I use the approach below to automatically copy data annotations from my entities to my view model. This ensures that things like StringLength and Required values are always the same for entity/viewmodel.
It works using the Automapper configuration, so works if the properties are named differently on the viewmodel as long as AutoMapper is setup correctly.
You need to create a custom ModelValidatorProvider and custom ModelMetadataProvider to get this to work. My memory on why is a little foggy, but I believe it's so both server and client side validation work, as well as any other formatting you do based on the metadata (eg an asterix next to required fields).
Note: I have simplified my code slightly as I added it below, so there may be a few small issues.
Metadata Provider
public class MetadataProvider : DataAnnotationsModelMetadataProvider
{
private IConfigurationProvider _mapper;
public MetadataProvider(IConfigurationProvider mapper)
{
_mapper = mapper;
}
protected override System.Web.Mvc.ModelMetadata CreateMetadata(IEnumerable<Attribute> attributes, Type containerType, Func<object> modelAccessor, Type modelType, string propertyName)
{
//Grab attributes from the entity columns and copy them to the view model
var mappedAttributes = _mapper.GetMappedAttributes(containerType, propertyName, attributes);
return base.CreateMetadata(mappedAttributes, containerType, modelAccessor, modelType, propertyName);
}
}
Validator Provivder
public class ValidatorProvider : DataAnnotationsModelValidatorProvider
{
private IConfigurationProvider _mapper;
public ValidatorProvider(IConfigurationProvider mapper)
{
_mapper = mapper;
}
protected override System.Collections.Generic.IEnumerable<ModelValidator> GetValidators(System.Web.Mvc.ModelMetadata metadata, ControllerContext context, IEnumerable<Attribute> attributes)
{
var mappedAttributes = _mapper.GetMappedAttributes(metadata.ContainerType, metadata.PropertyName, attributes);
return base.GetValidators(metadata, context, mappedAttributes);
}
}
Helper Method Referenced in above 2 classes
public static IEnumerable<Attribute> GetMappedAttributes(this IConfigurationProvider mapper, Type sourceType, string propertyName, IEnumerable<Attribute> existingAttributes)
{
if (sourceType != null)
{
foreach (var typeMap in mapper.GetAllTypeMaps().Where(i => i.SourceType == sourceType))
{
foreach (var propertyMap in typeMap.GetPropertyMaps())
{
if (propertyMap.IsIgnored() || propertyMap.SourceMember == null)
continue;
if (propertyMap.SourceMember.Name == propertyName)
{
foreach (ValidationAttribute attribute in propertyMap.DestinationProperty.GetCustomAttributes(typeof(ValidationAttribute), true))
{
if (!existingAttributes.Any(i => i.GetType() == attribute.GetType()))
yield return attribute;
}
}
}
}
}
if (existingAttributes != null)
{
foreach (var attribute in existingAttributes)
{
yield return attribute;
}
}
}
Other Notes
- If you're using dependency injection, make sure your container isn't already replacing the built in metadata provider or validator provider. In my case I was using the Ninject.MVC3 package which bound one of them after creating the kernel, I then had to rebind it afterwards so my class was actually used. I was getting exceptions about Required only being allowed to be added once, took most of a day to track it down.
