/// <summary>
/// 向给定的帖子上传图片。
/// </summary>
/// <param name="dataFacade"></param>
/// <param name="postId">帖子 ID。</param>
/// <param name="images">图片 ID 及对应图片的数据流工厂。</param>
/// <returns></returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="images"/>为null
/// </exception>
/// <exception cref="PostNotFoundException">
/// 指定的帖子不存在
/// 或
/// 帖子存在但其删除标记为true
/// </exception>
public static async Task UpdatePostImages(this IDataFacade dataFacade,
int postId, IReadOnlyDictionary <int, Func <Stream> > images)
{
if (images == null)
{
throw new ArgumentNullException(nameof(images));
}
// TODO: 在这里添加代码对 images 执行验证
var indexEntity = await dataFacade.Posts
// 下面的语句中务必使用 e.IsRemoved == true 以正确引导 EF Core 建立查询
.Where(e => e.Id == postId && e.IsRemoved == false)
.FirstOrDefaultAsync();
if (indexEntity == null)
{
// 指定的帖子不存在
throw new PostNotFoundException();
}
var contentId = new ObjectId(indexEntity.ContentId);
var contentEntity = await dataFacade.FindPostContentEntity(contentId);
// 删除已有的、被覆盖的图片数据
var removeTasks = new List <Task>();
foreach (var imageIndex in images.Keys.Where(i => i >= 0 && i < contentEntity.ImageIds.Length))
{
var imageId = contentEntity.ImageIds[imageIndex];
if (imageId == null)
{
continue;
}
removeTasks.Add(dataFacade.RemoveImage(imageId.Value));
}
await Task.WhenAll(removeTasks);
// 将图片上传至数据源
var imageIds = new ConcurrentDictionary <int, ObjectId?>();
var uploadTasks = new List <Task>();
foreach (var(index, imageDataStreamFactory) in images)
{
var imageDataStream = imageDataStreamFactory();
uploadTasks.Add(dataFacade.UploadImage(imageDataStream)
.ContinueWith((t, i) =>
{
imageDataStream.Close();
imageIds.TryAdd((int)i, t.Result);
}, index));
}
await Task.WhenAll(uploadTasks);
// 更新内容实体对象
await dataFacade.UpdatePostContentImageIds(contentId, imageIds);
// 更新索引实体对象中的上次更新时间戳
indexEntity.UpdateTime = DateTime.Now;
await dataFacade.CommitChanges();
}