Prior to version 2.0 of EF Core, your options were limited to changing the command timeout for the DbContext, running the migration and then resetting the timeout value (or not):
public SampleContext() { Database.SetCommandTimeout((int)TimeSpan.FromMinutes(5).TotalSeconds); }
The IDesignTimeDbContextFactory was introduced in EF Core 2.0 to alleviate
this (and other) problems associated with configuring DbContext objects
differently for certain design-time tasks, such as migrations.
This interface is only intended for use with design time tools such as
migrations. The tools are configured to search the assembly containing the
DbContext (or the one designated as the startup assembly) for a type that
implements the interface. If one exists, it is instantiated and its CreateDbContext method is called which returns the derived
DbContext - enabling
you to configure the context in a different manner to the way it is configured
for runtime use. As such, it provides a hook for overriding the construction of
the DbContext type.
The following example illustrates the use of IDesignTimeDbContextFactory to
override the creation of SampleContext, specifying a command timeout value of 10
minutes, as opposed to the default 30 seconds, or whatever value has been
specified for the runtime version of the context:
public class SampleContextFactory : IDesignTimeDbContextFactory<SampleContext> { public SampleContext CreateDbContext(string[] args) { var optionsBuilder = new DbContextOptionsBuilder<SampleContext>(); optionsBuilder.UseSqlServer( @"Server=.\;Database=db;Trusted_Connection=True;", opts => opts.CommandTimeout((int)TimeSpan.FromMinutes(10).TotalSeconds) ); return new SampleContext(optionsBuilder.Options); } }
Finally, you must ensure that your context has a constructor that takes a
DbContextOptions object as a parameter:
public SampleContext(DbContextOptions options) : base(options) { }
It should be noted at this stage that the string[] args
parameter on the CreateDbContext method is not currently
implemented. Decisions have yet to be made on
how arguments can be passed to this method via the various design-time tools
that discover types that implement the interface.
