分离实体EF不支持延迟加载

Question

我需要帮助我的新项目进行学习。我正在使用linq和EF，并从数据库获取数据。但显示我的代码在以下错误]

该班级有很多科目：第1级有这些科目清单英语，科学，数学错误：

InvalidOperationException：生成警告错误'Microsoft.EntityFrameworkCore.Infrastructure.DetachedLazyLoadingWarning'：试图延迟加载导航属性“ ClassSubject”“ SubjectProxy”类型的独立实体。不支持延迟加载用于分离的实体或已加载的实体'AsNoTracking（）'。可以抑制或记录此异常将事件ID'CoreEventId.DetachedLazyLoadingWarning'传递给'DbContext.OnConfiguring'中的'ConfigureWarnings'方法或'AddDbContext'。pri

vate readonly IGenericRepository<Subject> _subject;
        private readonly IGenericRepository<ClassSubject> _classSubject;
        public SubjectService(IGenericRepository<Subject> subject, IGenericRepository<ClassSubject> classSubject)
        {
            _subject = subject;
            _classSubject = classSubject;

        }
   public async Task<IEnumerable<ClassSubjectLib>> GetClassSubject()
    {
        var _dbs = await _classSubject.AllAsync().ConfigureAwait(false);
        return _dbs.Select(x => new ClassSubjectLib
        {
            ClassDetailsId = Convert.ToString(x.ClassDetailsId),
            SubjectId = Convert.ToString(x.SubjectId),
            SubjectInfo = _subject.FindBy(s => s.SubjectId == x.SubjectId)



        });
    }
    public class ClassSubjectLib
    {    
        public int ClassSubjectId { get; set; }
        public string ClassDetailsId{ get; set; }
        public string SubjectId { get; set; }  
        public IEnumerable<Subject> SubjectInfo { get; set; }
    }




 public  class Subject
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int SubjectId { get; set; }
        [Column(TypeName = "VARCHAR(100)")]
        public string SubjectName { get; set; }     
        public bool IsShow { get; set; }      

        public DateTime Created { get; set; }      
        public DateTime Updated { get; set; }      
        public virtual ICollection<ClassSubject> ClassSubject { get; set; }
    }



public class ClassSubject
    {       
        [Key]
        public int ClassSubjectId { get; set; }     
        public int ClassDetailsId { get; set; }      
        public int SubjectId { get; set; }

        public DateTime Created { get; set; }
        public DateTime Updated { get; set; }
        public virtual Subject Subject { get; set; }
        public virtual ClassDetails ClassDetails { get; set; }

    }

我需要类似数据

{
    "ClassSubjectId": 1,
    "ClassDetailsId": 1,
    "SubjectInfo": [{
        "SubjectName": "Abc",
        "SubjectId": 1
    }, {
        "SubjectName": "cfd",
        "SubjectId": 2
    }]
}

Data of database

Answer 1

摆脱无用的额外存储库层，然后做类似的事情：

public async Task<IEnumerable<ClassSubjectLib>> GetClassSubject()
{
    return dbContext.Set<ClassSubject>()
                    .Select(x => new ClassSubjectLib
                         {
                            ClassDetailsId = Convert.ToString(x.ClassDetailsId),
                            SubjectId = Convert.ToString(x.SubjectId),
                            SubjectInfo = x.Subjects.ToList()

                         })
                    .ToListAsync();
}

Answer 2

如错误消息所述，一旦您使用AsNoTracking()，由于无法再加载导航属性，因此延迟加载不起作用。