我正在尝试构建一个ASP.NET Core 1.1 Controller方法来处理如下所示的HTTP请求：
POST https://localhost/api/data/upload HTTP/1.1 Content-Type: multipart/form-data; boundary=--------------------------625450203542273177701444 Host: localhost Content-Length: 474 ----------------------------625450203542273177701444 Content-Disposition: form-data; name="file"; filename="myfile.txt" Content-Type: text/plain << Contents of my file >> ----------------------------625450203542273177701444 Content-Disposition: form-data; name="text" Content-Type: application/json {"md5":"595f44fec1e92a71d3e9e77456ba80d0","sessionIds":["123","abc"]} ----------------------------625450203542273177701444--
它是一个multipart / form-data请求,其中一部分是(小)文件,另一部分是基于提供的规范的json blob.
理想情况下,我喜欢我的控制器方法看起来像：
[HttpPost]
public async Task Post(UploadPayload payload)
{
// TODO
}
public class UploadPayload
{
public IFormFile File { get; set; }
[required]
[StringLength(32)]
public string Md5 { get; set; }
public List<string> SessionIds { get; set; }
}
但唉,这不是Just Work {TM}.当我这样时,IFormFile会填充,但json字符串不会反序列化到其他属性.
我还尝试向UploadPayload添加一个Text属性,该属性具有除IFormFile以外的所有属性,并且也不接收数据.例如.
public class UploadPayload
{
public IFormFile File { get; set; }
public UploadPayloadMetadata Text { get; set; }
}
public class UploadPayloadMetadata
{
[required]
[StringLength(32)]
public string Md5 { get; set; }
public List<string> SessionIds { get; set; }
}
我的解决方法是避免模型绑定并使用MultipartReader：
[HttpPost]
public async Task Post()
{
...
var reader = new MultipartReader(Request.GetMultipartBoundary(),HttpContext.Request.Body);
var section = await reader.ReadNextSectionAsync();
var filePart = section.AsFileSection();
// Do stuff & things with the file
section = await reader.ReadNextSectionAsync();
var jsonPart = section.AsFormDataSection();
var jsonString = await jsonPart.GetValueAsync();
// Use $JsonLibrary to manually deserailize into the model
// Do stuff & things with the Metadata
...
}
做上面的操作绕过了模型验证功能等.另外,我想也许我可以把那个jsonString然后以某种方式让它进入一个状态,然后我可以调用等待TryUpdateModelAsync(payloadModel,…)但是无法弄清楚如何到那儿 – 这似乎也没那么干净.
是否有可能像我的第一次尝试一样达到我想要的“透明”模型绑定状态？如果是这样,那怎么会这样呢？
解决方法
这里的第一个问题是数据需要以稍微不同的格式从客户端发送. UploadPayload类中的每个属性都需要以自己的形式发送：
const formData = new FormData();
formData.append(`file`,file);
formData.append('md5',JSON.stringify(md5));
formData.append('sessionIds',JSON.stringify(sessionIds));
执行此操作后,可以将[FromForm]属性添加到MD5属性以将其绑定,因为它是一个简单的字符串值.这不适用于SessionIds属性,因为它是一个复杂的对象.
可以使用自定义模型绑定器来完成从表单数据绑定复杂JSON：
public class FormDataJsonBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if(bindingContext == null) throw new ArgumentNullException(nameof(bindingContext));
// Fetch the value of the argument by name and set it to the model state
string fieldName = bindingContext.FieldName;
var valueProviderResult = bindingContext.ValueProvider.GetValue(fieldName);
if(valueProviderResult == ValueProviderResult.None) return Task.CompletedTask;
else bindingContext.ModelState.SetModelValue(fieldName,valueProviderResult);
// Do nothing if the value is null or empty
string value = valueProviderResult.FirstValue;
if(string.IsNullOrEmpty(value)) return Task.CompletedTask;
try
{
// Deserialize the provided value and set the binding result
object result = JsonConvert.DeserializeObject(value,bindingContext.ModelType);
bindingContext.Result = ModelBindingResult.Success(result);
}
catch(JsonException)
{
bindingContext.Result = ModelBindingResult.Failed();
}
return Task.CompletedTask;
}
}
然后,您可以在DTO类中使用ModelBinder属性来指示此绑定器应该用于绑定MyJson属性：
public class UploadPayload
{
public IFormFile File { get; set; }
[required]
[StringLength(32)]
[FromForm]
public string Md5 { get; set; }
[ModelBinder(BinderType = typeof(FormDataJsonBinder))]
public List<string> SessionIds { get; set; }
}
您可以在ASP.NET Core文档中阅读有关自定义模型绑定的更多信息：https://docs.microsoft.com/en-us/aspnet/core/mvc/advanced/custom-model-binding
