在EF Core中填充没有关系的单独表

Question

我需要添加图片并将图片ID和产品ID存储在单独的productPicture表中。没有现有产品，您无法添加图片。如何实现呢？

这是我向数据库添加实体的代码：

控制器：

 [HttpPost]
    [Route("api/v1/catalog/products/pictures")]
    [ProducesResponseType((int)HttpStatusCode.Created)]
    [ProducesResponseType((int)HttpStatusCode.BadRequest)]
    public async Task<IActionResult> UploadPicture([FromForm]PictureViewModel pic)
    {
        try
        {
            var result = await _service.Add(pic);

            if (result.HasErrors)
            {
                return BadRequest(result.Errors);
            }

            return CreatedAtAction(nameof(GetById), result);
        }
        catch (Exception ex)
        {
            return BadRequest(ex.ToString());
        }
    }

服务：

        public async Task<ServiceResultWithoutBaseEntity<Picture>> Add(PictureViewModel newItem)
    {
        var result = new ServiceResultWithoutBaseEntity<Picture>();
        result.Errors.AddRange(Validate(newItem));

        if (result.HasErrors)
            return result;

        var item = await newItem.MapToEntity(new Picture());

        _context.Pictures.Add(item);
        await _context.SaveChangesAsync();

        result.EntityResult = item;

        return result;
    }

助手：

        public async static Task<Picture> MapToEntity(this PictureViewModel source, Picture entity)
    {
        if (source == null || entity == null)
            return null;

        if (source.FileForUpload != null || source.FileForUpload.Length != 0)
        {
            AzureBlobExtensions abe = new AzureBlobExtensions();
            string folderValue = string.Concat(entity.ID.ToString().ToLower(), "/", DateTime.Now.ToString("yyyyMMddHHmmss"), source.FileForUpload.FileName);
            var fileUrl = await abe.UploadFile(source.FileForUpload, folderValue, Path.GetExtension(source.FileForUpload.FileName), "Picture");
            entity.VirtualPath = fileUrl;
        }
        else
        {
            entity.VirtualPath = source.FileUrl;
        }

        entity.FileName = source.FileName;
        entity.SeoFilename = source.SeoFilename;
        entity.AltAttribute = source.AltAttribute;
        entity.TitleAtrribute = source.TitleAtrribute;
        entity.MimeType = source.MimeType;
        entity.IsNew = source.IsNew;

        return entity;
    }

产品表

图片表

productPicture表