Add project files

T120B165-ImgBoard/Services/FileService.cs

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+using Microsoft.EntityFrameworkCore;
+using T120B165_ImgBoard.Data;
+using File = T120B165_ImgBoard.Models.File;
+
+namespace T120B165_ImgBoard.Services;
+
+public interface IFileService
+{
+    public Task<File?> GetFileById(long id);
+    Task<File> Update(File file);
+    Task Delete(File file);
+}
+
+public class FileService(ImgBoardContext context): IFileService
+{
+    public async Task<File?> GetFileById(long id)
+    {
+        return await context.Files.Where(f => f.Id == id).FirstOrDefaultAsync();
+    }
+
+    public async Task<File> Update(File file)
+    {
+        context.Files.Update(file);
+        await context.SaveChangesAsync();
+        return file;
+    }
+    
+    public async Task Delete(File file)
+    {
+        var actualFile = await GetFileById(file.Id);
+        context.Files.Remove(actualFile);
+        await context.SaveChangesAsync();
+    }
+}