Missing ProviderName when debugging AzureFunction

问题:

I have an issue getting a DbContext to correctly pull my connection string from my local.settings.json

Context:

• This is an Azure function project
• The main problem code is in System.Data.Entity.Internal.AppConfig
• Although I have a local.settings.json file this is not dotnet core. It's .net 4.6.1

Error message:

'The connection string 'ShipBob_DevEntities' in the application's configuration file does not contain the required providerName attribute."'

Json configuration:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "",
    "AzureWebJobsDashboard": ""
},

"ConnectionStrings": {
"ShipBob_DevEntities": {
  "ConnectionString": "metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;provider=System.Data.SqlClient;provider connection string='data source=***;initial catalog=***;persist security info=True;User Id=***;Password=***;;multipleactiveresultsets=True;application name=EntityFramework'",
  "providerName": "System.Data.EntityClient"
    }
  }
}  

Configuration versions tested:

• Moving the provider name into the actual ConnectionString token value : same error ocurrs
• Setting the provider attribute inside the ConnectionString attribute to EntityClient: this did nothing

• Making ShipBob_DevEntities a string value = to the value of ConnectionString : this throws new errors the likes of which are

  keyword metadata is not supported

• I tried using an ADO connection string which throws a code first exception which seems to occur when your connection string is incorrect in a database first approach.

I've taken the liberty to decompile EntityFramework.dll using dotPeek and have traced the problem down to System.Data.Entity.Internal.LazyInternalConnection.TryInitializeFromAppConfig. Inside this method there is a call to LazyInternalConnection.FindConnectionInConfig which spits out a ConnectionStringSettings object that has it's ProviderName value set to null. Unfortunately I am unable to debug the AppConfig.cs class which it seems to use to generate this value so I am stuck.

So far I have consulted these two articles. One of which states to put the provider name as it's own token; however, this is not working.

https://github.com/Azure/azure-functions-cli/issues/193
https://github.com/Azure/azure-functions-cli/issues/46

Does anyone know the correct format to use in local.settings.json for an Entity Framework connection?

回答1:

So the solution ended up being trivial. The ProviderName attribute specified in local.settings.json MUST be camel case.

From the original git hub discussions :
https://github.com/Azure/azure-functions-cli/issues/46
Shows the provider name as being pascal case

https://github.com/Azure/azure-functions-cli/issues/193
Shows the provider name being camel case in pseudo code It was very easy to miss but your config section must be exactly as follows

"ConnectionStrings": {
"ShipBob_DevEntities": {
  "ConnectionString": "metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;provider=System.Data.SqlClient;provider connection string='data source=***;initial catalog=***;persist security info=True;User Id=***;Password=***;;multipleactiveresultsets=True;application name=EntityFramework'",
  "ProviderName":  "System.Data.EntityClient"
  }
}  

These points are important:

• Make sure your connection string has metadata information
• If copying your string from an xml config, make sure you unescape apostrophes
• Make sure the ProviderName attribute is camel case
• Make sure the provider name is System.Data.EntityClient

Fix for missing providername in deployment

Note, this answer assumes you are trying to use the parameterless constructor of a DbContext. If you are creating new code you can easily follow the second upvoted answer

I figured out a way to circumvent the provider name issue while still retaining the use of the portal config and thus deployment slots. It involves setting the default connection string of db context using static properties

private static string _connectionString = "name=ShipBob_DevEntities";

    static ShipBob_DevEntities()
    {
        if(!string.IsNullOrEmpty(System.Environment.GetEnvironmentVariable("AzureFunction")))
        {
            var connectionString = System.Environment.GetEnvironmentVariable("EntityFrameworkConnectionString");

            if (!string.IsNullOrEmpty(connectionString))
            {
                _connectionString = connectionString;
            }
        }
    }

    public ShipBob_DevEntities()
        : base(_connectionString)
    {
        this.Configuration.LazyLoadingEnabled = false;
    }  

This involves the developer to create an app setting in the azure portal as a flag. In my case it is AzureFunction. This makes sure that our code is only run in an azure function and all other clients of this DbContext, whether they be web apps, windows apps, etc, can still continue behaving as expected. This also involves adding your connection string to the azure portal as an AppSetting and not an actual connection string. Please use the full connection string including them metadata information but without the provider name!

EDIT

You will need to edit your auto generated .tt file t4 template to make sure this code does not get overridden if you are using db first.

Here is a link on the T4 syntax: https://docs.microsoft.com/en-us/visualstudio/modeling/writing-a-t4-text-template

And here is an explanation on EF T4 templates: https://msdn.microsoft.com/en-us/library/jj613116(v=vs.113).aspx#1159a805-1bcf-4700-9e99-86d182f143fe

回答2:

I went through several similar questions and answers here. Many of them are either misleading or assuming everybody is on the same level and understands how the azure functions are working. there is no answer for newbies like me. I would like to summarize here my solution step by step. I dont think that provided answer is the best option because it forces you to change the auto generated edmx files which can be overwritten by mistake or next update of your edmx from database. Also best option here is to use Connection strings instead of App settings in my opinion.

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:
}

回答3:

I encountered the similar issue before, I would use the following approach for achieving my purpose, you could refer to it:

local.settings.json

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "DefaultEndpointsProtocol=https;AccountName=brucchstorage;AccountKey=<AccountKey>",
    "AzureWebJobsDashboard": "DefaultEndpointsProtocol=https;AccountName=brucchstorage;AccountKey=<AccountKey>",
    "sqldb-connectionstring": "Data Source=.\\sqlexpress;Initial Catalog=DefaultConnection;Integrated Security=True;Connect Timeout=15;Encrypt=False;TrustServerCertificate=True;ApplicationIntent=ReadWrite;MultiSubnetFailover=False"
  },
  "ConnectionStrings": {
    "Bruce_SQLConnectionString": "Data Source=.\\sqlexpress;Initial Catalog=DefaultConnection;Integrated Security=True;Connect Timeout=15;Encrypt=False;TrustServerCertificate=True;ApplicationIntent=ReadWrite;MultiSubnetFailover=False"
  }
} 

For retrieving the connection string:

var connString = ConfigurationManager.AppSettings["sqldb-connectionstring"];
//or var connString = ConfigurationManager.ConnectionStrings["Bruce_SQLConnectionString"].ConnectionString;
using (var dbContext = new BruceDbContext(connString))
{
    //TODO:
}

Or you could init your no-argument constructor for your DbContext as follows:

public class BruceDbContext:DbContext
{
    public BruceDbContext()
        : base("Bruce_SQLConnectionString")
    {
    }

    public BruceDbContext(string connectionString) : base(connectionString)
    {
    }
}

Then, you could create the instance for your DbContext as follows:

using (var dbContext = new BruceDbContext(connString))
{
    //TODO:
}

Moreover, you could refer to Local settings file for Azure Functions.