我有一个未与我的实体连接的实体dbcontext。我想改变那个。但是，已经存在与相同的实体的另一个实例dbcontext。如果仅添加新实体，则会收到错误消息，即已附加具有相同主键的实体。
我尝试了多种方法来dbcontext成功删除旧实体。如何用新实例替换旧实例？
注意：我不想复制值，而是要将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);
为了澄清：我已经覆盖Equals了检查Id而不是参考。
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);
}
我对此进行了调查，并希望与我分享一下结果。我使用反射作为获取实体属性名称的捷径。但是有可能像@Florian Haider所说的那样不加思考地得到它。您可以使用answer和this。
// 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);
}
}
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