Application Insights does not support tracking for MySQL dependencies out of the box, so I would like to add it as my project relies heavily on MySQL.EF6.
Per the documentation here: https://azure.microsoft.com/en-us/documentation/articles/app-insights-api-custom-events-metrics/#track-dependency
It is possible to add tracking, however to avoid having to wrap every call I make to my database, I would like to override the MySQL.EF6 Library functions of SaveChanges, SaveChangesAsync, Find, FirstOrDefault, etc.
However I am unsure how to accomplish anymore than the SaveChanges/SaveChangesAsync as they are easily overrideable in my DbContext class.
You can try using EF6 logging - https://msdn.microsoft.com/en-us/data/dn469464.aspx.
Related
Suppose you have a Schema that is used in a UI-App (e.g. Vue), a Node.js or Springboot Server and has to validate against Databases (e.g. SQL, mongoDB,...), and maybe some Micro-services running on whatever.
How and where do I manage a this JSON-Schema, so that if I have to change the schema for whatever Reason, that every architectural component can handle the new JSON-Schema(s).
Otherwise I need to update the Schema in up to 10 projects so none is incompatible.
Is it really as simple as having a git project full with just JSON-Schemas or do I need specific loaders for each language/environment?
Are there best practices that I am unaware of?
PS: I don't really think I need the automatically synchronized on runtime, so don't really think I need another Microservice to achieve that.
That being said, if a Microservice is the best way to go, then getting a Microservice it is.
If you keep them in a git project, how do you load them? Clone the project each time the app starts? It may work, but I would go with a more flexible approach that should take too much effort to be done:
Build a JSON schema repository accessible via a REST API
When the app starts, it makes a request to grab the schema (latest, or a specific version)
That way you get an uniform (and scalable) way of playing with the schemas. Even if you think about a hot-reload sometime in the future, you can leverage this approach to do that.
Here is an old project in this direction, you may give it a shot to see if it works (or for some inspiration, at least)
I get the Error Unable to load DLL 'sqlite3' while I have the XAML Designer of my WP8.1 Universal project open and a Data Context set like this:
DataContext="{Binding IntakeReasonListViewModel, Source={StaticResource Locator}}"
The Locator is designed like the recommended MVVM Light View Model Locator and uses the ServiceLocator.
The error message appears only in design time and it works withouth any problems while executing. Also I have 3 apps. 2 of them have this issue, one does not. But I can't find any difference between them regarding to the SQLite.
I found different threads with the similar message, but all these problems appeard to runtime and caused some errors on saving items, while mine problem doesn't.
EDIT: I found out that the problem is that I inject my data access via a repository class to the view model. This way the designer tries to load the data access, inclusive the sqlite modul..
Does anyone know a way to avoid this for design time?
Thanks
Regards
NPadrutt
You can always use a separate ViewModel for design time. I find it a good practice to have 3 files for each View (eg. for MainPage):
IMainPageViewModel (contains bindable properties, commands etc...)
MainPageViewModel (child of ViewModelBase, implements IMainPageViewModel)
MainPageDesignViewModel (child of ViewModelBase, implements IMainPageViewModel)
This way you can avoid loading the other services, and just display some demo data that'll help you in design mode. This answer to an other question details how to use a separate service or a separate ViewModel for design time: https://stackoverflow.com/a/14154088/4788286 (With MVVMLight the key is to use the ViewModelBase.IsInDesignMode and ViewModelBase.IsInDesignModeStatic properties.)
I was told in a previous question that there can be issues when using db4o server without persistent classes. On the Versant web site, they just say that native queries won't be available.
So what are the issues possible in this particular configuration, except less features ?
Some features do not work:
All query methods except SODA queries do not work.
Some type of objects my create issues like enums etc.
The main concern is just the 'stability' and 'matureness' of this feature. db4o hasn't been design to work without the classes available. The test-suite and feature design is centered around scenarios with classes available.
Or from the internal implementation standpoint: The 'generic'-reflection layer is very brittle. That's the component which is required for this feature.
Well if up for taking a risk and only use SODA as query engine you can try it. However if you rather do not run into bugs / limitations than avoid it.
After reading the nice answers in this question, I watched the screencasts by Justin Etheredge. It all seems very nice, with a minimum of setup you get DI right from your code.
Now the question that creeps up to me is: why would you want to use a DI framework that doesn't use configuration files? Isn't that the whole point of using a DI infrastructure so that you can alter the behaviour (the "strategy", so to speak) after building/releasing/whatever the code?
Can anyone give me a good use case that validates using a non-configured DI like Ninject?
I don't think you want a DI-framework without configuration. I think you want a DI-framework with the configuration you need.
I'll take spring as an example. Back in the "old days" we used to put everything in XML files to make everything configurable.
When switching to fully annotated regime you basically define which component roles yor application contains. So a given
service may for instance have one implementation which is for "regular runtime" where there is another implementation that belongs
in the "Stubbed" version of the application. Furthermore, when wiring for integration tests you may be using a third implementation.
When looking at the problem this way you quickly realize that most applications only contain a very limited set of component roles
in the runtime - these are the things that actually cause different versions of a component to be used. And usually a given implementation of a component is always bound to this role; it is really the reason-of-existence of that implementation.
So if you let the "configuration" simply specify which component roles you require, you can get away without much more configuration at all.
Of course, there's always going to be exceptions, but then you just handle the exceptions instead.
I'm on a path with krosenvold, here, only with less text: Within most applications, you have a exactly one implementation per required "service". We simply don't write applications where each object needs 10 or more implementations of each service. So it would make sense to have a simple way say "this is the default implementation, 99% of all objects using this service will be happy with it".
In tests, you usually use a specific mockup, so no need for any config there either (since you do the wiring manually).
This is what convention-over-configuration is all about. Most of the time, the configuration is simply a dump repeating of something that the DI framework should know already :)
In my apps, I use the class object as the key to look up implementations and the "key" happens to be the default implementation. If my DI framework can't find an override in the config, it will just try to instantiate the key. With over 1000 "services", I need four overrides. That would be a lot of useless XML to write.
With dependency injection unit tests become very simple to set up, because you can inject mocks instead of real objects in your object under test. You don't need configuration for that, just create and injects the mocks in the unit test code.
I received this comment on my blog, from Nate Kohari:
Glad you're considering using Ninject!
Ninject takes the stance that the
configuration of your DI framework is
actually part of your application, and
shouldn't be publicly configurable. If
you want certain bindings to be
configurable, you can easily make your
Ninject modules read your app.config.
Having your bindings in code saves you
from the verbosity of XML, and gives
you type-safety, refactorability, and
intellisense.
you don't even need to use a DI framework to apply the dependency injection pattern. you can simply make use of static factory methods for creating your objects, if you don't need configurability apart from recompiling code.
so it all depends on how configurable you want your application to be. if you want it to be configurable/pluggable without code recompilation, you'll want something you can configure via text or xml files.
I'll second the use of DI for testing. I only really consider using DI at the moment for testing, as our application doesn't require any configuration-based flexibility - it's also far too large to consider at the moment.
DI tends to lead to cleaner, more separated design - and that gives advantages all round.
If you want to change the behavior after a release build, then you will need a DI framework that supports external configurations, yes.
But I can think of other scenarios in which this configuration isn't necessary: for example control the injection of the components in your business logic. Or use a DI framework to make unit testing easier.
You should read about PRISM in .NET (it's best practices to do composite applications in .NET). In these best practices each module "Expose" their implementation type inside a shared container. This way each module has clear responsabilities over "who provide the implementation for this interface". I think it will be clear enough when you will understand how PRISM work.
When you use inversion of control you are helping to make your class do as little as possible. Let's say you have some windows service that waits for files and then performs a series of processes on the file. One of the processes is to convert it to ZIP it then Email it.
public class ZipProcessor : IFileProcessor
{
IZipService ZipService;
IEmailService EmailService;
public void Process(string fileName)
{
ZipService.Zip(fileName, Path.ChangeFileExtension(fileName, ".zip"));
EmailService.SendEmailTo(................);
}
}
Why would this class need to actually do the zipping and the emailing when you could have dedicated classes to do this for you? Obviously you wouldn't, but that's only a lead up to my point :-)
In addition to not implementing the Zip and email why should the class know which class implements the service? If you pass interfaces to the constructor of this processor then it never needs to create an instance of a specific class, it is given everything it needs to do the job.
Using a D.I.C. you can configure which classes implement certain interfaces and then just get it to create an instance for you, it will inject the dependencies into the class.
var processor = Container.Resolve<ZipProcessor>();
So now not only have you cleanly separated the class's functionality from shared functionality, but you have also prevented the consumer/provider from having any explicit knowledge of each other. This makes reading code easier to understand because there are less factors to consider at the same time.
Finally, when unit testing you can pass in mocked dependencies. When you test your ZipProcessor your mocked services will merely assert that the class attempted to send an email rather than it really trying to send one.
//Mock the ZIP
var mockZipService = MockRepository.GenerateMock<IZipService>();
mockZipService.Expect(x => x.Zip("Hello.xml", "Hello.zip"));
//Mock the email send
var mockEmailService = MockRepository.GenerateMock<IEmailService>();
mockEmailService.Expect(x => x.SendEmailTo(.................);
//Test the processor
var testSubject = new ZipProcessor(mockZipService, mockEmailService);
testSubject.Process("Hello.xml");
//Assert it used the services in the correct way
mockZipService.VerifyAlLExpectations();
mockEmailService.VerifyAllExceptions();
So in short. You would want to do it to
01: Prevent consumers from knowing explicitly which provider implements the services it needs, which means there's less to understand at once when you read code.
02: Make unit testing easier.
Pete
In all my projects till now, I use to use singleton pattern to access Application configuration throughout the application. Lately I see lot of articles taking about not to use singleton pattern , because this pattern does not promote of testability also it hides the Component dependency.
My question is what is the best way to store Application configuration, which is easily accessible throughout the application without passing the configuration object all over the application ?.
Thanks in Advance
Madhu
I think an application configuration is an excellent use of the Singleton pattern. I tend to use it myself to prevent having to reread the configuration each time I want to access it and because I like to have the configuration be strongly typed (i.e, not have to convert non-string values each time). I usually build in some backdoor methods to my Singleton to support testability -- i.e., the ability to inject an XML configuration so I can set it in my test and the ability to destroy the Singleton so that it gets recreated when needed. Typically these are private methods that I access via reflection so that they are hidden from the public interface.
EDIT We live and learn. While I think application configuration is one of the few places to use a Singleton, I don't do this any more. Typically, now, I will create an interface and a standard class implementation using static, Lazy<T> backing fields for the configuration properties. This allows me to have the "initialize once" behavior for each property with a better design for testability.
Use dependency injection to inject the single configuration object into any classes that need it. This way you can use a mock configuration for testing or whatever you want... you're not explicitly going out and getting something that needs to be initialized with configuration files. With dependency injection, you are not passing the object around either.
For that specific situation I would create one configuration object and pass it around to those who need it.
Since it is the configuration it should be used only in certain parts of the app and not necessarily should be Omnipresent.
However if you haven't had problems using them, and don't want to test it that hard, you should keep going as you did until today.
Read the discussion about why are they considered harmful. I think most of the problems come when a lot of resources are being held by the singleton.
For the app configuration I think it would be safe to keep it like it is.
The singleton pattern seems to be the way to go. Here's a Setting class that I wrote that works well for me.
If any component relies on configuration that can be changed at runtime (for example theme support for widgets), you need to provide some callback or signaling mechanism to notify about the changed config. That's why it is not enough to pass only the needed parameters to the component at creation time (like color).
You also need to provide access to the config from inside of the component (pass complete config to component), or make a component factory that stores references to the config and all its created components so it can eventually apply the changes.
The former has the big downside that it clutters the constructors or blows up the interface, though it is maybe fastest for prototyping. If you take the "Law of Demeter" into account this is a big no because it violates encapsulation.
The latter has the advantage that components keep their specific interface where components only take what they need, and as a bonus gives you a central place for refactoring (the factory). In the long run code maintenance will likely benefit from the factory pattern.
Also, even if the factory was a singleton, it would likely be used in far fewer places than a configuration singleton would have been.
Here is an example done using Castale.Core >> DictionaryAdapter and StructureMap