如何为保存在数据库中的图像构造url

Question

我遇到了问题。我的数据库已正确配置，图像已正确保存在数据库中，但不知道如何为保存在数据库中的图像构造 url，因为我必须将其提供给敲除视图模型进行绑定。

  public JsonResult GetPosts()
    {
        var ret = (from post in db.Posts.ToList()
                   orderby post.PostedDate descending
                   select new
                   {
                       Message = post.Message,
                       PostedBy = post.PostedBy,
                       PostedByName = post.ApplicationUser.UserName,
 // having problem at this line dont know how to construct url at this line as i have to supply url
 // (String type to the PostedByAvatar)
                       PostedByAvatar = db.Files.SingleOrDefault(s => s.ApplicationUserId == post.PostedBy),
                       PostedDate = post.PostedDate,
                       PostId = post.PostId,
                   }).AsEnumerable();
        return Json(ret, JsonRequestBehavior.AllowGet);
    }

这是淘汰功能--------

    function Post(data) {
var self = this;
data = data || {};
self.PostId = data.PostId;
self.Message = ko.observable(data.Message || "");
self.PostedBy = data.PostedBy || "";
self.PostedByName = data.PostedByName || "";

self.PostedDate = getTimeAgo(data.PostedDate);
self.PostedByAvatar = data.PostedByAvatar || "";
self.error = ko.observable();
self.PostComments = ko.observableArray();

这是从数据库中获取现有帖子、评论等的视图模型-----

    function viewModel() {
    var self = this;
    self.posts = ko.observableArray();
    self.newMessage = ko.observable();
    self.error = ko.observable();
    self.loadPosts = function () {
        // to load existing posts
        $.ajax({
            url: postApiUrl1,
            datatype: "json",
            contentType: "application/json",
            cache: false,
            type: 'Get'
        })

在我的视图页面上，这是用于加载带有帖子的图像的容器框-----

    <ul id="msgHolder" data-bind="foreach: posts">
    <li class="postHolder">
    <img data-bind="attr: { src: PostedByAvatar }">
    <p><a data-bind="text: PostedByName"></a>: <span data-bind=" html: Message"></span></p>

现在，将图像保存在数据库中的模型类是这样的。它有ApplicationUserId作为指向ApplicationUserClass的外键---

   public class File
   {
    [Key]
    public int FileId { get; set; }
    [StringLength(255)]
    public string FileName { get; set; }
    [StringLength(100)]
    public string ContentType { get; set; }
    public byte[] Content { get; set; }
    public FileType FileType { get; set; }
    public int ApplicationUserId { get; set; }
    public virtual ApplicationUser ApplicationUser { get; set; }
   }

ApplicationUserClass 是这样的---

  public class ApplicationUser : IdentityUser<int, CustomUserLogin, CustomUserRole, CustomUserClaim>
   {
    public ApplicationUser()
    {
        this.Posts = new HashSet<Post>();
        this.Files = new HashSet<File>();
    }
    public virtual ICollection<File> Files { get; set; }
    public virtual ICollection<Post> Posts { get; set; }

这是保存在数据库中的图像。现在，我想知道如何为保存在数据库中的图像构造 url，因为我必须以字符串形式将其提供给视图模型。或者有比这更好的方法。

这是我的 Post 类，它与 ApplicationUser 类有多对一的关系，外键是 PostedBy 指向 ApplicationUser 类----

   public class Post
   {
    public Post()
    {
        this.PostComments = new HashSet<PostComment>();
    }
    [Key]
    public int PostId { get; set; }
    public string Message { get; set; }
    public int? PostedBy { get; set; }
    public System.DateTime PostedDate { get; set; }
    public virtual ICollection<PostComment> PostComments { get; set; }
    public virtual ApplicationUser ApplicationUser { get; set; }
}

Answer 1

虽然可以将 Base64 字符串作为 src 的 src 传递，但我认为最明智的方法是不从 Ajax 调用返回实际字节，而是创建一个请求来自服务器的图像字节。

首先，添加将提供图像数据所需的操作：

[HttpGet]
public FileResult GetFileData(int fileId)
{
    var file = db.Files.Single(x => x.FileId == fileId);

    return File(file.Content, file.ContentType);
}

现在，将您的 GetPosts 操作更改为在 PostedByAvatar 属性中返回 url：

public JsonResult GetPosts()
{
    var ret = (from post in db.Posts.ToList()
               orderby post.PostedDate descending)
               select new
               {
                   Message = post.Message,
                   PostedBy = post.PostedBy,
                   PostedByName = post.ApplicationUser.UserName,
                   PostedByAvatar = _GenerateAvatarUrlForUser(post.PostedBy),
                   PostedDate = post.PostedDate,
                   PostId = post.PostId,
               });

    return Json(ret, JsonRequestBehavior.AllowGet);
}

private string _GenerateAvatarUrlForUser(int? userId)
{
    if (!user.HasValue)
        return null;

    var avatarImage = db.Files.SingleOrDefault(s => s.ApplicationUserId == userId);

    if (avatarImage != null)
        return Url.Action("GetFileData", new { fileId = avatarImage.FileId });

    return null;
}