Asp.net MVC源码分析--Model Validation(Server端)实现(2)

前面我们介绍了Model Validation的用法，以及ValidateModel的方法实现,这一篇我们来详细学习一下DataAnnotationsModelValidatorProvider类的实现。

上一篇:http://www.cnblogs.com/RobbinHan/archive/2011/12/15/2289228.html

三.DataAnnotationsModelValidatorProvider类详解

1.AttributeFactories对象

首先在这个类中可以看到在初始化时创建了AttributeFactories对象(Dictionary), 这个集合包含了系统内置一些验证规则。

internal static Dictionary<Type, DataAnnotationsModelValidationFactory> AttributeFactories = new Dictionary<Type, DataAnnotationsModelValidationFactory>() {
{
typeof(RangeAttribute),
(metadata, context, attribute) => new RangeAttributeAdapter(metadata, context, (RangeAttribute)attribute)
},
{
typeof(RegularExpressionAttribute),
(metadata, context, attribute) => new RegularExpressionAttributeAdapter(metadata, context, (RegularExpressionAttribute)attribute)
},
{
typeof(RequiredAttribute),
(metadata, context, attribute) => new RequiredAttributeAdapter(metadata, context, (RequiredAttribute)attribute)
},
{
typeof(StringLengthAttribute),
(metadata, context, attribute) => new StringLengthAttributeAdapter(metadata, context, (StringLengthAttribute)attribute)
},
}
}

2.ValidationAttribte 的 Adapter 设计模式应用

这里特别需要注意的是MVC利用了*AttributeAdapter 把 ValidationAttribte 的GetValidationResult方法和 ModelValidator.Validate方法作了一个适配(这里用到Adapter模式)请看RangeAttributeAdapter/RegularExpressionAttributeAdapter/RequiredAttributeAdapter/StringLengthAttributeAdapter

请参照DataAnnotationsModelValidator.Validate 方法源码,第7行代码，就是在这里进行了适配的工作。

public override IEnumerable<ModelValidationResult> Validate(object container) {
// Per the WCF RIA Services team, instance can never be null (if you have
// no parent, you pass yourself for the "instance" parameter).
ValidationContext context = new ValidationContext(container ?? Metadata.Model, null, null);
context.DisplayName = Metadata.GetDisplayName();

ValidationResult result = Attribute.GetValidationResult(Metadata.Model, context);
if (result != ValidationResult.Success) {
yield return new ModelValidationResult {
Message = result.ErrorMessage
};
}
}

3.获取ModelValidator对象集合

接下来我们来分析一下DataAnnotationsModelValidatorProvider.GetValidators 方法的实现

protected override IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context, IEnumerable<Attribute> attributes) {
_adaptersLock.EnterReadLock();

try {
List<ModelValidator> results = new List<ModelValidator>();

// Add an implied [Required] attribute for any non-nullable value type,
// unless they've configured us not to do that.
if (AddImplicitRequiredAttributeForValueTypes &&
metadata.IsRequired &&
!attributes.Any(a => a is RequiredAttribute)) {
attributes = attributes.Concat(new[] { new RequiredAttribute() });
}

// Produce a validator for each validation attribute we find
foreach (ValidationAttribute attribute in attributes.OfType<ValidationAttribute>()) {
DataAnnotationsModelValidationFactory factory;
if (!AttributeFactories.TryGetValue(attribute.GetType(), out factory)) {
factory = DefaultAttributeFactory;
}
results.Add(factory(metadata, context, attribute));
}

// Produce a validator if the type supports IValidatableObject
if (typeof(IValidatableObject).IsAssignableFrom(metadata.ModelType)) {
DataAnnotationsValidatableObjectAdapterFactory factory;
if (!ValidatableFactories.TryGetValue(metadata.ModelType, out factory)) {
factory = DefaultValidatableFactory;
}
results.Add(factory(metadata, context));
}

return results;
}
finally {
_adaptersLock.ExitReadLock();
}
}

我们看到从16-22行, MVC会从属性的Attributes中找到与AttributeFactories匹配的DataAnnotationsModelValidationFactory, 并调用返回ModelValidator对象，但如果没有从AttributeFactories找到匹配的对象，则使用DefaultAttributeFactory 委托创建一个ModelValidator对象。

DefaultAttributeFactory内部实现是创建一个DataAnnotationsModelValidator对象在构造时传入ValidationAttribute， 实际上这个类也是RangeAttributeAdapter等*AttributeAdapter类的基类，它们初始化的逻辑也是一样的。

internal static DataAnnotationsModelValidationFactory DefaultAttributeFactory =
(metadata, context, attribute) => new DataAnnotationsModelValidator(metadata, context, attribute);

4.IValidatableObject接口

最后我们看一下DataAnnotationsModelValidatorProvider.GetValidators 方法第25-30行代码.　

在这个方法中同样的我们发现MVC利用ValidatableObjectAdapter适配器连接ModelValidator.Validate方法 和 IValidatableObject.Validate接口.

BTW:利用[b]IValidatableObject接口可以实现验证模型的各个属性之间的逻辑关系.[/b]

可以参考另一篇文章:/article/5587517.html

总结:

Model Validatoin 可以通过在Modol属性上加入*ValidationAttribute 和 实现IValidatableObject 接口来进行验证

通过对DataAnnotationsModelValidatorProvider.GetValidators 方法的分析我们得出:
如果Model中的属性如果是复杂对象时，即使子对象中标记了*ValidationAttribute也是不会验证的。

例如下面的代码:LogOnModel.ChangePassword　对象中的属性虽然标记了[Required]但是还是不会验证的。

public class ChangePasswordModel
{
[Required]
[DataType(DataType.Password)]
[Display(Name = "Current password")]
public string OldPassword { get; set; }

[Required]
[ValidatePasswordLength]
[DataType(DataType.Password)]
[Display(Name = "New password")]
public string NewPassword { get; set; }

[DataType(DataType.Password)]
[Display(Name = "Confirm new password")]
[Compare("NewPassword", ErrorMessage = "The new password and confirmation password do not match.")]
public string ConfirmPassword { get; set; }
}

public class LogOnModel : IValidatableObject
{
[Required]
[Display(Name = "User name")]
public string UserName { get; set; }
[Required]
[Display(Name = "User age")]
public string Age { get; set; }
[Required]
[DataType(DataType.Password)]
[Display(Name = "Password")]
public string Password { get; set; }
[Display(Name = "Remember me?")]
public bool RememberMe { get; set; }
[Display(Name = "ChangePassword")]
//[Required]
public ChangePasswordModel ChangePassword { get; set; }

public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
return Enumerable.Empty<ValidationResult>();
}
}

疑问

另外有一点迷惑的是如果,如果把LogOnModel.ChangePassword属性是标记上[Required],而不从前台传入这个对象的话，所有LogOnModel属性上的验证都会失败，这一点不知道是不是Asp.net MVC 的bug,如果有人遇到请告诉我。

转载请注明出处:http://www.cnblogs.com/RobbinHan/archive/2011/12/15/2289403.html

本文作者: 十一月的雨 http://www.cnblogs.com/RobbinHan