通过PicturreId获取图片路径(Url)

_pictureService.GetPictureUrl((int)entity.SponsorPictureId); //entity是具体查询出来的实体对象   SponsorPictureId是entity实体中的图片Id

string GetPictureUrl(int pictureId, 
            int targetSize = 0,
            bool showDefaultPicture = true, 
            string storeLocation = null, 
            PictureType defaultPictureType = PictureType.Entity);

 public virtual string GetPictureUrl(int pictureId,
            int targetSize = 0,
            bool showDefaultPicture = true,
            string storeLocation = null,
            PictureType defaultPictureType = PictureType.Entity)
        {
            var picture = GetPictureById(pictureId);//通过id得到一个对象
            return GetPictureUrl(picture, targetSize, showDefaultPicture, storeLocation, defaultPictureType);
        }

（2.2.1）GetPictureById方法

  public virtual Picture GetPictureById(int pictureId)
        {
            if (pictureId == 0)
                return null;

            return _pictureRepository.GetById(pictureId);
        }

 public virtual string GetPictureUrl(Picture picture,
            int targetSize = 0,
            bool showDefaultPicture = true,
            string storeLocation = null,
            PictureType defaultPictureType = PictureType.Entity)
        {
            string url = string.Empty;
            byte[] pictureBinary = null;
            if (picture != null)
                pictureBinary = LoadPictureBinary(picture);
            if (picture == null || pictureBinary == null || pictureBinary.Length == 0)
            {
                if (showDefaultPicture)
                {
                    url = GetDefaultPictureUrl(targetSize, defaultPictureType, storeLocation);
                }
                return url;
            }

            if (picture.IsNew)
            {
                DeletePictureThumbs(picture);

                //we do not validate picture binary here to ensure that no exception ("Parameter is not valid") will be thrown
                picture = UpdatePicture(picture.Id,
                    pictureBinary,
                    picture.MimeType,
                    picture.SeoFilename,
                    picture.AltAttribute,
                    picture.TitleAttribute,
                    false,
                    false);
            }

            var seoFileName = picture.SeoFilename; // = GetPictureSeName(picture.SeoFilename); //just for sure
            
            string lastPart = GetFileExtensionFromMimeType(picture.MimeType);
            string thumbFileName;
            if (targetSize == 0)
            {
                thumbFileName = !String.IsNullOrEmpty(seoFileName)
                    ? string.Format("{0}_{1}.{2}", picture.Id.ToString("0000000"), seoFileName, lastPart)
                    : string.Format("{0}.{1}", picture.Id.ToString("0000000"), lastPart);
            }
            else
            {
                thumbFileName = !String.IsNullOrEmpty(seoFileName)
                    ? string.Format("{0}_{1}_{2}.{3}", picture.Id.ToString("0000000"), seoFileName, targetSize, lastPart)
                    : string.Format("{0}_{1}.{2}", picture.Id.ToString("0000000"), targetSize, lastPart);
            }
            string thumbFilePath = GetThumbLocalPath(thumbFileName);

            //the named mutex helps to avoid creating the same files in different threads,
            //and does not decrease performance significantly, because the code is blocked only for the specific file.
            using (var mutex = new Mutex(false, thumbFileName))
            {
                if(!GeneratedThumbExists(thumbFilePath, thumbFileName))
                { 
                    mutex.WaitOne();

                    //check, if the file was created, while we were waiting for the release of the mutex.
                    if (!GeneratedThumbExists(thumbFilePath, thumbFileName))
                    {
                        byte[] pictureBinaryResized;

                        //resizing required
                        if (targetSize != 0)
                        {
                            using (var stream = new MemoryStream(pictureBinary))
                            {
                                Bitmap b = null;
                                try
                                {
                                    //try-catch to ensure that picture binary is really OK. Otherwise, we can get "Parameter is not valid" exception if binary is corrupted for some reasons
                                    b = new Bitmap(stream);
                                }
                                catch (ArgumentException exc)
                                {
                                    _logger.Error(string.Format("Error generating picture thumb. ID={0}", picture.Id),
                                        exc);
                                }

                                if (b == null)
                                {
                                    //bitmap could not be loaded for some reasons
                                    return url;
                                }

                                using (var destStream = new MemoryStream())
                                {
                                    var newSize = CalculateDimensions(b.Size, targetSize);
                                    ImageBuilder.Current.Build(b, destStream, new ResizeSettings
                                    {
                                        Width = newSize.Width,
                                        Height = newSize.Height,
                                        Scale = ScaleMode.Both,
                                        Quality = _mediaSettings.DefaultImageQuality
                                    });
                                    pictureBinaryResized = destStream.ToArray();
                                    b.Dispose();
                                }
                            }
                        }
                        else
                        {
                            //create a copy of pictureBinary
                            pictureBinaryResized = pictureBinary.ToArray();
                        }

                        SaveThumb(thumbFilePath, thumbFileName, picture.MimeType, pictureBinaryResized);
                    }
                    
                    mutex.ReleaseMutex();
                }
                
            }
            url = GetThumbUrl(thumbFileName, storeLocation);
            return url;//返回一个路径
        }