I am trying to implement dependency injection for the first time in my new project in .Net MAUI. For testing purposes, I want to fetch data from a local source in my ViewModel. The production scenario will fetch data from the remote data source using HttpClient.
Below is my code base structure:
I have an Interface:
public interface IApiService
{
Task<bool> GetSomething(string parameter);
Task<string> GetSomethingElse(string parameter);
}
I have two classes that derive from it.
public class LocalDataStore: IApiService
public class RemoteDataStore: IApiService
In my MauiProgram.cs, when I want to use Local Data Store:
builder.Services.AddSingleton<LocalDataStore>()
builder.Services.AddSingleton<IApiService>()
And for Remote Data Store
builder.Services.AddSingleton<RemoteDataStore>()
builder.Services.AddSingleton<IApiService>()
In my ViewModel:
public class Page1ViewModel
{
public Page1ViewModel(IApiService localDataStore)
{
var items = Task.Run(async () => await localDataStore.GetSomething(true));
}
}
While running the app, I get an error :
System.InvalidOperationException: 'Unable to resolve service for type '...IApiService' while attempting to activate 'ViewModels.Page1ViewModel'.'
What am I doing wrong or what else should I be doing?
Kindly help.
Thanks, and regards.
Edit*
Of course, it works if I use LocalDataStore or RemoteDataStore instead of IApiService, when I register the services with the builder. But then if I have to change from one data store to another, I will have to change that in all the ViewModel classes?
It was trivial.
I needed to register the service like so :
builder.Services.AddSingleton<IApiService,LocalDataStore>();
Thanks to https://youtu.be/paZNvvUNFi0, I realised that.
Hope this helps someone.
I recently read THIS post on "Implementing database per tenant strategy" by G Pelpman.
It deals with connecting to multiple databases and uses a tenant to create a connection string.
The part I am confused about and what it allows is the following registering of services.
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<MultitenantDbContext>(o => { });
services.AddMvc();
services.AddTransient<ITenantProvider, DummyTenantProvider>();
}
In particular,
services.AddDbContext<MultitenantDbContext>(o => { });
Whats the reason for using (o => { });?
How does it help in connecting to multiple databases?
services.AddDbContext receives an Action (Action) as a parameter...
in this case, as said in the very post you shared "Implementing database per tenant strategy", no conections will be provided by ConfigureServices(), so an empty Action is passed to services.AddDbContext() to fullfil the optionsAction param...
Connections will be further provided based on the Tenant defined on DbContextOptionsBuilder._tenant
How I can get IContainer instance for my ASP.Net 5 app?
I need to enable diagnostics, and based on official documentation SubscribeToDiagnostics method is accessible only from IContainer, and ASP Net Core 3+ Integration this.AutofacContainer = app.ApplicationServices.GetAutofacRoot(); exposes only ILifetimeScope.
I have also noticed that Autofac supports DiagnosticListener - is this a way how I should trace for informations?
Does Autofac provide build in formatters for example for RequestDiagnosticData?
What are your recommendations?
I've updated the ASP.NET Core 3 example for Autofac to show how this works. The secret is using a build callback.
In your ConfigureContainer method, you register a callback to subscribe to diagnostics.
public void ConfigureContainer(ContainerBuilder builder)
{
// Add any Autofac modules or registrations, then...
//
// If you want to enable diagnostics, you can do that via a build
// callback. Diagnostics aren't free, so you shouldn't just do this
// by default. Note: since you're diagnosing the container you can't
// ALSO resolve the logger to which the diagnostics get written, so
// writing directly to the log destination is the way to go.
var tracer = new DefaultDiagnosticTracer();
tracer.OperationCompleted += (sender, args) =>
{
Console.WriteLine(args.TraceContent);
};
builder.RegisterBuildCallback(c =>
{
var container = c as IContainer;
container.SubscribeToDiagnostics(tracer);
});
}
I have a web project which is configured to provide an OData v 4.0 endpoint and is using the following components:
ASP.NET Web Api 5.2.2
Entity Framework 6.1.1
Owin 5.2.2
OData 5.3.1
The entire web application is using Windsor container from Castle Project.
The lifestyle of my controllers is per web request and same applies for all dependencies including DbContext.
The IoC is configured as following:
Owin Startup .cs
WindsorConfig.InitializeContainer(GlobalConfiguration.Configuration);
Configuration.cs
IWindsorContainer container = new WindsorContainer();
container.Install(FromAssembly.This());
container.Register(Component.For<IWindsorContainer>().Instance(container));
config.DependencyResolver = new WindsorDependencyResolver(container);
Installer.cs
container.Register(FromAssembly.This()
.BasedOn<ODataController>()
.LifestylePerWebRequest());
container.Register(
Component
.For<DbContext>()
.ImplementedBy<MyContext>()
.LifestylePerWebRequest());
So, an OData controller looks like this:
public class PersonsController : ODataController
{
#region Public Constructors
public PersonsController(ICommandDispatcher commandDispatcher, DbContext session)
{
this.commandDispatcher = commandDispatcher;
this.session = session;
}
public IQueryable<Person> Get()
{
return session
.Set<Person>()
.AsNoTracking();
}
public SingleResult<Person> Get([FromODataUri] Guid key)
{
return SingleResult.Create(session
.Set<Person>()
.AsNoTracking()
.Where(x => x.Id == key));
}
}
I am using Set.AsNoTracking() to avoid extra memory usage from Entity Framework.
Anyway, during time, after 100/150 queries the memory of the app pool keep raising of 1-2 MB and it never gets recycled.
Am I doing something wrong? Maybe Castle is not appropriate for this project and I have to use another IoC container?
I'm trying to port some webjob code to the new Azure Functions. So far I've managed to import my DLL's and reference them succesfully, but when I use the connection string in my code, I get an error saying I have to add the ProviderName:
The connection string 'ConnectionString' in the application's
configuration file does not contain the required providerName
attribute."
Which is normally not a problem because in a webjob (or web app), this will be in the App or Web.config, and the connectionstring will simply be overwritten with whatever I entered in Azure.
With Azure Functions, I don't have a web.config (Although I tried adding one to no avail), so naturally the providername is missing.
How do I specify that?
EDIT:
After some playing around and some helpful tips by people below, I've almost managed to get it working.
What I do now is the following:
var connString = **MY CONN STRING FROM CONFIG**; // Constring without metadata etc.
EntityConnectionStringBuilder b = new EntityConnectionStringBuilder();
b.Metadata = "res://*/Entities.MyDB.csdl|res://*/Entities.MyDB.ssdl|res://*/Entities.MyDB.msl";
b.ProviderConnectionString = connString.ConnectionString;
b.Provider = "System.Data.SqlClient";
return new MyDB(b.ConnectionString);
Which gives me what I need for calling the database. I use a static method in a partial class to get an instance of the Database which runs the above code, and I decorate my MyDB Partial with [DbConfigurationType(typeof(MyDbConfiguration))]
I define that configuration as:
public class MyDBConfiguration: DbConfiguration
{
public MyDBConfiguration()
{
SetProviderFactory("System.Data.EntityClient", EntityProviderFactory.Instance);
}
}
My problem remains when I want to actually use the EF Entities. Here, it will try to initialize the database type using the original configuration, giving me the original error once again. As per this stack trace:
at Void Initialize()
at System.Data.Entity.Internal.EntitySetTypePair GetEntitySetAndBaseTypeForType(System.Type)
at Void InitializeContext()
at System.Data.Entity.Core.Objects.ObjectContext CreateObjectContextFromConnectionModel()
at Void Initialize()
at Boolean TryInitializeFromAppConfig(System.String, System.Data.Entity.Internal.AppConfig)
at Void InitializeFromConnectionStringSetting(System.Configuration.ConnectionStringSettings)
So how do I avoid this? I guess I need a way to hook into everything and run my custom setter..
In the end, Stephen Reindel pushed me in the right direction; Code-based Configuration for Entity Framework.
[DbConfigurationType(typeof(MyDBConfiguration))]
public partial class MyDB
{
public static MyDB GetDB()
{
var connString = **MY CONN STRING FROM SOMEWHERE**; // Constring without metadata etc.
EntityConnectionStringBuilder b = new EntityConnectionStringBuilder();
b.Metadata = "res://*/Entities.MyDB.csdl|res://*/Entities.MyDB.ssdl|res://*/Entities.MyDB.msl";
b.ProviderConnectionString = connString.ConnectionString;
b.Provider = "System.Data.SqlClient";
return new MyDB(b.ConnectionString);
}
public MyDB(string connectionString) : base(connectionString)
{
}
}
With MyDbConfiguration like this:
public class MyDBConfiguration: DbConfiguration
{
public MyDBConfiguration()
{
SetProviderServices("System.Data.SqlClient", SqlProviderServices.Instance);
SetDefaultConnectionFactory(new SqlConnectionFactory());
}
}
With the above code, EF never asks for AppConfig-related config files. But remember, if you have EF entries in your config file, it will attempt to use them, so make sure they're gone.
In terms of azure functions, this means I used the Azure Functions configuration panel in azure to punch in my ConnectionString without the Metadata and providername, and then loaded that in GetDB.
Edit: As per request, here is some explanatory text of the above:
You can't add EF metadata about the connection in Azure Functions, as they do not use an app.config in which to specify it. This is not a part of the connection string, but is metadata about the connection besides the connection string that EF uses to map to a specific C# Class and SQL Provider etc. To avoid this, you hardcode it using the above example. You do that by creating a class inheriting from DBConfiguration, and you mark (with an attribute on a partial class) your EF database class with that.
This DBConfiguration contains a different kind of way to instantiate a new database object, in which this metadata is hardcoded, but the connectionstring is retrieved from your app settings in Azure. In this example I just used a static method, but I guess it could be a new constructor also.
Once you have this static method in play, you can use that to get a new database in your database code, like this:
using (var db = MyDB.GetDB()) {
// db code here.
}
This allows you to use EntityFramework without an APP.Config, and you can still change the connectionstring using Azure Functions APP settings.
Hope that helps
Using this question you can set your default factory before opening the connection by having your personal DbConfiguration class (see this link also for usage):
public class MyDbConfiguration : DbConfiguration
{
public MyDbConfiguration()
{
SetDefaultConnectionFactory(new SqlConnectionFactory());
}
}
Now you need to tell your DbContext to use the new configuration. As using web.config or app.config is no option, you may use an attribute to add the configuration:
[DbConfigurationType(typeof(MyDbConfiguration))]
public class MyContextContext : DbContext
{
}
Now using a connection string on your DbContext will use the SQL provider by default.
Provided answer is perfect and it helped me a lot but it is not dynamic as I dont want to hardcode my connectionstring. if you are working the slots in azure functions. I was looking for a solution where I can use more than 1 connection strings. Here is my alternative approach step by step for anybody else struggling with this problem.
most important thing is that we understand local.settings.json file
IS NOT FOR AZURE. it is to run your app in the local as the name is
clearly saying. So solution is nothing to do with this file.
App.Config or Web.Config doesnt work for Azure function connection strings. If you have Database Layer Library you cant overwrite connection string using any of these as you would do in Asp.Net applications.
In order to work with, you need to define your connection string on the azure portal under the Application Settings in your Azure function. There is
Connection strings. there you should copy your connection string of your DBContext. if it is edmx, it will look like as below. There is Connection type, I use it SQlAzure but I tested with Custom(somebody claimed only works with custom) works with both.
metadata=res:///Models.myDB.csdl|res:///Models.myDB.ssdl|res://*/Models.myDB.msl;provider=System.Data.SqlClient;provider
connection string='data source=[yourdbURL];initial
catalog=myDB;persist security info=True;user
id=xxxx;password=xxx;MultipleActiveResultSets=True;App=EntityFramework
After you set this up, You need to read the url in your application and provide the DBContext. DbContext implements a constructor with connection string parameter. By default constructor is without any parameter but you can extend this. if you are using POCO class, you can amend DbContext class simply. If you use Database generated Edmx classes like me, you dont want to touch the auto generated edmx class instead of you want to create partial class in the same namespace and extend this class as below.
This is auto generated DbContext
namespace myApp.Data.Models
{
public partial class myDBEntities : DbContext
{
public myDBEntities()
: base("name=myDBEntities")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
}
this is the new partial class, you create
namespace myApp.Data.Models
{
[DbConfigurationType(typeof(myDBContextConfig))]
partial class myDBEntities
{
public myDBEntities(string connectionString) : base(connectionString)
{
}
}
public class myDBContextConfig : DbConfiguration
{
public myDBContextConfig()
{
SetProviderServices("System.Data.EntityClient",
SqlProviderServices.Instance);
SetDefaultConnectionFactory(new SqlConnectionFactory());
}
}
}
After all you can get the connection string from azure settings, in your Azure Function project with the code below and provide to your DbContext
myDBEntities is the name you gave in the azure portal for your connection string.
var connString = ConfigurationManager.ConnectionStrings["myDBEntities"].ConnectionString;
using (var dbContext = new myDBEntities(connString))
{
//TODO:
}
Adding an answer in the event you cannot simply change the way you instantiate you DbContext. This would occur if you are calling code that has DbContexts being instatiated with the parameter-less constructor.
It involves using a static constructor to read your connection string from the appsettings in the azure portal and passing it in to your DbContext base constructor. This allows you to circumvent the need for a providerName and also allows you to retain use of the portal configuration without needing to hardcode anything.
Please refer to my accepted answer here: Missing ProviderName when debugging AzureFunction as well as deploying azure function
Stumbled upon this and solved it like this, inside of the Azure Function.
public static class MyFunction
{
// Putting this in more than one place in your project will cause an exception,
// if doing it after the DbConfiguration has been loaded.
static MyFunction() =>
DbConfiguration.Loaded += (_, d) =>
d.AddDefaultResolver(new global::MySql.Data.Entity.MySqlDependencyResolver());
// The rest of your function...
//[FunctionName("MyFunction")]
//public static async Task Run() {}
}
You can access the site's App Settings by going to the portal, clicking Function app settings and then Configure app settings. That will open up a blade that allows you to set all the app settings for your function app. Just use the same key and value that you'd use for your web.config.