实体框架5 - 为什么在PropertyValue设置回原始状态后实体状态为"已修改"

Question

我使用EF5,并且在我将此实体的唯一更改的PropertyValue设置回原始值之后,不知道为什么实体具有"已修改"状态.

using (TestDbContext context = new TestDbContext())
        {
            string name = context.Person.First().Name;

            // count is 0
            int count = context.ChangeTracker.Entries().Count(e => e.State == EntityState.Modified);

            // Change Value
            context.Person.First().Name = "Test";

            // count is 1 
            count = context.ChangeTracker.Entries().Count(e => e.State == EntityState.Modified);

            // Revert Value
            context.Person.First().Name = name;


            context.ChangeTracker.DetectChanges();

            // count is 1 
            count = context.ChangeTracker.Entries().Count(e => e.State == EntityState.Modified);
        }

为什么？:(

Answer 1

因为实体框架仅跟踪数据是否被修改,而不是跟它的原始内容不同.

当实体不变时,我们使用一个漂亮的方法将状态重置为未修改:

    public static void CheckIfModified(EntityObject entity, ObjectContext context)
    {
        if (entity.EntityState == EntityState.Modified)
        {
            ObjectStateEntry state = context.ObjectStateManager.GetObjectStateEntry(entity);
            DbDataRecord orig = state.OriginalValues;
            CurrentValueRecord curr = state.CurrentValues;

            bool changed = false;
            for (int i = 0; i < orig.FieldCount && !changed; ++i)
            {
                object origValue = orig.GetValue(i);
                object curValue = curr.GetValue(i);
                if (!origValue.Equals(curValue) && (!(origValue is byte[]) || !((byte[])origValue).SequenceEqual((byte[])curValue)))
                {
                    changed = true;
                }
            }

            if (!changed)
            {
                state.ChangeState(EntityState.Unchanged);
            }
        }
    }

请注意,此方法适用于EF 4.0,而不适用于具有DbContext的较新版本.但是重写它以使用EF 4.1+没有问题,我已经自己做了,但我现在找不到代码.

Answer 2

谢谢提示:)

这是我的 EF5 (DbContext) 解决方案。我为从 ChangeTracker.Entries() 获得的每个 DbEnityEntry 调用此方法

    private void CheckIfDifferent(DbEntityEntry entry)
    {
        if (entry.State != EntityState.Modified) 
            return;

        if (entry.OriginalValues.PropertyNames.Any(propertyName => !entry.OriginalValues[propertyName].Equals(entry.CurrentValues[propertyName])))
            return;

       (this.dbContext as IObjectContextAdapter).ObjectContext.ObjectStateManager.GetObjectStateEntry(entry.Entity).ChangeState(EntityState.Unchanged);
    }