从 model class 以字节为单位从数据库检索图像到 IFormFile 的问题

Question

After creating a POST method for my API that allows me to upload images to the database where I hold them as bytes, I wanted to create a GET method that will allow me to get their information and eventually show them on a web page.

My model class looks like this:

public class Image
{
    public int recipeId { get; set; }
    public string format { get; set; }
    public string description { get; set; }
    public IFormFile image { get; set; }
}

IFormFile image is the image that gets uploaded from the front-end and gets converted using MemoryStream to fill the database like this:

This being said, below is my GET method:

[Route("v1/recipe/image/{recipeId}")]
[HttpGet()]
public Image GetImage(int recipeId)
{
    using (var con = _connFactory())
    {
        con.Open();
        return con.Query<Image>("SELECT * FROM RecipeImage WHERE RecipeId = @recipeId", new { recipeId }).FirstOrDefault();
    }
}

But I am getting the following error:

System.Data.DataException: 'Error parsing column 3 (Image=System.Byte[] - Object)'

InvalidCastException: Unable to cast object of type 'System.Byte[]' to type 'Microsoft.AspNetCore.Http.IFormFile'.

I understand what is going bad here, but I could not find any way around this. The only solution that I thought of was creating another model class for Image which instead of IFormFile has byte[] , but I was wondering if there's a better way of solving this problem.

Answer 1

That's because you can't cast a Byte array to IFormFile .

If you want to get an Image object, you'd first load the Byte array into a MemoryStream then call Image.FromMemoryStream(stream)

using (var ms = new MemoryStream(byteArrayIn))
{
    return Image.FromStream(ms);
}

You might want to consider adding an additional property into your model that returns the Image type, and load the value into it when the byte array is being set ie inside the setter for the byte[] .

public class Image
{
    public int recipeId { get; set; }
    public string format { get; set; }
    public string description { get; set; }
    private byte[] _image { get; set; }
    public byte[] image { get { return _image; } set { 
        _image = value; 
        using(var ms = new MemoryStream(byteArrayIn)) ...
            imageFile = Image.FromStream(ms);...
    }
    public Image imageFile { get; set; }
}

Answer 2

One way would be to map the properties manually

using (var con = _connFactory())
{
    con.Open();
    return con.Query("SELECT * FROM RecipeImage WHERE RecipeId = @recipeId", new { recipeId })
                .Select(x => new Image() 
                {
                    recipeId = x.RecipeId,
                    format = x.Format,
                    description = x.Description,
                    image = new FormFile(new MemoryStream(x.Image), 0, x.Image.Length, null, "MyFile." + x.Format, "")
                })
                .FirstOrDefault();
}

But probably you want to send the file alone if you want to display it on the web. Try navigating to the v1/recipe/image/xxx endpoint in the browser to see if the image loads.

[Route("v1/recipe/image/{recipeId}")]
[HttpGet()]
public async Task<IActionResult> GetImage(int recipeId)  
  {  
      var data = await con.QueryAsync<byte[]>("SELECT Image FROM RecipeImage WHERE RecipeId = @recipeId", new { recipeId }) 

      return File(new MemoryStream(data), "image/jpeg", "SomeName.jpg");  
  }