I am new to ILOG and I want to know, what does this statement mean:
IlrContext() from ?context;
I do not see "context" defined as variable in a sample project in my work space. Is this an implicit variable that is defined in ILOG?
IlrContext is the base class of all the execution contexts. Rules can be executed only within an execution context.
An IlrContext instance provide all context data to the engine (rulesets, variables, parameters etc.)
IlrContext Class
Related
How DbMigrator works
I have code that instantiates a new DbMigrator(new Configuration())
Configuration is a custom extension of DbMigrationsConfiguration<T>, where T is DbContext
So within Configuration, there is a ContextType, which is equal to <T>.
When DbMigrator is instantiated, it attempts to create an instance of the <T> DbContext. It will either try to use an Empty Constructor on the <T> Context, or it will attempt to look for an implementation of IDbContextFactory<...> where ... is the actual type of , but not generic T.
How DbMigrator Doesn't Work
The problem is, the assembly instantiating DbMigrator has no access to the specific typed IDbContextFactory<...> that it needs to discover. Also, my DbContext has no default constructor, and I don't want it to. So I receive the exception The target context '...' is not constructible.
The thing that bothers me is, at the point I am instantiating DbMigrator, I already have an instance (or may already be within an instance) of the DbContext I am migrating. Also, I have access to a generic IDbContextFactory<T> that is not discoverable by DbMigrator's internals, but I'd be happy to provide it an instance.
The Question
So how do I tell DbMigrator to either just use my Context instance, or use an instance of a IDbContextFactory I specify? When it relies on its magic juju behind the scenes to try to discover these things (presumably using reflection/ServiceLocation) it is failing.
My Situation
Within one AppDomain, I am using n Contexts. I'd like to say one, but it's typically two, and may be more than that. So any solution that relies on a single app/web config property, or an attribute decorator, which points to a single DbConfiguration or ConnectionFactory won't work for me. Because there can only be one per AppDomain and, unless I could configure it based contextually on which Context I'm needing at the time, it is futile. So there's wiggle room there, but I dunno.
Also, there may be some juju I don't understand about EF relating to the base constructor. But I don't believe passing a DbConnection into the constructor instead of a nameOrConnectionString would work. It is still not an empty constructor. But if there's something EF does to search for constructors with that, and how to utilize it, that MIGHT work.
I am new to dependency injection pattern. I love the idea, but struggle to apply it to my case. I have a singleton object, let’s call it X, which I need often in many parts of my program, in many different classes, sometimes deep in the call stack. Usually I would implement this as a globally available singleton. How is this implemented within the DI pattern, specifically with .NET Core DI container? I understand I need to register X with the DI container as a singleton, but how then I get access to it? DI will instantiate classes with constructors which will take reference to X, that’s great – but I need X deep within the call hierarchy, within my own objects which .NET Core or DI container know nothing about, in objects that were created using new rather than instantiated by the DI container.
I guess my question is – how does global singleton pattern aligns/implemented by/replaced by/avoided with the DI pattern?
Well, "new is glue" (Link). That means if you have new'ed an instance, it is glued to your implementation. You cannot easily exchange it with a different implementation, for example a mock for testing. Like gluing together Lego bricks.
I you want to use proper dependency injection (using a container/framework or not) you need to structure your program in a way that you don't glue your components together, but instead inject them.
Every class is basically at hierarchy level 1 then. You need an instance of your logger? You inject it. You need an instance of a class that needs a logger? You inject it. You want to test your logging mechanism? Easy, you just inject something that conforms to your logger interface that logs into a list and the at the end of your test you can check your list and see if all the required logs are there. That is something you can automate (in contrast to using your normal logging mechanism and checking the logfiles by hand).
That means in the end, you don't really have a hierarchy, because every class you have just gets their dependencies injected and it will be the container/framework or your controlling code that determines what that means for the order of instantiation of objects.
As far as design patterns go, allow me an observation: even now, you don't need a singleton. Right now in your program, it would work if you had a plain global variable. But I guess you read that global variables are "bad". And design patterns are "good". And since you need a global variable and singleton delivers a global variable, why use the "bad", when you can use the "good" right? Well, the problem is, even with a singleton, the global variable is bad. It's a drawback of the pattern, a toad you have to swallow for the singleton logic to work. In your case, you don't need the singleton logic, but you like the taste of toads. So you created a singleton. Don't do that with design patterns. Read them very carefully and make sure you use them for the intended purpose, not because you like their side-effects or because it feels good to use a design pattern.
Just an idea and maybe I need your thought:
public static class DependencyResolver
{
public static Func<IServiceProvider> GetServiceProvider;
}
Then in Startup:
public void Configure(IApplicationBuilder app, IServiceProvider serviceProvider)
{
DependencyResolver.GetServiceProvider = () => { return serviceProvider; };
}
And now in any deed class:
DependencyResolver.GetServiceProvider().GetService<IService>();
Here's a simplified example of how this would work without a singleton.
This example assumes that your project is built in the following way:
the entry point is main
main creates an instance of class GuiCreator, then calls the method createAndRunGUI()
everything else is handled by that method
So your simplified code looks like this:
// main
// ... (boilerplate)
container = new Container();
gui = new GuiCreator(container.getDatabase(), container.getLogger(), container.getOtherDependency());
gui.createAndRunGUI();
// ... (boilerplate)
// GuiCreator
public class GuiCreator {
private IDatabase db;
private ILogger log;
private IOtherDependency other;
public GuiCreator(IDatabase newdb, ILogger newlog, IOtherDependency newother) {
db = newdb;
log = newlog;
other = newother;
}
public void createAndRunGUI() {
// do stuff
}
}
The Container class is where you actually define which implementations will be used, while the GuiCreator contructor takes interfaces as arguments. Now let's say the implementation of ILogger you choose has itself a dependency, defined by an interface its contructor takes as argument. The Container knows this and resolves it accordingly by instantiating the Logger as new LoggerImplementation(getLoggerDependency());. This goes on for the entire dependency chain.
So in essence:
All classes keep instances of interfaces they depend upon as members.
These members are set in the respective constructor.
The entire dependency chain is thus resolved when the first object is instantiated. Note that there might/should be some lazy loading involved here.
The only places where the container's methods are accessed to create instances are in main and inside the container itself:
Any class used in main receives its dependencies from main's container instance.
Any class not used in main, but rather used only as a dependency, is instantiated by the container and receives its dependencies from within there.
Any class used neither in main nor indirectly as a dependency somewhere below the classes used in main will obviously never be instantiated.
Thus, no class actually needs a reference to the container. In fact, no class needs to know there even is a container in your project. All they know is which interfaces they personally need.
The Container can either be provided by some third party library/framework or you can code it yourself. Typically, it will use some configuration file to determine which implementations are actually supposed to be used for the various interfaces. Third party containers will usually perform some sort of code analysis supported by annotations to "autowire" implementations, so if you go with a ready-made tool, make sure you read up on how that part works because it will generally make your life easier down the road.
I have been using FeatureContext for storing information about a specific feature that can be reused in all scenarios in that feature. However I have some things like login information that I don't want to recreate for every feature. I want to use the [BeforeTestRun] attribute to store this, but does SpecFlow have some sort of Global Context feature (like log4net) to store this information so it can be reused by all features?
SpecFlow doesnt have a global context construct, however you have a few options that can help you share data between bindings/features:
Static members
You can use static field/property to set objects that can be used across all features during test execution. Keep thread safety in mind however, because if you run your tests in parallel you need to synchronize initialisation and any mutable access to this field. If you want this data to change per scenario you can set the object in the context when accessed, this way you can set a default, and allow the scenario to have its own copy.
Context injection
You can use SpecFlow Context injection to inject a object into step definitions via the constructor, this way you can initialize your type using its default constructor and the pass the type into the step def like so:
[Binding]
public class MyStepDefinition
{
private readonly MyContextData contextData;
public MyStepDefinition(MyContextData contextData)
{
this.contextData = contextData;
}
}
more info:
https://github.com/techtalk/SpecFlow/wiki/Sharing-Data-between-Bindings
When a class that contains code is instantiated, is the code is the class shared automatically by other instantiations of that same class? Eg. The data in the class that is instantiated may be minimal; however the code could be very significant. If the code is not "automatically" shared, is there a way to achieve that other than separating the code from the class data?
Sure.
Classes have the state and the behavior.
The state is encoded in member variables of the class. Each instance has its own copy of variables, thus its own state.
The behavior is specified by the methods implemented in the class ('methods' here stand for all static, non-static methods, setters and getters). Implementation is shared by all instances of the class, so all instances behave the same, but actual results and side-effects depend on instance state, obviously.
I have simple win service, that executes few tasks periodically. How should I pass Ninject kernel to all my task classes?
Is it good idea to create static variable of base task class and initialize it on service start?
Rather than a static variable on the base task class, I would favor injecting the kernel into each class instance. This provides a bit more flexibility should you ever decide that you need more than one kernel (for whatever reason). The static variable in the base class just seems yucky, for lack of a better term.