Entity Framework 2.1 映射的问题

Question

我将一个插件从 .NET Framework 4.6.1 升级到 .NET Core 2.1，但遇到 EF 映射问题。

我有 4.6.1 中的类扩展基本图片类：

public partial class PictureExt : Picture
{
    public virtual string ExternalUrl { get; set; }
}

基类：

public partial class Picture : BaseEntity
{
    public string MimeType { get; set; }
    public string SeoFilename { get; set; }
    public string AltAttribute { get; set; }
    public string TitleAttribute { get; set; }
    public bool IsNew { get; set; }
    public virtual PictureBinary PictureBinary { get; set; }
}

在 4.6.1 中我完成了映射：

    public PictureMap()
    {
        this.ToTable("Picture");
        this.HasKey(p => p.Id);
        this.Property(p => p.PictureBinary).IsMaxLength();
        this.Property(p => p.MimeType).IsRequired().HasMaxLength(40);
        this.Property(p => p.SeoFilename).HasMaxLength(300);
        this.Property(p => p.ExternalUrl).IsOptional();
    }

一切都很好

但在 .NET Core EF 中我完成了映射：

    public override void Configure(EntityTypeBuilder<PictureExt> builder)
    {
        builder.ToTable("Picture");
        builder.HasKey(picture => picture.Id);
        builder.Property(picture => 
        picture.MimeType).HasMaxLength(40).IsRequired();
        builder.Property(picture => picture.SeoFilename).HasMaxLength(300);
        builder.Property(p => p.ExternalUrl);
        base.Configure(builder);
    }

我有一个例外：

A key cannot be configured on 'PictureExt' because it is a derived type. The key must be configured on the root type 'Picture'. If you did not intend for 'Picture' to be included in the model, ensure that it is not included in a DbSet property on your context, referenced in a configuration call to ModelBuilder, or referenced from a navigation property on a type that is included in the model

我明白我做错了什么，但我不知道如何做对。 也许是这样的？ https://stackify.com/new-in-net-core-2-1/#post-19576-_kaymrlea07yf

但是如何实现呢？

Answer 1

您可以做的是确保您的DbContext 上没有DbSet<Picture> 或DbSet<BaseEntity>。如果以下解决方案不适用于您的情况，请更新您的问题，以便我们相应地更新我们的答案。 :)

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;
using System;
using Xunit;

public class Tests
{
    [Fact]
    public void Can_add_PictureExt()
    {
        var options = new DbContextOptionsBuilder<Context>()
            .UseInMemoryDatabase(Guid.NewGuid().ToString())
            .Options;

        using (var ctx = new Context(options))
        {
            ctx.Add(new PictureExt());
            ctx.SaveChanges();
        }

        using (var ctx = new Context(options))
        {
            Assert.Single(ctx.PictureExt);
        }
    }
}
public class Context : DbContext
{
    public Context(DbContextOptions<Context> options) : base(options) { }

    public DbSet<PictureExt> PictureExt { get; set; }

    //uncommenting any of the following DbSet will throw exception

    //public DbSet<Picture> Picture { get; set; }

    //public DbSet<BaseEntity> BaseEntity { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfiguration(new PictureExtConfiguration());
    }
}
public class PictureExtConfiguration : IEntityTypeConfiguration<PictureExt>
{
    public void Configure(EntityTypeBuilder<PictureExt> builder)
    {
        builder.ToTable("Picture");
        builder.HasKey(picture => picture.Id);
        builder.Property(picture =>
        picture.MimeType).HasMaxLength(40).IsRequired();
        builder.Property(picture => picture.SeoFilename).HasMaxLength(300);
        builder.Property(p => p.ExternalUrl);

        //commented out to simplify example
        //base.Configure(builder);
    }
}
public partial class PictureExt : Picture
{
    public virtual string ExternalUrl { get; set; }
}
public partial class Picture : BaseEntity
{
    public string MimeType { get; set; }
    public string SeoFilename { get; set; }
    public string AltAttribute { get; set; }
    public string TitleAttribute { get; set; }
    public bool IsNew { get; set; }

    //commented out to simplify example
    //public virtual PictureBinary PictureBinary { get; set; }
}
public class BaseEntity
{
    public int Id { get; set; }
}

Answer 2

一行修复：

public override void Configure(EntityTypeBuilder<PictureExt> builder)
{
    builder.ToTable("Picture");
    
    // turn off deriving
    builder.HasBaseType((Type) null);

    builder.HasKey(picture => picture.Id);
    builder.Property(picture => 
    picture.MimeType).HasMaxLength(40).IsRequired();
    builder.Property(picture => picture.SeoFilename).HasMaxLength(300);
    builder.Property(p => p.ExternalUrl);
    base.Configure(builder);
}