I've found a lot of information on implementing a custom model binder for validation purposes but I haven't seen much about what I'm attempting to do.
I want to be able to manipulate the values that the model binder is going to set based on attributes on the property in the view model. For instance:
public class FooViewModel : ViewModel
{
[AddBar]
public string Name { get; set; }
}
AddBar is just
public class AddBarAttribute : System.Attribute
{
}
I've not been able to find a clean way to find the attributes on a view model property in the custom model binder's BindModel method. This works but it feels like there should be a simpler solution:
public class FooBarModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var value = base.BindModel(controllerContext, bindingContext);
var hasBarAttribute = false;
if(bindingContext.ModelMetadata.ContainerType != null)
{
var property = bindingContext.ModelMetadata.ContainerType.GetProperties()
.Where(x => x.Name == bindingContext.ModelMetadata.PropertyName).FirstOrDefault();
hasBarAttribute = property != null && property.GetCustomAttributes(true).Where(x => x.GetType() == typeof(AddBarAttribute)).Count() > 0;
}
if(value.GetType() == typeof(String) && hasBarAttribute)
value = ((string)value) + "Bar";
return value;
}
}
Is there a cleaner way to view the attributes on the view model property or a different kind of attribute I could be using? The DataAnnotation attributes really seem to be for a different problem.
UPDATE
Craig's answer got me to the right place but I thought I'd put some examples in here for others.
The metadata provider I ended up with looks like
public class FooBarModelMetadataProvider : DataAnnotationsModelMetadataProvider
{
protected override ModelMetadata CreateMetadata(IEnumerable<Attribute> attributes, Type containerType, Func<object> modelAccessor, Type modelType, string propertyName)
{
var metaData = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);
if(attributes.OfType<AddBarAttribute>().Any())
metaData.AdditionalValues.Add("AddBarKey", true);
return metaData;
}
}
The model binder looks like:
public class FooBarModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var value = base.BindModel(controllerContext, bindingContext);
if(bindingContext.ModelMetadata.AdditionalValues.ContainsKey("AddBarKey"))
value = ((string)value) + "Bar";
return value;
}
}
The "correct" way (per the guy who wrote it) is to write a model metadata provider. There's an example at the link. Not precisely "simple," but it works, and you'll be doing what the rest of MVC does.
Related
I know how to create a model class that mirrors query string variables so that when it comes into my Web API controller action, the model is populated.
However, is there a way to make it so that I'm not locked into the query string variable names as the properties on my model class?
Example:
public class MyModel {
public string o {get;set;}
}
public class MyController {
public string Get(MyModel model) {
}
}
Then, if my query string looks like:
GET http://domain.com/?o=12345
Is there a way to name that model property "Order" or something instead of "o" and then have it populated with the value from "o="?
You can create custom model binder that will bind data to model as you wish. To use it you should:
public string Get([ModelBinder(typeof(MyComplexTypeModelBinder))]MyModel model)
{
...
}
To create custom model binder you can inherit from IModelBinder or from DefaultModelBinder.
public class MyComplexTypeModelBinder : IModelBinder
{
public Object BindModel(ControllerContext controllerContext,
ModelBindingContext bindingContext)
{
if (bindingContext == null)
throw new ArgumentNullException("bindingContext");
// Create the model instance (using the ctor you like best)
var obj = new MyComplexType();
// Set properties reading values from registered value providers
obj.Order = FromPostedData<string>(bindingContext, "o");
...
return obj;
}
private T FromPostedData<T>(ModelBindingContext context, String key)
{
// Get the value from any of the input collections
ValueProviderResult result;
context.ValueProvider.TryGetValue(key, out result);
// Set the state of the model property resulting from
context.ModelState.SetModelValue(key, result);
// Return the value converted (if possible) to the target type
return (T) result.ConvertTo(typeof(T));
}
Solution for this scenario is custom IValueProvider. This ASP.NET MVC extension point is the correct place, where we can bridge the QueryString keys into Model.Property names. In comparison with ModelBinder, this will target exactly what we need (while not introducing later issues, when even other value providers (FORM) accidently contains that key...)
There is good tutorial how to introduce the custom IValueProvider:
http://donovanbrown.com/post/How-to-create-a-custom-Value-Provider-for-MVC.aspx
And there is an simple example which is able to provide values for Model "Order" property, coming as QueryString "o" key:
Factory
// Factory
public class MyValueProviderFactory : ValueProviderFactory
{
public override IValueProvider GetValueProvider(ControllerContext ctx)
{
return new MyValueProvider(ctx);
}
}
Provider
// Provider
class MyValueProvider : IValueProvider
{
protected HttpRequestBase Request { get; set; }
public MyValueProvider(ControllerContext ctx)
{
Request = ctx.HttpContext.Request;
}
// our custom logic to test QueryString keys, and expected prefixes
public bool ContainsPrefix(string prefix)
{
var containsSpecial =
"Order".Equals(prefix, StringComparison.OrdinalIgnoreCase)
&& Request.QueryString.AllKeys.Contains("o"
, StringComparer.InvariantCultureIgnoreCase);
return containsSpecial;
}
// Handling "Order" key
public ValueProviderResult GetValue(string key)
{
if (!ContainsPrefix(key))
{
return null;
}
var values = Request.QueryString.GetValues("o");
if (values.Any())
{
return new ValueProviderResult(values, values.First()
, CultureInfo.CurrentCulture);
}
return null;
}
}
And in the global.asax we have to inject it:
protected void Application_Start()
{
ValueProviderFactories.Factories.Add(new MyValueProviderFactory());
...
We know that MVC returns DateTime for JsonResult in this format: /Date(1240718400000)/, and we know how to parse it in JS.
However, It seems that MVC doesn't accept DateTime parameter being sent in this way. For example, I have the following Action.
[HttpGet]
public ViewResult Detail(BookDetail details) { //... }
The BookDetail class contains a DateTime field named CreateDate, and I passed a JSON object from JS in this format:
{"CreateDate": "/Date(1319144453250)/"}
CreateDate is recognized as null.
If I passed the JSON in this way, it works as expected:
{"CreateDate": "2011-10-10"}
The problem is that I cannot change client side code in an easy way, have to stick to /Date(1319144453250)/ this format. I have to make changes in server side.
How to solve this problem? Is that anything related to ModelBinder?
Thanks so much in advance!
The problem, as you suspected, is a model binding issue.
To work around it, create a custom type, and let's call it JsonDateTime. Because DateTime is a struct, you cannot inherit from it, so create the following class:
public class JsonDateTime
{
public JsonDateTime(DateTime dateTime)
{
_dateTime = dateTime;
}
private DateTime _dateTime;
public DateTime Value
{
get { return _dateTime; }
set { _dateTime = value; }
}
}
Change CreateDate to this type. Next, we need a custom model binder, like so:
public class JsonDateTimeModelBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName).ToString();
return new DateTime(Int64.Parse(
value.Substring(6).Replace(")/",String.Empty))); // "borrowed" from skolima's answer
}
}
Then, in Global.asax.cs, in Application_Start, register your custom ModelBinder:
ModelBinders.Binders.Add(typeof(JsonDateTime), new JsonDateTimeModelBinder());
In your model, use this to parse the date:
// property
String CreateDate;
DateTime CreateDateAsDate;
// drop prefix, drop suffix, parse as long and read as ticks
CreateDateAsDate date = new DateTime(Int64.Parse(
CreateDate.Substring(6).Replace(")/",String.Empty)));
I think using custom Model Binder will do the trick. The below model binder class will work on both cases. It will parse all dot net recognizable date string as well as JSON formatted date string. No need to change any existing code.
public class DateTimeModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var model = base.BindModel(controllerContext, bindingContext);
if (model == null && (bindingContext.ModelType == typeof(DateTime) || bindingContext.ModelType == typeof(DateTime?)))
{
var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
if (value == null || String.IsNullOrEmpty(value.AttemptedValue))
model = (bindingContext.ModelType == typeof(DateTime?)) ? null : (object)DateTime.MinValue;
else if (Regex.IsMatch(value.AttemptedValue, #"\/Date\(\d+\)\/"))
model = new DateTime(1970, 1, 1).AddMilliseconds(Int64.Parse(value.AttemptedValue.Substring(6).Replace(")/", String.Empty))).ToLocalTime();
//else //Any other format
}
return model;
}
}
Configure Model Binder in Application_Start of Global.asax
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
//Your Existing Code....
ModelBinders.Binders.Add(typeof(DateTime), new DateTimeModelBinder());
ModelBinders.Binders.Add(typeof(DateTime?), new DateTimeModelBinder());
}
}
Vote If it helps
I would like to be able to post any serialized object to an action method and instantiate a new object of the posted type in order to use TryUpdateModel. They didn't teach me any of this stuff in the QBasic help file... How can I instantiate the unknown type based on the posted data?
If it would help, I could theoretically include the name of the type as a string in the posted data. I was hoping to avoid that because it seemed like I would need the full name of the type.
public void Save(object/dynamic whatever, string typename) {
//Instantiate posted type
//TryUpdateModel
context.Entry(Thing).State = EntityState.Modified;
context.SaveChanges();
}
Here is an example of a serialized object
Thing.Id=1&Thing.Name=blah&Thing.OptionID=1&Thing.ListItems.index=1&Thing.ListItems%5B1%5D.Id=1&Thing.ListItems%5B1%5D.Name=whatever&Thing.ListItems%5B1%5D.OptionID=2&Thing.ListItems%5B1%5D.ThingID=1&Thing.ListItems%5B1%5D.EntityState=16
From Fiddler
Thing.Id 1
Thing.Name blah
Thing.OptionID 1
Thing.ListItems.index 1
Thing.ListItems[1].Id 1
Thing.ListItems[1].Name whatever
Thing.ListItems[1].OptionID 2
Thing.ListItems[1].ThingID 1
Thing.ListItems[1].EntityState 16
You could write a custom model binder which uses reflection and the typeName parameter:
public class MyModelBinder : DefaultModelBinder
{
protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
{
var typeValue = bindingContext.ValueProvider.GetValue("typename");
if (typeValue == null)
{
throw new Exception("Impossible to instantiate a model. The \"typeName\" query string parameter was not provided.");
}
var type = Type.GetType(
(string)typeValue.ConvertTo(typeof(string)),
true
);
var model = Activator.CreateInstance(type);
bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, type);
return model;
}
}
and then simply:
[HttpPost]
public ActionResult Save([ModelBinder(typeof(MyModelBinder))] object model)
{
context.Entry(model).State = EntityState.Modified;
context.SaveChanges();
return View();
}
I have a few questions regarding custom model binding, model state, and data annotations.
1) Is it redundant to do validation in the custom model binder if I have data annotations on my model, because that's what I thought the point of data annotations were.
2) Why is my controller treating the model state as valid even when it's not, mainly I make the Name property null or too short.
3) Is it ok to think of custom model binders as constructor methods, because that's what they remind me of.
First here is my model.
public class Projects
{
[Key]
[Required]
public Guid ProjectGuid { get; set; }
[Required]
public string AccountName { get; set; }
[Required(ErrorMessage = "Project name required")]
[StringLength(128, ErrorMessage = "Project name cannot exceed 128 characters")]
[MinLength(3, ErrorMessage = "Project name must be at least 3 characters")]
public string Name { get; set; }
[Required]
public long TotalTime { get; set; }
}
Then I'm using a custom model binder to bind some properties of the model. Please don't mind that it's quick and dirty just trying to get it functioning and then refactoring it.
public class ProjectModelBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
if (controllerContext == null)
{
throw new ArgumentNullException("controllerContext");
}
if (bindingContext == null)
{
throw new ArgumentNullException("bindingContext");
}
var p = new Project();
p.ProjectGuid = System.Guid.NewGuid();
p.AccountName = controllerContext.HttpContext.User.Identity.Name;
p.Name = controllerContext.HttpContext.Request.Form.Get("Name");
p.TotalTime = 0;
//
// Is this redundant because of the data annotations?!?!
//
if (p.AccountName == null)
bindingContext.ModelState.AddModelError("Name", "Name is required");
if (p.AccountName.Length < 3)
bindingContext.ModelState.AddModelError("Name", "Minimum length is 3 characters");
if (p.AccountName.Length > 128)
bindingContext.ModelState.AddModelError("Name", "Maximum length is 128 characters");
return p;
}
}
Now my controller action.
[HttpPost]
public ActionResult CreateProject([ModelBinder(typeof(ProjectModelBinder))]Project project)
{
//
// For some reason the model state comes back as valid even when I force an error
//
if (!ModelState.IsValid)
return Content(Boolean.FalseString);
//_projectRepository.CreateProject(project);
return Content(Boolean.TrueString);
}
EDIT
I Found some code on another stackoverflow question but I'm not sure at which point I would inject the following values into this possible solution.
What I want to inject when a new object is created:
var p = new Project();
p.ProjectGuid = System.Guid.NewGuid();
p.AccountName = controllerContext.HttpContext.User.Identity.Name;
p.Name = controllerContext.HttpContext.Request.Form.Get("Name");
p.TotalTime = 0;
How do I get the above code into what's below (Possible solution):
public class ProjectModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
if (bindingContext.ModelType == typeof(Project))
{
ModelBindingContext newBindingContext = new ModelBindingContext()
{
ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(
() => new Project(), // construct a Project object,
typeof(Project) // using the Project metadata
),
ModelState = bindingContext.ModelState,
ValueProvider = bindingContext.ValueProvider
};
// call the default model binder this new binding context
return base.BindModel(controllerContext, newBindingContext);
}
else
{
return base.BindModel(controllerContext, bindingContext);
}
}
}
}
You will find things work much easier if you inherit from the DefaultModelBinder, override the BindModel method, call the base.BindModel method and then make the manual changes (setting the guid, account name and total time).
1) It is redundant to validate as you have done it. You could write code to reflect the validation metadata much like the default does, or just remove the data annotations validation since you are not using it in your model binder.
2) I don't know, it seems correct, you should step through the code and make sure your custom binder is populating all of the applicable rules.
3) It's a factory for sure, but not so much a constructor.
EDIT: you couldn't be any closer to the solution, just set the properties you need in the model factory function
public class ProjectModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
if (bindingContext.ModelType == typeof(Project))
{
ModelBindingContext newBindingContext = new ModelBindingContext()
{
ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(
() => new Project() // construct a Project object
{
ProjectGuid = System.Guid.NewGuid(),
AccountName = controllerContext.HttpContext.User.Identity.Name,
// don't set name, thats the default binder's job
TotalTime = 0,
},
typeof(Project) // using the Project metadata
),
ModelState = bindingContext.ModelState,
ValueProvider = bindingContext.ValueProvider
};
// call the default model binder this new binding context
return base.BindModel(controllerContext, newBindingContext);
}
else
{
return base.BindModel(controllerContext, bindingContext);
}
}
}
Or you could alternately override the CreateModel method:
protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, System.Type modelType)
{
if (modelType == typeof(Project))
{
Project model = new Project()
{
ProjectGuid = System.Guid.NewGuid(),
AccountName = controllerContext.HttpContext.User.Identity.Name,
// don't set name, thats the default binder's job
TotalTime = 0,
};
return model;
}
throw new NotSupportedException("You can only use the ProjectModelBinder on parameters of type Project.");
}
I would like to write my own model binder for DateTime type. First of all I'd like to write a new attribute that I can attach to my model property like:
[DateTimeFormat("d.M.yyyy")]
public DateTime Birth { get; set,}
This is the easy part. But the binder part is a bit more difficult. I would like to add a new model binder for type DateTime. I can either
implement IModelBinder interface and write my own BindModel() method
inherit from DefaultModelBinder and override BindModel() method
My model has a property as seen above (Birth). So when the model tries to bind request data to this property, my model binder's BindModel(controllerContext, bindingContext) gets invoked. Everything ok, but. How do I get property attributes from controller/bindingContext, to parse my date correctly? How can I get to the PropertyDesciptor of property Birth?
Edit
Because of separation of concerns my model class is defined in an assembly that doesn't (and shouldn't) reference System.Web.MVC assembly. Setting custom binding (similar to Scott Hanselman's example) attributes is a no-go here.
you can change the default model binder to use the user culture using IModelBinder
public class DateTimeBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
bindingContext.ModelState.SetModelValue(bindingContext.ModelName, value);
return value.ConvertTo(typeof(DateTime), CultureInfo.CurrentCulture);
}
}
public class NullableDateTimeBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
bindingContext.ModelState.SetModelValue(bindingContext.ModelName, value);
return value == null
? null
: value.ConvertTo(typeof(DateTime), CultureInfo.CurrentCulture);
}
}
And in the Global.Asax add the following to Application_Start():
ModelBinders.Binders.Add(typeof(DateTime), new DateTimeBinder());
ModelBinders.Binders.Add(typeof(DateTime?), new NullableDateTimeBinder());
Read more at this excellent blog that describe why Mvc framework team implemented a default Culture to all users.
I had this very big problem myself and after hours of try and fail I got a working solution like you asked.
First of all since having a binder on just a property is not possibile yuo have to implement a full ModelBinder. Since you don't want the bind all the single property but only the one you care you can inherit from DefaultModelBinder and then bind the single property:
public class DateFiexedCultureModelBinder : DefaultModelBinder
{
protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
{
if (propertyDescriptor.PropertyType == typeof(DateTime?))
{
try
{
var model = bindingContext.Model;
PropertyInfo property = model.GetType().GetProperty(propertyDescriptor.Name);
var value = bindingContext.ValueProvider.GetValue(propertyDescriptor.Name);
if (value != null)
{
System.Globalization.CultureInfo cultureinfo = new System.Globalization.CultureInfo("it-CH");
var date = DateTime.Parse(value.AttemptedValue, cultureinfo);
property.SetValue(model, date, null);
}
}
catch
{
//If something wrong, validation should take care
}
}
else
{
base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
}
}
}
In my example I'm parsing date with a fiexed culture, but what you want to do is possible. You should create a CustomAttribute (like DateTimeFormatAttribute) and put it over you property:
[DateTimeFormat("d.M.yyyy")]
public DateTime Birth { get; set,}
Now in the BindProperty method, instead of looking for a DateTime property you can look for a property with you DateTimeFormatAttribute, grab the format you specified in the constructor and then parse the date with DateTime.ParseExact
I hope this helps, it took me very long to come with this solution. It was actually easy to have this solution once I knew how to search it :(
I don't think you should put locale-specific attributes on a model.
Two other possible solutions to this problem are:
Have your pages transliterate dates from the locale-specific format to a generic format such as yyyy-mm-dd in JavaScript. (Works, but requires JavaScript.)
Write a model binder which considers the current UI culture when parsing dates.
To answer your actual question, the way to get custom attributes (for MVC 2) is to write an AssociatedMetadataProvider.
You could implement a custom DateTime Binder like so, but you have to take care about the assumed culture and value from the actual client request. May you get an Date like mm/dd/yyyy in en-US and want it to convert in the systems culture en-GB (which it would be like dd/mm/yyyy) or an invariant culture, like we do, then you have to parse it before and using the static facade Convert to change it in its behaviour.
public class DateTimeModelBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var valueResult = bindingContext.ValueProvider
.GetValue(bindingContext.ModelName);
var modelState = new ModelState {Value = valueResult};
var resDateTime = new DateTime();
if (valueResult == null) return null;
if ((bindingContext.ModelType == typeof(DateTime)||
bindingContext.ModelType == typeof(DateTime?)))
{
if (bindingContext.ModelName != "Version")
{
try
{
resDateTime =
Convert.ToDateTime(
DateTime.Parse(valueResult.AttemptedValue, valueResult.Culture,
DateTimeStyles.AdjustToUniversal).ToUniversalTime(), CultureInfo.InvariantCulture);
}
catch (Exception e)
{
modelState.Errors.Add(EnterpriseLibraryHelper.HandleDataLayerException(e));
}
}
else
{
resDateTime =
Convert.ToDateTime(
DateTime.Parse(valueResult.AttemptedValue, valueResult.Culture), CultureInfo.InvariantCulture);
}
}
bindingContext.ModelState.Add(bindingContext.ModelName, modelState);
return resDateTime;
}
}
Anyway, culture dependend DateTime parsing in a stateless Application can by a cruelty...Especially when you work with JSON on javascript clientside and backwards.