How to specify EntityFramework ProviderName in an Azure Function

Question

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..

Answer 1

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.

1. 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.

2. 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.

3. 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

4. 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());
            }
        }
    }

5. 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:
}

Answer 2

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