Connection String Use .Net Core

Yes, you can absolutely use multiple connection strings in .NET Core, and you can use them together with ADO.NET and Entity Framework Core in the same application. This is very common in real projects.

Below is a clear, short, and practical explanation.

1. Define multiple connection strings (appsettings.json)

{
  "ConnectionStrings": {
    "EFConnection": "Server=.;Database=AppDb;Trusted_Connection=True;",
    "ADOConnection": "Server=.;Database=LegacyDb;Trusted_Connection=True;"
  }
}

You can add any number of connection strings.

2. Use connection string with Entity Framework Core

Program.cs / Startup.cs

builder.Services.AddDbContext(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("EFConnection")));

EF Core will use EFConnection only.

3. Use connection string with ADO.NET

string connStr = configuration.GetConnectionString("ADOConnection");

using SqlConnection con = new SqlConnection(connStr);
using SqlCommand cmd = new SqlCommand("SELECT * FROM Users", con);

con.Open();
using SqlDataReader reader = cmd.ExecuteReader();

ADO.NET will use ADOConnection.

4. Use BOTH EF Core and ADO.NET in the same service (Recommended)

public class UserService
{
    private readonly AppDbContext _context;
    private readonly IConfiguration _config;

    public UserService(AppDbContext context, IConfiguration config)
    {
        _context = context;
        _config = config;
    }

    public List GetUsersEF()
    {
        return _context.Users.ToList();
    }

    public DataTable GetUsersADO()
    {
        using SqlConnection con =
            new SqlConnection(_config.GetConnectionString("ADOConnection"));
        // ADO.NET logic
    }
}

This is fully supported
Clean and maintainable
Best for legacy + new code

5. Using multiple DbContexts (optional)

If you want multiple databases with EF Core:

builder.Services.AddDbContext(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DB1")));

builder.Services.AddDbContext(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DB2")));

When should you mix EF Core & ADO.NET?

Hi

Yes you can use Both connectionstrings as below-

{ "ConnectionStrings": { "DefaultConnection": "Server=.\\SQLEXPRESS;Database=Bar;Trusted_Connection=True;MultipleActiveResultSets=true", "NewConnection": "Server=.\\SQLEXPRESS;Database=Bar;Trusted_Connection=True;MultipleActiveResultSets=true" } }

Yes, you can use multiple connection strings in the same app. Check the implementation example below.
https://stackoverflow.com/questions/41525856/using-multiple-connection-strings

Yes you can

in appsettings.json file use the following syntax to define connection strings

{
  "ConnectionStrings": {
    "FirstConString": "connectionstring will go here"
    "SecondConString": "connectionstring will go here"
  },
}

yes you use for both like:

{ "ConnectionStrings":

{

"myconnectionstring1": "Server=1.1.1;Database=database1;Trusted_Connection=True;",

"myconnectionstring2": "Server=1.1.2;Database=database2;Trusted_Connection=True;" }

}

and Now we can read it in our code by calling the GetConnectionString method in the Microsoft.Extensions.Configuration namespace. like thiis type:

string connectionstring1= _configuration.GetConnectionString("myconnectionstring1");

string connectionstring2= _configuration.GetConnectionString("myconnectionstring2");

Yes you can make it..

Create one class for Ado connection initiation and another for your dbcontext... 

Yes, You can use both

To define the connection strings in appsettings.json it is important to specify it in the right section of the JSON structure.

{
  "ConnectionStrings": {
    "myDb1": "Server=myServer;Database=myDb1;Trusted_Connection=True;",
    "myDb2": "Server=myServer;Database=myDb2;Trusted_Connection=True;"
  }
}

Now we can read it in our code by calling the GetConnectionString method in the Microsoft.Extensions.Configuration namespace.

string myDb1ConnectionString = _configuration.GetConnectionString("myDb1");
string myDb2ConnectionString = _configuration.GetConnectionString("myDb2");

To be able to call the method you must import the Microsoft.Extensions.Configuration namespace like this:

using Microsoft.Extensions.Configuration;

Yes you can use both 

Hello Rajesh,

Please refer below link. 

https://code-maze.com/aspnetcore-multiple-databases-efcore/

Thanks

Naimish Makwana

Yes, you can use both, even i have used both in multiple projects.

Yes yo can use both togather,

https://social.msdn.microsoft.com/Forums/en-US/37176d9c-f27c-4c7a-954f-f78e6866ed9a/adonet-and-entitty-frame-work-together-in-a-project?forum=aspdotnetcore