我正在尝试在ASP.NET Core MVC Web应用程序中实现我的自定义验证属性，包括服务器和客户端验证。现有数据注释的缺点是属性的静态性质，这使得无法将运行时数据传递给它。
我想制作GreaterThanAttribute，它将另一个属性的名称作为参数，以将给定值与该属性的值进行比较。像这样的东西：
public class TestModel
{
public int PropertyA { get; set; }
[GreaterThan(nameof(PropertyA))]
public int PropertyB { get; set; }
}
我已经通过以下方式实现了该属性：
[AttributeUsage(AttributeTargets.Property)]
public class GreaterThanAttribute : ValidationAttribute, IClientModelValidator
{
public const string RuleName = "greaterthan";
public const string ParameterName = "othervalue";
public object OtherPropertyValue { get; set; }
public string OtherPropertyName { get; }
public GreaterThanAttribute(string otherPropertyName)
{
OtherPropertyName = otherPropertyName;
ErrorMessage = $"The value should be greater than filed {OtherPropertyName}";
}
public void AddValidation(ClientModelValidationContext context)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
MergeAttribute(context.Attributes, "data-val", "true");
MergeAttribute(context.Attributes, $"data-val-{RuleName}", ErrorMessageString);
MergeAttribute(context.Attributes, $"data-val-{RuleName}-{ParameterName}", OtherPropertyValue?.ToString());
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
// server side validation, no difficulties here
}
private static void MergeAttribute(IDictionary<string, string> attributes, string key, string value)
{
if (attributes.ContainsKey(key))
return;
attributes.Add(key, value);
}
}
我在我的视图中为此属性添加了醒目的验证器：
<script type="text/javascript">
$.validator.addMethod("@GreaterThanAttribute.RuleName", function (value, element, params) {
var parsedThisValue = Globalize.numberParser()(value);
var parsedOtherValue = Globalize.numberParser()(params);
return parsedThisValue > parsedOtherValue;
});
$.validator.unobtrusive.adapters.addSingleVal("@GreaterThanAttribute.RuleName", "@GreaterThanAttribute.ParameterName");
</script>
问题是，现在我需要手动将data-val-greaterthan-othervalue属性添加到输入字段，例如：
@{
var propertyName = $"data-val-{GreaterThanAttribute.RuleName}-{GreaterThanAttribute.ParameterName}";
var propertyValue = Model.Child[0].PropertyB;
}
@Html.TextBoxFor(x => Model.Child[0].PropertyA, new Dictionary<string, object> {{propertyName, propertyValue}})
@Html.ValidationMessageFor(x => Model.Child[0].PropertyA)
而且我不喜欢那样。因此，我正在寻找一种使用现有ASP.NET机制添加此属性而又不会污染其视图的方法。与我在答案Access model data in AddValidation method asp.net core custom validation中找到的最接近的方法。
现在我正在尝试将实际值注入到我的自定义验证html属性提供程序中的属性中：
public class CustomValidationHtmlAttributeProvider : DefaultValidationHtmlAttributeProvider
{
private readonly IOptions<MvcViewOptions> _optionsAccessor;
private readonly IModelMetadataProvider _metadataProvider;
private readonly ClientValidatorCache _clientValidatorCache;
public CustomValidationHtmlAttributeProvider(IOptions<MvcViewOptions> optionsAccessor, IModelMetadataProvider metadataProvider, ClientValidatorCache clientValidatorCache)
: base(optionsAccessor, metadataProvider, clientValidatorCache)
{
_optionsAccessor = optionsAccessor;
_metadataProvider = metadataProvider;
_clientValidatorCache = clientValidatorCache;
}
public override void AddValidationAttributes(ViewContext viewContext, ModelExplorer modelExplorer, IDictionary<string, string> attributes)
{
// getting existing validation attribute
var greaterThanAttribute = modelExplorer.Metadata.ValidatorMetadata.FirstOrDefault(x =>
x.GetType() == typeof(GreaterThanAttribute)) as GreaterThanAttribute;
var otherPropertyName = greaterThanAttribute.OtherPropertyName;
// -------------
// how to get reference to parent object of the model here?
// -------------
var otherValue = ?????????????
greaterThanAttribute.OtherPropertyValue = otherValue;
base.AddValidationAttributes(viewContext, modelExplorer, attributes);
}
}
问题是我找不到一种方法来获取对正在验证的属性的父类的引用，以获取PropertyB的值。我这里只有：
modelExplorer.Model指向PropertyA的值，按预期方式modelExplorer.Container指向一个视图的整个模型的值，这很复杂，可能具有多个层次结构和列表。因此，基本上我现在需要立即获取Model.Child[0].PropertyA的值，但我事先不知道确切的路径。当然，我不知道当前Child的索引，等等。modelExplorer.Metadata具有用于整个容器的当前属性的所有元数据，但是我看不到将此元数据连接到实际Model和值的方法。所以问题是：考虑到我不了解容器的整个层次结构这一事实，如何在这里达到PropertyB的值？也许还有完成所需验证属性的其他完整方法？
我终于找到了解决方案。
首先，我已重载了错误版本的方法。正确的是void AddAndTrackValidationAttributes(ViewContext viewContext, ModelExplorer modelExplorer, string expression, IDictionary<string, string> attributes)，因为它为具有验证属性的当前属性提供了表达式字符串。
使用此表达式，我们可以假定名称存储在otherPropertyName中的目标属性存在于同一路径上（因为它位于同一类中）。例如，如果表达式为Model.Child[0].PropertyA，则可以使用表达式Model.Child[0].PropertyB检索目标属性。
[不幸的是，ExpressionMetadataProvider.FromStringExpression函数不适用于使用索引器进行表达。但是，它仅适用于属性表达式。就我而言，唯一的方法是手动遍历对象层次结构：解析表达式并使用反射进入给定索引处的属性和元素。
整个代码：
public class CustomValidationHtmlAttributeProvider : DefaultValidationHtmlAttributeProvider
{
private readonly IOptions<MvcViewOptions> _optionsAccessor;
private readonly IModelMetadataProvider _metadataProvider;
private readonly ClientValidatorCache _clientValidatorCache;
public CustomValidationHtmlAttributeProvider(IOptions<MvcViewOptions> optionsAccessor, IModelMetadataProvider metadataProvider, ClientValidatorCache clientValidatorCache)
: base(optionsAccessor, metadataProvider, clientValidatorCache)
{
_optionsAccessor = optionsAccessor;
_metadataProvider = metadataProvider;
_clientValidatorCache = clientValidatorCache;
}
public override void AddValidationAttributes(ViewContext viewContext, ModelExplorer modelExplorer, string expression, IDictionary<string, string> attributes)
{
// getting existing validation attribute
var greaterThanAttribute = modelExplorer.Metadata.ValidatorMetadata.FirstOrDefault(x =>
x.GetType() == typeof(GreaterThanAttribute)) as GreaterThanAttribute;
var otherPropertyName = greaterThanAttribute.OtherPropertyName;
var targetExpression = GetTargetPropertyExpression(expression, otherPropertyName);
var otherValue = GetValueOnExpression(modelExplorer.Container.Model, targetExpression);
greaterThanAttribute.OtherPropertyValue = otherValue;
base.AddValidationAttributes(viewContext, modelExplorer, attributes);
}
private static object GetValueOnExpression(object container, string expression)
{
while (expression != "")
{
if (NextStatementIsIndexer(expression))
{
var index = GetIndex(expression);
switch (container)
{
case IDictionary dictionary:
container = dictionary[index];
break;
case IEnumerable<object> enumerable:
container = enumerable.ElementAt(int.Parse(index));
break;
default:
throw new Exception($"{container} is unknown collection type");
}
expression = ClearIndexerStatement(expression);
}
else
{
var propertyName = GetPropertyStatement(expression);
var propertyInfo = container.GetType().GetProperty(propertyName);
if (propertyInfo == null)
throw new Exception($"Can't find {propertyName} property in the container {container}");
container = propertyInfo.GetValue(container);
expression = ClearPropertyStatement(expression);
}
}
return container;
}
private static bool NextStatementIsIndexer(string expression)
=> expression[0] == '[';
private static string ClearPropertyStatement(string expression)
{
var statementEndPosition = expression.IndexOfAny(new [] {'.', '['});
if (statementEndPosition == -1) return "";
if (expression[statementEndPosition] == '.') statementEndPosition++;
return expression.Substring(statementEndPosition);
}
private static string GetPropertyStatement(string expression)
{
var statementEndPosition = expression.IndexOfAny(new [] {'.', '['});
if (statementEndPosition == -1) return expression;
return expression.Substring(0, statementEndPosition);
}
private static string ClearIndexerStatement(string expression)
{
var statementEndPosition = expression.IndexOf(']');
if (statementEndPosition == expression.Length - 1) return "";
if (expression[statementEndPosition + 1] == '.') statementEndPosition++;
return expression.Substring(statementEndPosition + 1);
}
private static string GetIndex(string expression)
{
var closeBracketPosition = expression.IndexOf(']');
return expression.Substring(1, closeBracketPosition - 1);
}
private static string GetTargetPropertyExpression(string sourceExpression, string targetProperty)
{
var memberAccessTokenPosition = sourceExpression.LastIndexOf('.');
if (memberAccessTokenPosition == -1) // expression is just a property name
return targetProperty;
var newExpression = sourceExpression.Substring(0, memberAccessTokenPosition + 1) + targetProperty;
return newExpression;
}
}