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IValidatableObject接口可以实现验证模型的各个属性之间的逻辑关系.

 可以参考另一篇文章:http://www.cnblogs.com/bjs007/archive/2011/01/27/1946419.html

总结:

1. 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
2. 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