EF代码首先不使用npgsql创建表

Question

我首先使用EF代码和Npgsql。一切都很好，直到我尝试使用contextclassObj保存更改

public class EmployeeRepository
{
    private ESAppraisalcontext DBAccessObj = null;
    public EmployeeRepository()
    {
        DBAccessObj = new ESAppraisalcontext();
        DBAccessObj.Employees.Add(new Employee { EmployeeCode = "1", EmployeeName = "shuk" });
        DBAccessObj.SaveChanges();            
    }
}  

在SaveChanges()点，它给出了一个异常，即Relation \ ESTables.Employee \不存在。这是我的上下文类：

public class ESAppraisalcontext : DbContext
{
    public DbSet<Entity> Entities { get; set; }
    public DbSet<Employee> Employees { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.HasDefaultSchema("ESTables");
            base.OnModelCreating(modelBuilder);
    }
}

我的模特：

public class Employee 
{
    [Key]
    public string EmployeeCode { get; set; }
    public string EmployeeName { get; set; }
    public string EmailId { get; set; }
    public string DomainName { get; set; }
    public int DesignationId { get; set; }
    public int DepartmentId { get; set; }
    public string MgrCode { get; set; }
    public int LocationId { get; set; }
    public DateTime DOJ { get; set; }
    public bool IsActive { get; set; }
    public bool IsEligibleForCycle { get; set; }
    public bool IsNonEligibleApprover { get; set; }

    [ForeignKey("DepartmentId")]
    public Departments department { get; set; }
    [ForeignKey("DesignationId")]
    public Designations designation { get; set; }
    [ForeignKey("LocationId")]
    public Locations Loation { get; set; }
}