如何使用 .NET Core EF 即时创建数据库

Question

I'm having an issue with dotnet ef . I'm trying to create a new database for every subdomain encountered. I've learned I can use the _context.Database.Migrate() here, but it seems it's only possible in the Startup & Program classes.

How can I do this when the program is running already? Since I can only get the subdomain when the app is running

Here's what I've tried:

// Db Context
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) 
{
     // _ecosystemServices.GetSubdomain gets the domain
     var subdomain = _ecosystemServices.GetSubDomain(_accessor);

     // _ecosystemServices.GetConnectionString returns the appropriate connection  string based on the subdomain
     optionsBuilder.UseSqlServer(_ecosystemServices.GetConnectionString(subdomain));         

     // Attempting to create the database
     _context.Database.Migrate();
}

But this doesn't work and I get a circular dependency error. What should I do?

Thanks in advance.

Answer 1

With EF Core you can use one of

context.Database.Migrate()

or

context.Database.EnsureCreated(),

where context is DbContext .

Where you call any of these depends on the logic of your app, but in OnConfiguring() is definitely not the right place since when database has to be created EF first creates the model and therefore calls OnConfiguring() . Hence you should get stack overflow message.

As of circular dependency I cannot tell but either the C# compiler is too smart and translates possible stack overflow to circular dependency (which I doubt, frankly), or the source of the error comes from somewhere else.

You should be aware however, of the differences between Migrate() and EnsureCreatd() . The second one does not apply the migrations in your code. Here's an answer by Rowan Miller to a similar question about both methods in Github :

You would either call EnsureCreated() or Migrate(). EnsureCreated() is an alternative that completely skips the migrations pipeline and just creates a database that matches you current model. It's good for unit testing or very early prototyping, when you are happy just to delete and re-create the database when the model changes.

You can just replace all your code with db.Database.Migrate();