An entity object cannot be referenced by multiple instances of IEntityChangeTracker 的解决方案
使用EF对建立了关系的表新增记录时出现:
An entity object cannot be referenced by multiple instances of IEntityChangeTracker 或一个实体对象不能由多个 IEntityChangeTracker 实例引用
在学习MVC+EF做demo时碰到的一个异常信息。在网上查了些,看得不是很明白,就自己折腾了一会儿。
先上出错的代码:
public class CollegeInfo { private StudentManageContext stuCtx=new StudentManageContext(); public Models.CollegeInfoModel GetModel(Guid collegeId) { var model = stuCtx.CollegeInfoes.SingleOrDefault(s => s.CollegeId == collegeId); return model; } public int Add(Models.CollegeInfoModel model) { stuCtx.CollegeInfoes.Add(model); int count = stuCtx.SaveChanges(); return count; } public int Update(Models.CollegeInfoModel model) { Models.CollegeInfoModel oldModel = stuCtx.CollegeInfoes.Find(model.CollegeId); oldModel = model; stuCtx.Entry(oldModel).State = System.Data.EntityState.Modified; return stuCtx.SaveChanges(); } }
public class DepartmentInfo { private StudentManageContext stuCtx=new StudentManageContext(); public Models.DepartmentInfoModel GetModel(Guid departmentId) { var model = stuCtx.DepartmentInfoes.SingleOrDefault(s => s.DepartmentId == departmentId); return model; } public int Add(Models.DepartmentInfoModel model) { stuCtx.DepartmentInfoes.Add(model); int count = stuCtx.SaveChanges(); return count; } public int Update(Models.DepartmentInfoModel model) { Models.DepartmentInfoModel oldModel = stuCtx.DepartmentInfoes.Find(model.DepartmentId); oldModel = model; stuCtx.Entry(oldModel).State = System.Data.EntityState.Modified; return stuCtx.SaveChanges(); } }
使用表关系图:
两个表是一对多的关系。DepartmentInfo 中的collegeInfoId是外键。
添加DepartmentInfo代码:
static void Main(string[] args) { Database.SetInitializer<StudentManageContext>(new DropCreateDatabaseIfModelChanges<StudentManageContext>());
CollegeInfoModel collegex = new BLL.CollegeInfo().GetModel(new Guid("B956CA6F-DD7D-4436-9099-484366A5F0B7"));
DepartmentInfoModel depart = new DepartmentInfoModel() { DepartmentId = Guid.NewGuid(), DepartmentName = "depart" + DateTime.Now.ToString(), CollegeInfoObj = collegex }; new BLL.DepartmentInfo().Add(depart); }
这时会出现An entity object cannot be referenced by multiple instances of IEntityChangeTracker 或一个实体对象不能由多个 IEntityChangeTracker 实例引用的异常
原因是 CollegeInfoModel collegex = new BLL.CollegeInfo().GetModel(new Guid("B956CA6F-DD7D-4436-9099-484366A5F0B7")); 和 new BLL.DepartmentInfo().Add(depart); 这两句代码使用的是两个不同的StudentManageContext 对象造成的,可以仔细看看出错代码,两个类都有 private StudentManageContext stuCtx=new StudentManageContext(); ,到这儿你是否明白了呢。简单的来说,你要做的操作都必须在同一DbContext上完成。注:StudentManageContext派生于DbContext.
解决方案一:
static void Main(string[] args) { Database.SetInitializer<StudentManageContext>(new DropCreateDatabaseIfModelChanges<StudentManageContext>()); CollegeInfoModel collegex = new BLL.CollegeInfo().GetModel(new Guid("B956CA6F-DD7D-4436-9099-484366A5F0B7")); DepartmentInfoModel depart = new DepartmentInfoModel() { DepartmentId = Guid.NewGuid(), DepartmentName = "depart" + DateTime.Now.ToString(), }; //new BLL.DepartmentInfo().Add(depart); 将这句代码改成下面两句 collegex.Departments.Add(depart); new BLL.CollegeInfo().Update(collegex); }
原因就是:Update时与GetModel用得时同一个DBContext。
解决方案二:
public class CollegeInfo:BaseModel { public Models.CollegeInfoModel GetModel(Guid collegeId) { var model = stuCtx.CollegeInfoes.SingleOrDefault(s => s.CollegeId == collegeId); return model; } public int Add(Models.CollegeInfoModel model) { stuCtx.CollegeInfoes.Add(model); int count = stuCtx.SaveChanges(); return count; } public int Update(Models.CollegeInfoModel model) { Models.CollegeInfoModel oldModel = stuCtx.CollegeInfoes.Find(model.CollegeId); oldModel = model; stuCtx.Entry(oldModel).State = System.Data.EntityState.Modified; return stuCtx.SaveChanges(); } } public class DepartmentInfo:BaseModel { public Models.DepartmentInfoModel GetModel(Guid departmentId) { var model = stuCtx.DepartmentInfoes.SingleOrDefault(s => s.DepartmentId == departmentId); return model; } public int Add(Models.DepartmentInfoModel model) { stuCtx.DepartmentInfoes.Add(model); int count = stuCtx.SaveChanges(); return count; } public int Update(Models.DepartmentInfoModel model) { Models.DepartmentInfoModel oldModel = stuCtx.DepartmentInfoes.Find(model.DepartmentId); oldModel = model; stuCtx.Entry(oldModel).State = System.Data.EntityState.Modified; return stuCtx.SaveChanges(); } } public abstract class BaseModel { protected StudentManageContext stuCtx = null; public BaseModel() { stuCtx = DataCache.GetCache("StudentManageContext") as StudentManageContext; if (stuCtx == null) { stuCtx = new StudentManageContext(); DataCache.SetCache("StudentManageContext", stuCtx); } } }
这样的话可以让CollegeInfo和DepartmentInfo共用同一个DBContext。