to use ReferenceTableService to "manage" the reference tables.(interacts with the DAL, Controller)
This will be an application that sits on a share that multiple users run.
What's the best way to deal with the reference tables? Caching them doesn't seem to be an option. Should I simply load them as each user opens up a new form in the application? Perhaps using a "ReferenceTableService"?
In this case, the Reference Table Service is thin layer in the application. Not a process running elsewhere.
I haven't done much WPF (be interesting to see what the WPF Gurus think) but I think your existing approach is sound and I don;t see why you should deviate from it.
Loading up on app start sounds reasonable; you just have to think about the expected lifetime of a user session vs the expected frequency of changes to the reference data.
Caching: if the data comes from a central service you could always introduce caching there.