Issue with Entity Framework 6 while connecting to SQL Server from Azure function V2

问题

I am trying to use an existing library which is a .net library which uses EF 6.0 to connect to a database. Since Azure Functions does not have an app.config file, I am trying to set the connection string using C# code. But I am getting the following exception while connecting to the DB using my DB context:

System.ArgumentException: The ADO.NET provider with invariant name 'System.Data.SqlClient' is either not registered in the machine or application config file, or could not be loaded. See the inner exception for details.

System.ArgumentException: The specified invariant name 'System.Data.SqlClient' wasn't found in the list of registered .NET Data Providers

MyDBContext.partial.cs:

[DbConfigurationType(typeof(MyDbConfiguration))]
public partial class MyDBContext : DbContext
{
    public MyDBContext (string ConnectionString)
        : base(ConnectionString)
    {     
    }
}

public class MyDbConfiguration : DbConfiguration
{
    public MyDbConfiguration()
    {
        SetProviderServices("System.Data.SqlClient", SqlProviderServices.Instance);
        SetDefaultConnectionFactory(new SqlConnectionFactory());
    }
}

I have a method as following to get the DBContext. This method will be used by the library methods to get the DB context instance.

public MyDBContext GetDB( string metadata, string connectionString )
{
    EntityConnectionStringBuilder b = new EntityConnectionStringBuilder();
    b.Metadata = metadata;
    b.ProviderConnectionString = connectionString;
    b.Provider = "System.Data.SqlClient";
    return new MyDBContext (b.ConnectionString);
}

When I execute a library method to load data from db from an Azure function v2, which internally calls the above method to get DB Context and then connects to actual DB. Here MyDBContext object is getting created, but when it connects to db the following exception occurs.

System.ArgumentException: The ADO.NET provider with invariant name 'System.Data.SqlClient' is either not registered in the machine or application config file, or could not be loaded. See the inner exception for details.

System.ArgumentException: The specified invariant name 'System.Data.SqlClient' wasn't found in the list of registered .NET Data Providers

回答1:

I just worked on this issue but for Azure function V1. When using EF with Azure function, you can specify connection string in 'local.settings.json' file like this:

{
    "IsEncrypted": false,
    "Values": {
    "AzureWebJobsStorage": "",
    "AzureWebJobsDashboard": ""
    },
    "ConnectionStrings": {
        "YourEntities": {
            "ConnectionString":  "metadata=res://*/EF.yourModel.csdl|res://*/EF.yourModel.ssdl|res://*/EF.yourModel.msl;provider=System.Data.SqlClient;provider connection string='data source=yourServer;initial catalog=yourDB;persist security info=True;user id=yourUserID;password=yourPwd;MultipleActiveResultSets=True;App=EntityFramework'",
            "ProviderName": "System.Data.EntityClient"
        }
    }
}

Please pay attention to 'ProviderName' attribute. Case should be exact as shown above and provider should be 'EntityClient' Plus 'Provider Connection String' attribute of actual connection string should be in single quote (I am not sure why Microsoft did this but this is how it is supposed to be).

This will help you run your function app locally with EF without any more changes

Now for deployment in Azure. local.settings.json does not get deployed to cloud. As its name suggests it acts as configuration file for local run. So you need to set connection string in 'Configuration' of Azure function app on portal. There you can specify following parameters:

Name - 'YourEntities'
value - Just Connection string part from above json file
Type - 'Custom'
Slot Settings - according to your requirement

Now if you notice there is no way to specify ProviderName here. If you try to run function now you will get error for 'missing provider name'

Here your extended DBConfiguration class comes in handy.

Create your DB configuration class as below and specify provider as EntityType

public class YourDBContextConfig : DbConfiguration
{
    public YourDBContextConfig()
    {
    SetProviderServices("System.Data.EntityClient",
    SqlProviderServices.Instance);
    SetDefaultConnectionFactory(new SqlConnectionFactory());
    }

}

You can create this class in same file where you have created partial class for your DBContext

Add following attribute to your Context class: [DbConfigurationType(typeof(YourDBContextConfig))]

Also make sure your partial context class has constructor that takes connection string as parameter and supply it while initializing context:

string connString = 
ConfigurationManager.ConnectionStrings["YourEntities"].ConnectionString;
using (YourEntities db = new YourEntities(connString))
{
}

This will work for deployment.

来源：https://stackoverflow.com/questions/58084088/issue-with-entity-framework-6-while-connecting-to-sql-server-from-azure-function