我一直在寻找,虽然它应该很简单,但我无法使其正常工作。根据我所看到的示例,到目前为止,这是我到达的地方:
SomeAppService.cs
public async Task<FileStream> Download(long? id)
{
var attachment = await _repository.FirstOrDefaultAsync(x => x.Id == id);
var fileStream = new FileStream($"{attachment.FileName}.{attachment.FileExtension}",
FileMode.Create, FileAccess.Write);
fileStream.Write(attachment.File, 0, attachment.File.Length);
return fileStream;
}
可以注意到,“ FileName”,“ FileExtension”和“ File”(即上述字节数组)存储在数据库中。附件可以是任何类型的文件,但Upload方法中的扩展名除外(未显示)。然后在我的控制器中有:
SomeController.cs
[AllowAnonymous]
[HttpGet("Download/{id}")]
public async Task<IActionResult> Download(long? id)
{
var fileStream = await appService.Download(id);
return new FileStreamResult(fileStream, "application/octet-stream");
}
但是,当我到达下载端点时,最终得到的文件名为“ response”,无扩展名,具有0个字节。
资源:
Return file in ASP.Net Core Web API
Return a FileResult from a byte[]
Save and load MemoryStream to/from a file(响应为255个upvotes使我有了将字节数组转换为文件流的想法,但我不知道这样是否可行)
谢谢大家,最后FileContentResult
做到了。
外观如下:
服务
public async Task<Attachment> Download(long? id)
{
return await _repository.FirstOrDefaultAsync(x => x.Id == id);
}
Controller
[AllowAnonymous]
[HttpGet("Download/{id}")]
public async Task<IActionResult> Download(long? id)
{
var attachment = await appService.Download(id);
return new FileContentResult(attachment.File,
MimeTypeMap.GetMimeType(attachment.FileExtension))
{
FileDownloadName = $"{attachment.NomeFile}.{attachment.FileExtension}"
};
}
[MimeTypeMap
可以找到here
如果要从实体框架的数据库Blob中流式传输文件而不将其加载到内存中。首先将数据模型分为两部分;
public class Attachment{
public int Id { get; set; }
public string Filename { get; set; }
public string ContentType { get; set; }
public virtual AttachmentBlob Blob { get; set; }
//...
}
public class AttachmentBlob{
public int Id { get; set; }
public byte[] File { get; set; }
}
将它们映射到相同的表,但不作为拥有的类型;
modelBuilder.Entity<Attachment>(e => {
e.HasOne(a => a.Blob)
.WithOne()
.HasForeignKey<AttachmentBlob>(b => b.Id);
});
modelBuilder.Entity<AttachmentBlob>(e => {
e.ToTable("Attachment");
});
然后您可以按字节数组或流的形式对其进行读写;
public static async Task Read(DbContext db, Attachment attachment, Func<Stream,Task> callback)
{
await db.Database.OpenConnectionAsync();
try {
var conn = db.Database.GetDbConnection();
var cmd = conn.CreateCommand();
var parm = cmd.CreateParameter();
cmd.Parameters.Add(parm);
parm.ParameterName = "@id";
parm.Value = attachment.Id;
cmd.CommandText = "select File from Attachment where Id = @id";
using (var reader = await cmd.ExecuteReaderAsync()){
if (await reader.ReadAsync())
await callback(reader.GetStream(0));
}
} finally {
await db.Database.CloseConnectionAsync();
}
}
public class AttachmentResult : FileStreamResult
{
private readonly DbContext db;
private readonly Attachment attachment;
public AttachmentResult(DbContext db, Attachment attachment) : base(new MemoryStream(), attachment.ContentType)
{
this.db = db;
this.attachment = attachment;
}
public override async Task ExecuteResultAsync(ActionContext context)
{
await Read(db, attachment, async s => {
FileStream = s;
await base.ExecuteResultAsync(context);
});
}
}
public static async Task Write(DbContext db, Attachment attachment, Stream content)
{
await db.Database.OpenConnectionAsync();
try {
var conn = db.Database.GetDbConnection();
var cmd = conn.CreateCommand();
cmd.Transaction = db.Database.CurrentTransaction?.GetDbTransaction();
var parm = cmd.CreateParameter();
cmd.Parameters.Add(parm);
parm.ParameterName = "@id";
parm.Value = attachment.Id;
parm = cmd.CreateParameter();
cmd.Parameters.Add(parm);
parm.ParameterName = "@content";
parm.Value = content;
cmd.CommandText = "update Attachment set File = @content where Id = @id";
await cmd.ExecuteNonQueryAsync();
} finally {
await db.Database.CloseConnectionAsync();
}
}
public static Task InsertAttachment(DbContext db, Attachment attachment, Stream content){
var strat = db.Database.CreateExecutionStrategy();
return strat.ExecuteAsync(async () => {
using (var trans = await db.Database.BeginTransactionAsync())
{
db.Set<Attachment>.Add(attachment);
await db.SaveChangesAsync();
await Write(db, attachment, content);
trans.Commit();
db.ChangeTracker.AcceptAllChanges();
}
});
}