c# – DbContext继承更新 – 数据库错误

public class AgileDbContextBase : DbContext
{
    public DbSet<Account> Accounts { get; set; }
    public DbSet<User> Users { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // base.OnModelCreating(modelBuilder);
        // TODO configure relations here!
        modelBuilder.Configurations.Add(new AccountEntityConfiguration())
            .Add(new UserEntityConfiguration());
    }
}

和

public class LoadContext : AgileDbContextBase
{
    #region Public Properties
    public DbSet<ProjectLoadEstimate> ProjectLoadEstimates { get; set; }
    public DbSet<OccupationType> OccupationTypes { get; set; }
    public DbSet<LoadReport> LoadReports { get; set; } 
    #endregion

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Configurations.Add(new ProjectLoadEstimateConfiguration())
            .Add(new OccupationTypeEntityConfiguration())
            .Add(new LoadReportEntityConfiguration());
    }
}

其中一个实体使用AgileDbContextBase上下文中的另一个实体,这里是：

public class LoadReport : BaseEntity
{
    /// <summary>
    ///     The date of load report has been created
    /// </summary>
    public virtual DateTime Created { get; set; }

    /// <summary>
    ///     The project manager
    /// </summary>
    public User ProjectManager { get; set; }

    /// <summary>
    ///     The Id of project manager
    /// </summary>
    public int ProjectManagerId { get; set; }
}

两个上下文都在使用自动迁移.
问题是,当我尝试在LoadContext上更新数据库时,PackageManager说

There is already an object named ‘Accounts’ in the database.

看起来它试图重新创建已经存在的表.怎么避免呢？
如何告诉代码优先来自LoadContext它必须在数据库中创建唯一的表,这些表被定义为DbSet<>在LoadContext中？
(也许是一些解决方法)？
附：两个上下文都使用相同的连接字符串.

感谢您的时间！