将上下文中的实体替换为同一实体的不同实例

Question

我有一个与我无关的实体dbcontext.我想改变这一点.但是,已经有另一个相同实体的实例附加到dbcontext.如果我只是添加我的新实体,我会收到一个错误,即已经附加了具有相同主键的实体.
我尝试了多种不同的删除旧实体的变体,dbcontext没有任何成功.如何用新的实例替换旧实例？
注意:我不想复制值,我想将我的新实体的这个实例附加到dbcontext.

var entity = new MyEntity { Id = 1 };
var logicalDuplicate = dbcontext.Set<MyEntity >().Local
    .FirstOrDefault(e => e.Equals(entity ));
if (logicalDuplicate != null)
{
    // remove logicalDuplicate from dbcontext
}
dbcontext.MyEntity.Attach(entity);

澄清:我已经覆盖Equals检查Id而不是参考.

Answer 1

试试这个:

if (logicalDuplicate != null)
{
    dbcontext.Entry(logicalDuplicate).State = EntityState.Detached;
    dbcontext.MyEntity.Attach(entity);
    dbcontext.Entry(entity).State = EntityState.Modified;
}
else
{
    dbcontext.MyEntity.Add(entity);
}

如何获得相关条目

我对此进行了调查,并希望与我的结果分享.我使用反射作为获取实体属性名称的简短方法.但是,正如@Florian Haider所提到的,它可以在没有反思的情况下得到它.你可以使用 答案和这个.

// Found loaded related entries that can be detached later.
private HashSet<DbEntityEntry> relatedEntries;

private DbContext context;

private List<string> GetPropertiesNames(object classObject)
{
    // TODO Use cache for that.
    // From question https://stackoverflow.com/questions/5851274/how-to-get-all-names-of-properties-in-an-entity
    var properties = classObject.GetType().GetProperties(BindingFlags.DeclaredOnly |
                                                              BindingFlags.Public |
                                                              BindingFlags.Instance);
    return properties.Select(t => t.Name).ToList();
}

private void GetRelatedEntriesStart(DbEntityEntry startEntry)
{
    relatedEntries = new HashSet<DbEntityEntry>();

    // To not process start entry twice.
    relatedEntries.Add(startEntry);
    GetRelatedEntries(startEntry);
}

private void GetRelatedEntries(DbEntityEntry entry)
{
    IEnumerable<string> propertyNames = GetPropertiesNames(entry.Entity);
    foreach (string propertyName in propertyNames)
    {
        DbMemberEntry dbMemberEntry = entry.Member(propertyName);
        DbReferenceEntry dbReferenceEntry = dbMemberEntry as DbReferenceEntry;
        if (dbReferenceEntry != null)
        {
            if (!dbReferenceEntry.IsLoaded)
            {
                continue;
            }

            DbEntityEntry refEntry = context.Entry(dbReferenceEntry.CurrentValue);
            CheckReferenceEntry(refEntry);
        }
        else
        {
            DbCollectionEntry dbCollectionEntry = dbMemberEntry as DbCollectionEntry;
            if (dbCollectionEntry != null && dbCollectionEntry.IsLoaded)
            {
                foreach (object entity in (ICollection)dbCollectionEntry.CurrentValue)
                {
                    DbEntityEntry refEntry = context.Entry(entity);
                    CheckReferenceEntry(refEntry);
                }
            }
        }
    }
}

private void CheckReferenceEntry(DbEntityEntry refEntry)
{
    // Add refEntry.State check here for your need.
    if (!relatedEntries.Contains(refEntry))
    {
        relatedEntries.Add(refEntry);
        GetRelatedEntries(refEntry);
    }
}