如何使实体框架4内部缓存无效

Question

据我所知,Entity Framework实现了Identity Map Pattern,因此EF会在内存中缓存一些实体.

我举个例子吧.

var context = new StudentContext();

var student = context.Students.Where(st => st.Id == 34).FirstOrDefault();

// any way of changing student in DB
var anotherContext = new StudentContext();
var anotherStudent = anotherContext.Students.Where(st => st.Id == 34).FirstOrDefault();
anotherStudent.Name = "John Smith";
anotherContext.SaveChanges();

student = context.Students.Where(st => st.Id == 34).FirstOrDefault();
// student.Name contains old value   

有没有办法使第一个上下文的缓存无效并检索新student实体而无需重新创建上下文？

感谢帮助.

Answer 1

您必须强制EF重新加载实体.您可以为每个实体执行此操作:

context.Refresh(RefreshMode.StoreWins, student);

或者您可以进行查询:

ObjectQuery<Student> query = (ObjectQuery<Student>)context.Students.Where(st => st.Id == 34);
query.MergeOption = MergeOption.OverwriteChanges;
student = query.FirstOrDefault();

或者在对象集上全局更改它:

context.Students.MergeOption = MergeOption.OverwriteChanges;

Answer 2

尝试刷新上下文:

context.Refresh(RefreshMode.StoreWins, yourObjectOrCollection);

因此,在您的情况下,您需要访问ObjectContext

var objContext = ((IObjectContextAdapter)this).ObjectContext;

并刷新它:

objContext.Refresh(RefreshMode.StoreWins, anotherStudent);

更多信息:http://msdn.microsoft.com/en-us/library/bb896255.aspx