问Dbcontext无法迁移，因为架构不存在？

EN

public abstract class IntegrationTestsBase<T> : IDisposable
  where T : DbContext
{
  private readonly string _schema;
  private readonly string _historyTableName;
  private readonly DbContextOptions<T> _options;

  protected T DbContext { get; }

  protected IntegrationTestsBase()
  {
    _schema = Guid.NewGuid().ToString("N");
    _historyTableName = "__EFMigrationsHistory";

    _options = CreateOptions();
    DbContext = CreateContext();
    DbContext.Database.Migrate();
  }

  protected abstract T CreateContext(DbContextOptions<T> options, 
                                     IDbContextSchema schema);

  protected T CreateContext()
  {
    return CreateContext(_options, new DbContextSchema(_schema));
  }

  private DbContextOptions<T> CreateOptions()
  {
    return new DbContextOptionsBuilder<T>()
        .UseNpgsql($"Server=(local);Database=Demo;...", 
                builder => builder.MigrationsHistoryTable(_historyTableName, _schema))
        .ReplaceService<IMigrationsAssembly, DbSchemaAwareMigrationAssembly>()
        .ReplaceService<IModelCacheKeyFactory, DbSchemaAwareModelCacheKeyFactory>()
        .Options;
  }

  public void Dispose()
  {
    DbContext.GetService<IMigrator>().Migrate("0");
    DbContext.Database.ExecuteSqlCommand(
           (string)$"DROP TABLE [{_schema}].[{_historyTableName}]");
    DbContext.Database.ExecuteSqlCommand((string)$"DROP SCHEMA [{_schema}]");

    DbContext?.Dispose();
  }
}

public class SchemaContext : DbContext, IDbContextSchema
{
    public virtual DbSet<Schema>? SchemaModel { get; set; }

    public SchemaContext()
    {
    }

    public SchemaContext(DbContextOptions<SchemaContext> options, IDbContextSchema schema = null)
        : base(options)
    {
        Schema = schema.Schema;
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.HasDefaultSchema(Schema);
        //base.OnModelCreating(modelBuilder);
        modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());
    }

    public string Schema { get; }
}