How can I load the connection string from App.config or WebConfig.config in Entity Framework Core

Question

In the old versions I can give the connection string directly in the DbContext constructor.

Example in EF v6: My connection string in the App.config is given below:

  <connectionStrings>
    <add name="DatabaseConnecionString"
    connectionString="Data Source=.;Initial Catalog=db;Integrated Security=true"
    providerName="System.Data.SqlClient"/>
  </connectionStrings> 

---

var myDbContext = MyDbContext("name=DatabaseConnecionString");

When I do the same thing with EF 7 / Core I get an error?

Answer 1

In Entity Framework 7/Core, you cannot pass the connection string name to the DbContext base constructor like in the past but there is another solution for the problem.

Solution I:

var optionsBuilder = new Microsoft.EntityFrameworkCore.DbContextOptionsBuilder();
var connectionString = ConfigurationManager.ConnectionStrings["DatabaseConnecionString"].ConnectionString;
optionsBuilder.UseSqlServer(connectionString);
 using (var dbContext = new DatabaseContext(optionsBuilder.Options))
 {
    dbContext.Users.Add(new User() { Name = "Bassam" });
    dbContext.SaveChanges();
 }

Solution II:

If you want to use the provided connection string for the database migrations, then you have to put the loading in the DbContext.

public class DatabaseContext : DbContext
{
    public DbSet<User> Users { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
      var connectionString = ConfigurationManager.ConnectionStrings["DatabaseConnecionString"].ConnectionString;
      optionsBuilder.UseSqlServer(connectionString);
    }

    public DatabaseContext()
    {
    }

    public DatabaseContext(DbContextOptions s)
    : base(s)
    {
    }
}

If the App.config is not in your Assembly(dll/exe) then you have to give the the startup project with the data migration command Add-Migration/Update-Migration.