在类库中执行asp.net核心EF迁移而无需对连接字符串进行硬编码

Question

I would like to execute migration in separate environments. I'm working with Entity Framework and ASP.NET Core. For now I have this :

public class TemporaryDbContextFactory : IDbContextFactory<ApplicationDbContext>
{
    public ApplicationDbContext Create(DbContextFactoryOptions options)
    {
        var builder = new DbContextOptionsBuilder<ApplicationDbContext>();
        builder.UseSqlServer("Data Source=.\\LOCALHOST;Initial Catalog=MyDB;Integrated Security=True;MultipleActiveResultSets=true");

        return new ApplicationDbContext(builder.Options);
    }
}

This code is in a DAL class library who separate the database interactions from the server code.

It's ok to use this when executing migrations but I don't really like doing it like this.

The problem here is that I use a local database for development but we also have a development server and a staging server with different connection strings. What I can't manage to do is to find a way to not hardcode the connection strings in that class.

Is there a way to configure the connection strings for different environments and indicate which to use when executing the migrations ?

Answer 1

Yes, you can use environment variables for this.

Thats why you have appsettings.<EnvironmentName>.json

Configuration in ASP.NET Core
Not bad Microsoft article abount Working with multiple environments

FYI
Environment.GetEnvironmentVariable

Answer 2

You need to inject DbContextOptionsBuilder<ApplicationDbContext> into your factory constructor and then configure the DbContext in the main application's Startup.cs

public class TemporaryDbContextFactory : IDbContextFactory<ApplicationDbContext>
{
    private readonly DbContextOptionsBuilder<ApplicationDbContext> optionsBuilder;

    public TemporaryDbContextFactory(DbContextOptionsBuilder<ApplicationDbContext> optionsBuilder)
    {
        if(optionsBuilder==null)
            throw new ArgumentNullException(nameof(optionsBuilder));

        this.optionsBuilder = optionsBuiler;
    }

    public ApplicationDbContext Create(DbContextFactoryOptions options)
    {
        return new ApplicationDbContext(optionsBuilder.Options);
    }
}

And in Startup.cs:

services.AddDbContext<ApplicationDbContext>(options => {
    options.UseSqlServer(Configuration.GetConnectionString("MyConnectionString"));
});

Configuration.GetConnectionString("MyConnectionString") is shorthand for Configuration["ConnectionStrings:MyConnectionString"] .