How can I implement DbContext Connection String in .NET Core?

.net c# entity-framework


My situation is quite similar to this link or at least my code is similar and I am trying to find a way to apply this same method in .NET Core syntax.

Pass connection string to code-first DbContext

My specific code is as follows:

public partial class CompanyFormsContext : DbContext
    public CompanyFormsContext()
        : base("name=CompanyFormsContext")

    public CompanyFormsContext(string connName)
        : base("name=" + connName)

I get an error saying:

Error CS1503 Argument 1: cannot convert from 'string' to 'Microsoft.EntityFrameworkCore.DbContextOptions' CompanyForms..NETCoreApp,Version=v1.0

when I go over the parenthesis in base("name=CompanyFormsContext") or base("name=" = connName).

What is the correct way of implementing this functionality in .NET Core?


I wanted to share that I have the following information for database connection in my appsettings.json file: (However, I do not have settings in the startup.cs)

  "Data": {
    "CompanyFormsContext": {
      "ConnectionString": "Server=(localdb)\\projectsv13;Database=companyforms;Trusted_Connection=True;"
    "CompanyFormsContextQA": {
      "ConnectionString": "Server=(localdb)\\projectsv13;Database=companyforms;Trusted_Connection=True;"

and I have found the following link Adding DbContextOptions in Startup.cs not registering data store in the website and I am wondering if a simple protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) will be enough to fix my connection or not?

From the link:

        options =>

Do I need this kind of a service in my Startup.cs?

5/23/2017 12:10:39 PM

Accepted Answer

Another option would be to call the base constructor that takes a DbContextOptions:

public BooksContext(string connectionString) : base(GetOptions(connectionString))

private static DbContextOptions GetOptions(string connectionString)
    return SqlServerDbContextOptionsExtensions.UseSqlServer(new DbContextOptionsBuilder(), connectionString).Options;
11/28/2018 6:14:24 AM

Popular Answer

Generally you are going to want to read it from config at start-up, and then use the connection string to configure an Entity Framework DbContext service for your process.

1) Add a line to your appsettings.json:

"DbConnectionString": "Server=s;Database=db;Trusted_Connection=True;",

2) Read the line in you Startup.cs class (after the Startup method is called to build the Configuration - so usually in the ConfigureServices method) like this:

var connection = Configuration["DbConnectionString"];

3) If using Entity Framework add a database context service (MyDbContext is the context class generated by EF). You also want to tell the built-in dependency injection how to instantiate your database context:

services.AddDbContext<MyDbContext>(options => options.UseSqlServer(connection));
services.AddScoped<IMyDbContext, MyDbContext>();

Where IMyDbContext is (at it's simplist) just an interface you've extracted from your MyDbContext

4) Now you can define your controller to take a MyDbContext and the DI will take care of building it and passing it in when the controller is invoked:

public MyController(IMyDbContext context)
    _context = context  // store for later use

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