mysql - 在 EntityFrameworkCore 中加载相关数据时出错

Question

加载相关数据(类(class)的类(class)页面)时出现以下错误。

错误

MySqlException: Unknown column 'c.Coursepages.CoursepageId' in 'field list'

失败点:

var course = await _context.Courses.Include(c => c.Coursepages)
                .SingleOrDefaultAsync(m => m.Url == courseUrl);

应用程序数据库上下文:

        modelBuilder.Entity<Course>(entity =>
        {
            entity.ToTable("courses");

            entity.HasIndex(e => e.Id).HasName("idx_Courses_Id");

            entity.HasIndex(e => e.Url).HasName("uk_Url").IsUnique();

            entity.Property(e => e.Id).HasColumnType("int(11)");
        });

        modelBuilder.Entity<Coursepage>(entity =>
        {
            entity.ToTable("coursepages");

            entity.HasIndex(e => e.CourseId).HasName("idx_CoursePages_CourseId");

            entity.HasIndex(e => e.LessonId).HasName("idx_CoursePages_LessonId");

            entity.HasIndex(e => e.TopicId).HasName("idx_CoursePages_TopicId");

            entity.HasIndex(e => new { e.CourseId, e.LessonId, e.TopicId }).HasName("uk_CourseId_LessonId_TopicId").IsUnique();

            entity.Property(e => e.Id).HasColumnType("int(11)");
            entity.Property(e => e.CourseId).HasColumnType("int(11)");
            entity.Property(e => e.LessonId).HasColumnType("int(11)").HasDefaultValueSql("'0'");
            entity.Property(e => e.TopicId).HasColumnType("int(11)").HasDefaultValueSql("'0'");
            entity.HasOne(d => d.Course)
                .WithMany(p => p.Coursepages)
                .HasForeignKey(d => d.CourseId)
                .OnDelete(DeleteBehavior.ClientSetNull)
                .HasConstraintName("FK_CoursePages_Courses_CourseId");
        });

类(class)模型

public partial class Course
{
    public Course()
    {
        Coursepages = new List<Coursepage>();
    }

    public int Id { get; set; }
    public string Url { get; set; }

    public ICollection<Coursepage> Coursepages { get; set; }
}

类(class)页面模型:

public partial class Coursepage
{
    public int Id { get; set; }
    public int CourseId { get; set; }
    public int LessonId { get; set; }
    public int TopicId { get; set; }
    public Course Course { get; set; }
}

Note : I am using ASP.Net Core 2.0 with MySQL using Pomelo.EntityFrameworkCore.MySQL driver.

Answer 1

问题的原因是:

public List < Coursepage > Topics { get; set; }

EntityFramework 尝试将此属性映射到数据库，并假定主键为“CoursepageId”，但在数据库中找不到该主键。

Any property which is not directly mapped to Database should be labeled with NotMapped attribute.

所以类(class)页面模型必须是这样的:

public partial class Coursepage
{
    public int Id { get; set; }
    public int CourseId { get; set; }
    public int LessonId { get; set; }
    public int TopicId { get; set; }
    public Course Course { get; set; }

      //  If current page is a Lesson Page
      [NotMapped]
      public List<Coursepage> Topics { get; set; }
}

注意:导入命名空间System.ComponentModel.DataAnnotations.Schema以使用NotMapped属性。

引用文献:

• Including & Excluding Properties