[英]EF 7: How to load related entities in a One-to-many relationship
我有以下代码。 为什么我的导航属性(课程要求和要求课程)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,您不需要两次配置您的关系,您只需要执行一次:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Course>().HasOne(c => c.Requirement)
.WithMany(r => r.Courses)
.HasForeignKey(c => c.ReqId);
}
第二件事是如果你正在进行查询并且你期望延迟加载相关属性,我恐怕是不可能的。 EF 7还不支持延迟加载 。 如您所见,有一个积压项目跟踪延迟加载。 因此,如果您需要加载相关实体,则应使用Include
方法使用显式加载:
var query= ctx.Courses.Include(c=>c.Requirement).Where(...)...;
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.