无法更新数据库中的现有条目

Question

当具有 Id 的条目已经存在时，我正在尝试使用 Entity Framework Core（带有 ASP .NET Core 的 C#）来更新数据库 (PostgreSQL) 中的条目，但这不起作用：

     public async Task SaveFileInfos(FileInfo fileInfo)
     {
        var foundFileInfo = _context.FileInfos.Where(f => f.FileId ==fileInfo.FileId).FirstOrDefault();

        if (foundFileInfo == null)
        {
            await _context.FileInfos.AddAsync(fileInfo);
        }
        else
        {
            _context.FileInfos.Update(fileInfo);
        }

        await _context.SaveChangesAsync();
    }

顺便说一下，ID 不能是 GUID，因为它必须是 34 位数字。

public class FileInfo : IFileInfo
{
    [Key]
    public string FileId { get; set; }
    public string FileName { get; set; }
}

如果我想更改已包含的条目，则会出现以下异常：

System.InvalidOperationException: The instance of entity type 'FileInfo' cannot be tracked because another instance with the same key value for {'FileId'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.ThrowIdentityConflict(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry, Boolean updateDuplicate)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NullableKeyIdentityMap`1.Add(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTracking(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges, Boolean modifyProperties)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState entityState, Boolean acceptChanges, Boolean modifyProperties, Nullable`1 forceStateWhenUnknownKey)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.PaintAction(EntityEntryGraphNode`1 node)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.AttachGraph(InternalEntityEntry rootEntry, EntityState targetState, EntityState storeGeneratedWithKeySetTargetState, Boolean forceStateWhenUnknownKey)
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.SetEntityState(InternalEntityEntry entry, EntityState entityState)
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.Update(TEntity entity)

我做错了什么？这一定是初学者的错误；-)

Answer 1

EF 更新被跟踪的实体。在这种情况下，foundFileInfo 是跟踪的实体，对于 EF，fileInfo 是一个新条目。

因此，如果您想更新条目，请尝试使用跟踪的实体。例如：

public async Task SaveFileInfos(FileInfo fileInfo)
 {
    var foundFileInfo = _context.FileInfos.FirstOrDefault(f => f.FileId == fileInfo.FileId);

    if (foundFileInfo == null)
    {
        await _context.FileInfos.AddAsync(fileInfo);
    }
    else
    {
        foundFileInfo.FileName = fileInfo.FileName;
    }

    await _context.SaveChangesAsync();
}