我有以下代码。
为什么我的导航属性(课程中的要求和要求中的课程)为空?
public class Course : AbsEntity {
[Key]
public string Title { get; set; }
public string Term { get; set; }
public int Year { get; set; }
public string CourseId { get; set; }
public double GradePercent { get; set; }
public string GradeLetter { get; set; }
public string Status { get; set; }
public int ReqId { get; set; }
public Requirement Requirement { get; set; }
}
public class Requirement : AbsEntity {
[Key]
public int ReqId { get; set; }
public string ReqName { get; set; }
public ICollection<Course> Courses { get; set; }
}
// In DbContext
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Course>().HasOne(c => c.Requirement).WithMany(r => r.Courses).HasForeignKey(c => c.ReqId);
modelBuilder.Entity<Requirement>().HasMany(r => r.Courses).WithOne(c => c.Requirement);
}
首先,您不需要两次配置关系,只需执行一次:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Course>().HasOne(c => c.Requirement)
.WithMany(r => r.Courses)
.HasForeignKey(c => c.ReqId);
}
第二件事是,如果您正在执行查询并且希望延迟加载相关属性,恐怕这是不可能的。 EF 7 不支持延迟加载 https://github.com/aspnet/EntityFramework/issues/3312然而。正如你所看到的,有一个积压项目 https://github.com/aspnet/EntityFramework/issues/3797跟踪延迟加载。因此,如果您需要加载相关实体,您应该使用显式加载Include
method:
var query= ctx.Courses.Include(c=>c.Requirement).Where(...)...;
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