实体框架DB-First - 我可以从基础模型继承以添加我的功能吗？

Question

I'm creating a simple application in C#. One of it's features is adding invoices.

For this purpose I've created two tables in my database - Invoice and InvoiceLine, and used Entity Framework to map them for me. I needed to add some functionality for the InvoiceLine class, but I know you shouldn't edit the code created by Entity Framework. Instead, I decided to inherit from the class created by EF and add this functionality ontop of this class.

I did this, but now, when I'm trying to save it to the database, I get an error - 'System.InvalidOperationException: 'Mapping and metadata information could not be found for EntityType 'InvoiceRegister.Models.InvoiceLineModel'.

My question is - how can it be fixed? Also, is there a better way to achieve what I wanted? I wanted to do my project in MVVM, so I wanted to create a Model, and not do the functionality in my ViewModel.

Code:

Original class (InvoiceLine):

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated from a template.
//
//     Manual changes to this file may cause unexpected behavior in your application.
//     Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace InvoiceRegister.Models
{
    using System;
    using System.Collections.Generic;

    public partial class InvoiceLine
    {
        public int DocEntry { get; set; }
        public int LineId { get; set; }
        public int LineNum { get; set; }
        public string ItemName { get; set; }
        public double Amount { get; set; }
        public int TaxPrc { get; set; }
        public decimal NetAmnt { get; set; }
        public decimal TaxAmnt { get; set; }
        public decimal TotalAmnt { get; set; }
        public decimal Price { get; set; }

        public virtual Invoice Invoice { get; set; }
    }
}

My class. I want it to inherit from InvoiceLine:

namespace InvoiceRegister.Models
{
    public class InvoiceLineModel : InvoiceLine, INotifyPropertyChanged
    {
        private double _amount;

        public new double Amount
        {
            get { return _amount; }
            set
            {
                _amount = value;
                OnPropertyChanged("Amount");
                OnPropertyChanged("NetAmnt");
                OnPropertyChanged("TaxAmnt");
                OnPropertyChanged("TotalAmnt");
            }
        }

        private decimal _price;

        public new decimal Price
        {
            get { return _price; }
            set
            {
                _price = value;
                OnPropertyChanged("Price");
                OnPropertyChanged("NetAmnt");
                OnPropertyChanged("TaxAmnt");
                OnPropertyChanged("TotalAmnt");
            }
        }

        private int _taxPrc;

        public new int TaxPrc
        {
            get { return _taxPrc; }
            set
            {
                _taxPrc = value;
                OnPropertyChanged("TaxPrc");
                OnPropertyChanged("TaxAmnt");
                OnPropertyChanged("TotalAmnt");
            }
        }


        public new decimal TaxAmnt
        {
            get
            {
                return NetAmnt* TaxPrc/100;
            }
        }


        public new decimal NetAmnt
        {
            get
            {
                return  (decimal)Amount * Price;
            }
        }

        public new decimal TotalAmnt
        {
            get {return NetAmnt + TaxAmnt; }
        }

        public InvoiceLineModel()
        {
            this.LineNum = InvoiceViewModel.getNextLineNum();
        }
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string name)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }
}

Answer 1

You can do that in code first approach but not in the database first, so, basically, you need to update the database first. You are using a database first approach so you need the following steps:

1) Add new fields in the table in your case ("InvoiceLine") in the database directly

2) Once you add you can update EF Generated Model by right-clicking and updating model

3) While updating you need to select the table checkbox. (Image attach for your ref)

4) Once you update the EF model you can have properties available in EF generated class

Helping Resource: https://entityframework.net/ef-database-first

All done.