//实体类
  [Table("invoiceinfo", Schema = "obs")]
    public class invoice
    {
      
        [Key]
        public string invoice_num { get; set; }

        public string merchant_id { get; set; }

        public DateTimeOffset? verify_time { get; set; }

        //one to many
       public virtual IList<invoice_relation> invoice_file_list { get; set; }

     　　//one to one
        public virtual business invoice_business { get; set; }

      
    }

//数据库  PostgreDbContext相关配置

protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);
            builder.Entity<invoice>().HasMany(i => i.invoice_file_list).WithOne().HasForeignKey(f => f.invoice_num);
            builder.Entity<invoice>().HasOne(i => i.invoice_business).WithMany().HasForeignKey(i => i.merchant_id);
        }

 //.file为invoice_file_list类中字段属性，.invoiced_party为invoice_business字段属性
 IQueryable<invoice> invoiceList = _postgreDbContext.invoice.AsNoTracking().Include("invoice_file_list.file").Include("invoice_business.invoiced_party");