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How can I add PostgreSQL to an existing Entity Framework 6 project while keeping the existing SQL Server provider intact?

Disclaimer: I'm a junior dev and still trying to wrap my head around EF6.
Our team has a .NET Framework 4.7 / Entity Framework 6 project which relies on MS SQL Server for its data. We just upgraded to Visual Studio 2022 but it seems like some of the recommended tools don't work on VS2022. We use database first for EF.
Recently, our team decided to add a create a new PostgreSQL database and we need to add support for it in our existing project.
I've installed the following packages:
Npgsql
EntityFramework6.Npgsql
I was advised to also install the following VS extension:
Npgsql PostgreSQL Integration
But it seems like it is only compatible up to VS2019 and has been abandoned.
In order to test if I could even set this up at all with the recommended VS extension, I used Visual Studio 2019 instead of 2022.
After installing the items listed above, my web.config file now has this entityFramework config:
<entityFramework>
<defaultConnectionFactory type="Npgsql.NpgsqlConnectionFactory, EntityFramework6.Npgsql" />
<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
<provider invariantName="Npgsql" type="Npgsql.NpgsqlServices, EntityFramework6.Npgsql" />
</providers>
</entityFramework>
and this system.data config:
<system.data>
<DbProviderFactories>
<remove invariant="Npgsql" />
<add name="Npgsql Provider" invariant="Npgsql" description=".NET Framework Data Provider for PostgreSQL" type="Npgsql.NpgsqlFactory, Npgsql, Version=4.1.3.0, Culture=neutral, PublicKeyToken=5d8b90d52f46fda7" />
</DbProviderFactories>
</system.data>
At this point, I attempted creating a new ADO.NET Entity Data Model, I was able to choose the table and procedure I wanted.
This is where I got stuck.
A new connectionString was added to my web.config, alongside the encrypted connectionString we were already using for SQL Server. When testing, it throws an exception saying that I cannot have an unencrypted connectionString next to an encrypted connectionString.
I tried placing the connectionString within the code but then it throws errors when parsing the connectionString, saying that it does not recognize the parameters. I used the same parameters from the connectionString that was automatically generated.
So, it seems like it's reading the Postgres connectionString with the SQL Server provider instead of the PostgreSQL provider.
Any suggestions? Or resources I can use to help me along the way? Thanks in advance.

Visual Studio 2017 not showing MySQL in connection list

I am using "Visual Studio 2017 Professional". I can not get a project to recognize that MySQL is an available DB option. MySQL does not show up in the list of possible connections when I create a new model. I know that there are tons of SO questions and other web pages on this topic because I have tried a lot of the suggestions. Each is subtlety different in cause and solution. None of the solutions seem to work for me.
I have tried the following with VS 2017 and 2015 with the same results. I have older versions of VS available but it didn't seem worthwhile to march that far back. I have also tried installing the latest and older versions of MySQL both with the "Community Installer" and the standalone msi's when necessary. I went back to the "latest" pre-6.10 version of MySQL.
To begin, this saga started last week when I noticed that nuget had MySQL package updates available. I applied them and then went to upgrade the installed MySQL componants with the Community Installer. The nuget changes did apply. The Community Installer could not uninstall MySQL for VS though. The system installer could not uninstall it. Rebooting and power-cycling did nothing.
On the advice of our local tech support folks I used a third party uninstaller that turned out to be more aggressive than we imagined. It seems to have randomly stommped across the registry erasing whatever it found. Long story short(er), I ended up having my machine reimaged. So, I have a fresh windows install.
Given the fresh Win10 platform, I installed the various things I normally use including the VS versions I typically use. I installed the latest Community MySQL installer. I did a "custom" MySQL install because I don't need a server on this device or fabric or many other things.
I finished the basic reinstall of everything then rebooted just to be sure. I started VS 2017 and created a new web app with the latest available version of .Net (4.6.1). I applied nuget updates and added EntityFramework and MySQL.Data. I then tried to create a new "code first" model.
I can get to the point where I am asked to create a connection. When I click the button the list of available DB providers only shows MS SQL.
I have seen the articles that say to add lines to Web.config and I have seen the MySQL .Net Connector docs that say the same things. I can see the MySQL entries in Web.config but they do not show up when creating a connection.
An oddity is that I can go to Tools -> Connect to Database and see EVERY DB type my machine knows about including MySQL. I can create the connection string and it works. I can see the DB in "Server Explorer` but that doesn't make it available to code.
Ok, I have followed the above steps over and over including downgrading the version of EntityFramework as well as the MySQL version.
My most recent attempt has me back to the latest version of VS and MySQL. The relevant (I think) section of the Web.config file follow. Note the defaultConnectionFactory entry is LocalDbConnectionFactory. I have changed that to SqlConnectionFactory but it has not made a difference. I have also changed the order of the providers and the order of the major blocks.
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
<parameters>
<parameter value="mssqllocaldb" />
</parameters>
</defaultConnectionFactory>
<providers>
<provider invariantName="System.Data.SqlClient"
type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
<provider invariantName="MySql.Data.MySqlClient"
type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.Entity.EF6, Version=6.10.6.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d">
</provider>
</providers>
</entityFramework>
<system.data>
<DbProviderFactories>
<remove invariant="MySql.Data.MySqlClient" />
<add description=".Net Framework Data Provider for MySQL" invariant="MySql.Data.MySqlClient"
name="MySQL Data Provider"
type="MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=6.10.6.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d" />
</DbProviderFactories>
</system.data>
Edit
My current impression is that VS 2017 is an unusable mess masquerading as a released, salable product. I have returned to 2015.
I have come closer to getting this to work in 2015. I have the latest MySQL items for VS and .Net installed. I have downgraded the nuget EF package to 6.0 and the MySql packages to 6.8.8.
In, what I am now calling, "the good old days" I could add a new model to an MVC project by selecting the Models folder; selecting "Add New Item"; choosing ADO.Net model; select a connection option (MySQL); enter the connection info; choose DB First or Code First and wait for the scaffolding fun to finish.
Now, I have to first go to Tools -> Connect to Database and create a conenction to a MySql DB. If I do not do this I will not see MySQL in the list of possible connections later. I then clean and build the project. Next i try to create the model as above. Noe I can see the MySQL connection option and I can enter the DB creds and test the connection.
The next step is to choose DB First or Code First. In either case, clicking the "next" button flashes a blank pop-up that then vanishes. No errors are shown and no connection is made.
It was never this hard in the past.
I have tried a lot of different MySQL and EF versions on 2015 and 2017 at this point. If there is a magic combo please tell me.

I have been fighting this fight for two weeks. I FINALLY found a combo of versions that works for me. The following was applied to a pristine re-image of my Win10 desktop two weeks ago. All patches were applied to system software before starting to deal with MySql.
Just this morning I re-read the post in this thread (MySql Forums): https://forums.mysql.com/read.php?174,659102,660369#msg-660369
I thought that I had tried those suggestions before but I must have messed up one of the versions. I think that poster's basic strategy is sound. In my case I uninstalled all local MySql parts and the installer.
I downloaded MySQL for Visual Studio - the Latest Development version (2.0.5 msi as of this writing) and installed that.
I found the OLD versions of the .Net Connector and installed 6.9.11
In VS 2017 I created a dummy project using .Net 4.6.1.
I applied pending VS updates.
I built the project.
I went to "Project -> Manage Nuget Packages" and installed / downgraded EntityFramework to 6.0.
I installed MySql.Data, MySql.Data.Entity and MySql.Web all at version 6.9.11
I cleaned and built the project then tried to add a new "Code First" model from a MySql DB... IT WORKED!

Thank you 7 Reeds for coming back with an answer. It led me to get it working, although I did it slightly differently.
In VS 2017 to connect to MySQL 5.6:
Uninstall any MySQL products from the machine
Set Target framework to .NET Framework 4.5.2
Uninstall EntityFramework and any MySQL packages in Nuget
Install MySql.Data.Entity (6.10.7)
It will also install the needed versions of the Nuget packages MySql.Data (6.10.7), EntityFramework (6.1.3), and BouncyCastle (1.8.3.1).
The MySql.Data.Entity package says it depends of Google.Protobuf, but it didn't install it and it works fine for me.
It added References in my project to BouncyCastle.Crypto (1.8.3.0), EntityFramework (6.0.0.0), MySQL.Data (6.10.7.0), and MySql.Data.Entity.EF6 (6.10.7.0).
Close Visual studio
Install 'MySQL for Visual Studio' (1.2.8)
Install 'Connector/NET' (6.10.7)
Delete the bin and obj folders
Open Visual Studio and Rebuild Solution
Add New Item > ADO.NET Entity Data Model > Now you're in the wizard
Select EF Designer from database
On the next screen ('Entity Data Model Wizard'), click New Connection...
On the 'Connection Properties' screen click the Change... button for the 'Data source'
You should be able to select the MySQL Database as the 'Data source'
The 'Data provider' should auto-populate with .NET Framework Data Provider for MySQL
Yay! Continue on like you normally would
For posterity, here's the app.config for my WPF application:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
<!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 --></configSections>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />
</startup>
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
<parameters>
<parameter value="v13.0" />
</parameters>
</defaultConnectionFactory>
<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
<provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.Entity.EF6, Version=6.10.7.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d" />
</providers>
</entityFramework>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="MySql.Data" publicKeyToken="c5687fc88969c44d" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-6.10.7.0" newVersion="6.10.7.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>
<connectionStrings>
<add name="MyDB" connectionString="metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;provider=MySql.Data.MySqlClient;provider connection string="server=my.example.com;user id=NotMyRealUserID;password=NotMyRealPassword;persistsecurityinfo=True;database=MyDatabase"" providerName="System.Data.EntityClient" />
</connectionStrings>
</configuration>
I'm not sure what created this, but I have a 'User variable' in my 'Environment Variables' named MYSQLCONNECTOR_ASSEMBLIESPATH with value C:\Program Files (x86)\MySQL\MySQL Connector Net 6.10.7\Assemblies\v4.5.2

At appsettings.json:
"ConnectionStrings": { "DefaultConnection": "Server=localhost;database=MusicStoreDB;user id=root;Charset=utf8;" },
At ConfigureServices() in Startup.cs :
using Microsoft.EntityFrameworkCore; using MySql.Data.MySqlClient; using Microsoft.Extensions.Configuration; using Microsoft.Extensions.DependencyInjection;
... services.AddDbContext(options => options.UseMySQL(Configuration.GetConnectionString("DefaultConnection")));
Note: Change to:
UseMysql <-------------- When using Pompelo EntityFrameworkCore

WPF/EF/SQLite The server was not found or was not accessible

I have been pulling my hair for many hours on this. I'm new to C# et .NET so I apologize if this is something trivial.
I'm trying to use WPF with Entity framework + SQLite.
I have managed to connect to the SQLite database by manually doing:
var connection = ConfigurationManager.ConnectionStrings["AccountHelper.Properties.Settings.AccountHelperConnectionString"].ConnectionString;
m_dbConnection = new SQLiteConnection(connection);
executeReader();
I get the following error:
A network-related or instance-specific error occurred while
establishing a connection to SQL Server. The server was not found or
was not accessible. Verify that the instance name is correct and that
SQL Server is configured to allow remote connections. (provider: SQL
Network Interfaces, error: 50 - Local Database Runtime error occurred.
The specified LocalDB instance does not exist.
I really have no clue on how to fix this. It is really frustrating!
EDIT: I answered this with a tutorial to configure everything properly.

So to answer my direct question above, the issue was that TextContext didn't know about the connection string. So if you give the same name to your Context as your string value, it will remove this error message.
That said, the configuration was completely wrong. I managed to make it working. Because I struggle a lot, I will share what I did to have it working.
Step to step guide to configure it
Configuration of a WPF project to work with Entity Framework (ADO.NET) and SQLite
Configuring this can be really tricky, even more if you have tried other methods before. So I advise to completely uninstall any SQLite software you might have installed.
1) Depending on your visual studio version, install sqlite-netFx45-setup-bundle-x86-2012-1.0.93.0.exe or equivalent. You can find it on sqlite.org. Few points:
I know for a fact that the 1.0.98.0 and 1.0.99.0 won't work with visual studio 2012. It works but you get an issue when creating your ADO.NET item in the project.
On this webpage, you can't find the old version, you will have to manually modify the URL to get the version you want.
On this webpage, make sure to select a version that has "This is the only setup package that is capable of installing the design-time components for Visual Studio 2013. " visual studio 2013 or not.
Install the exe and make sure to tick the designer related component during the install.
2) Create a new WPF project. Again, if you use a project you already modified, you might have some config issues. You better start a new project, do the config and once you know how to do it, port it to your project.
3) Install the Entity framework via the nugget manager.
4) Add manually (NOT WITH THE NUGGET MANAGER !!!) the following references that you can find in Assemblies -> Extension:
System.Data.SQLite Core
System.Data.SQLite Designer
System.Data.SQLite for Entity Framework
System.Data.SQLite for LINQ
5) Add a new item to this project -> Data -> ADO.NET blabla. Name it as you wish and create. You will need to create a connection for it. This is where if you don't have a compatible SQLite version, you won't be able to create a SQLite connection.
6) Then make sure your App.config look like the following, you might need to change the provider:
<configuration>
<configSections>
<!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
</startup>
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
<parameters>
<parameter value="mssqllocaldb" />
</parameters>
</defaultConnectionFactory>
<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
<provider invariantName="System.Data.SQLite" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6" />
</providers>
</entityFramework>
<system.data>
<DbProviderFactories>
<remove invariant="System.Data.SQLite" />
<add name="SQLite Data Provider" invariant="System.Data.SQLite" description="Data Provider for SQLite" type="System.Data.SQLite.SQLiteFactory, System.Data.SQLite" />
</DbProviderFactories>
</system.data>
<connectionStrings>
<add name="AccountHelperEntities" connectionString="metadata=res://*/AccountHelperModel.csdl|res://*/AccountHelperModel.ssdl|res://*/AccountHelperModel.msl;provider=System.Data.SQLite;provider connection string='data source="W:\visual studio projects\AccountHelper\AccountHelper\Data\AccountHelper.sqlite3"'" providerName="System.Data.EntityClient" />
</connectionStrings>
</configuration>
7) You are good to go.
You can see the project source code on this link. Check the code from the First commit, it contains everything you need. The other commits are project specific.

Connection String in Unit Test App.Config is ignored: SQLExpress gets set to LocalDB

I have a load of unit tests that were running fine in Visual Studio 2013. I dont know if it is related, but I can't think of what else might have changed. I have moved my project to VS2015.
Now whenever I run my unit tests, all the tests that use a data context fail with an error indicating they are trying to use (localdb)\V11.0 and integrated security to access the database.
However, my development database is on .\sqlexpress and has a SQL login.
I've been through every config file, including the app.config in the unit test project, and they all specify the correct database. If I debug step through the code I can reach the line where the data context is created and inspect its properties and see the connection string is wrong, but I can't see where it is coming from.
Here's the relevant bit of my test project's app.config file:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>
<connectionStrings>
<add name="speedEntitiesDev" connectionString="metadata=res://*/mydb.csdl|res://*/mydb.ssdl|res://*/mydb.msl;provider=System.Data.SqlClient;provider connection string="Server=.\sqlexpress;Database=thedatabase;User ID=theuser;Password=thepassword;Connection Timeout=30;MultipleActiveResultSets=True"" providerName="System.Data.EntityClient" />
</connectionStrings>
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework">
<parameters>
<parameter value="Server=.\sqlexpress;Database=thedatabase;User ID=theuser;Password=thepassword;Connection Timeout=30;MultipleActiveResultSets=True" />
</parameters>
</defaultConnectionFactory>
<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
</providers>
</entityFramework>
</configuration>
When I step into the unit test this is what the property inspector says is the value of the connection string is:
"Data Source=(localdb)\\v11.0;Initial Catalog=thedatabase;Integrated Security=True"
Note that the database name is correct, but everything else is wrong.
I did previously have a database hosted locally in localdb but after upgrading my development computer I stopped using it.
UPDATE:
I've discovered that if I rename the connection in the above file, then this breaks the test in a different way. Then I get an error that the connection string is not found:
System.InvalidOperationException: No connection string named 'speedEntitiesDev' could be found in the application config file..
Other changes to the connection string also have an effect (like if I change the database name, the connection goes to the new database name, and uses the login and password I supply.)
System.Data.Entity.Core.EntityException: The underlying provider failed on Open. ---> System.Data.SqlClient.SqlException: Cannot open database "thedatabase123" requested by the login. The login failed. Login failed for user 'theuser'..
When I set the connection string back to "thedatabase" it resets to using localdb and integrated security. It's like it's got an alias going or something.

After diving through the code for a few days, I noticed that in one older library referenced by every class tested by every failing test, there was a data update written as:
dc.SubmitChanges();
and it hit me, this class was using LINQ to Sql instead of Entity Framework. Somehow the class using LINQ to Sql was altering the connection string and defaulting to (localdb) which was what we were using when that library was written.
I changed the class to use Entity Framework instead and suddenly all my tests started respecting the connection string again.
This was weird because
The old referenced library didn't actually do any data updates any more (the data update code in it was legacy and long since placed elsewhere)
The old library didn't even have a valid reference to the data class that supplied its connection string
Despite this, just referencing the old library via the unit tests caused connection string weirdness.

Windows Service referencing Entity Framework 6 fails when deployed

I have a .Net 4.5.1 Console application configured as a Windows Service (derives from ServiceBase), using EntityFramework 6.1 installed via the Nuget package.
It works fine running locally (where I run it as a console application).
I deploy it to a Windows Server 2008 machine which has .Net 4.5.2 installed, register it as a Windows Service, and successfully start the service.
The service has a timer that does work every 90 seconds. The first time it does work (after 90 seconds), when it attempts to read from a SQL Server database, it fails with this error message:
System.Configuration.ConfigurationErrorsException: The 'DbProviderFactories' section can only appear once per config file.
I looked into the 2 machine.config files on the machine (in the .Net 2 and 4 folders) and verified that each has only a single DbProviderFactories section. There is no DbProviderFactories in my service app.config. The EventViewer does not have any information. I reinstalled .Net 4.5.2 and restarted the server to no avail.
How can I find out where is it trying to load two DbProviderFactories sections?
I'm adding this next bit of information just in case it is germane.
The second time the service does work (after 180 seconds), when it attempts to read from the same SQL Server database it fails with a different error message:
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.
This second error message is similar to this issue:
No Entity Framework provider found for the ADO.NET provider with invariant name 'System.Data.SqlClient'
but unfortunately I've already implemented all the suggestions to fix it.
I installed Entity Framework 6 from the Nuget package in both my data access layer AND my Console App windows service. The NuGet installer inserted the required sections into my app.config:
<configSections>
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
</configSections>
and
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
</providers>
</entityFramework>
I deployed what Visual Studio puts in my bin folder when I build. The deployment includes both EntityFramework.dll and EntityFramework.SqlServer.dll
My database connection string is:
<connectionString value="data source=SQLServerName;initial catalog=DatabaseName;integrated security=true;persist security info=True" />
The windows service runs under an identity that has access to the database.
This second error continues until I shut off the service.

Turned out this was the answer: The 'DbProviderFactories' section can only appear once per config file
When I stated "I looked into the 2 machine.config files on the machine (in the .Net 2 and 4 folders) and verified that each has only a single DbProviderFactories section." that was false. There was a duplicate, I simply did not see it the first time I looked.