Separate error message for Minimum and Maximum string length – MVC4 Data annotation

The LINQ2SQL code generator places an attribute on property fields similar to:

[Column(Storage="_Message", DbType="NVarChar(20)")]

It would be simple to extract and use this information at runtime:

public class Row
{
    // normally generated by LINQ2SQL
    [Column(Storage = "_Message", DbType = "NVarChar(20)")]
    public string Message
    {
        get;
        set;
    }

    // normally generated by LINQ2SQL
    [Column(Storage = "_Property", DbType = "NVarChar(20) NOT NULL")]
    public string Property
    {
        get;
        set;
    }
}

public class VarCharInfo
{
    public int? MaxLen;
    public bool IsNullable;
}

public static VarCharInfo GetVarCharInfo(PropertyInfo propertyInfo)
{
    var attrib = propertyInfo.GetCustomAttributes(typeof(ColumnAttribute), false)
        .OfType<ColumnAttribute>()
        .FirstOrDefault();

    if (attrib == null || attrib.DbType == null)
    {
        return null;
    }

    var match = Regex.Match(attrib.DbType, @"VarChar\((?'len'\d+)\)(?'notnull' NOT NULL)?");

    if (!match.Success)
    {
        return null;
    }

    var rvl = new VarCharInfo();

    rvl.MaxLen = int.Parse(match.Groups["len"].Captures[0].Value);
    rvl.IsNullable = match.Groups["notnull"].Success;

    return rvl;
}

public static bool ValidateVarCharColumns(object dataObject)
{
    bool success = true;

    foreach (var propertyInfo in dataObject.GetType()
        .GetProperties()
        .Where(pi => pi.PropertyType == typeof(string)))
    {
        var vci = GetVarCharInfo(propertyInfo);

        if (vci != null)
        {
            var currentValue = propertyInfo.GetGetMethod()
                .Invoke(dataObject, null) as string;

            if (currentValue == null)
            {
                if (!vci.IsNullable)
                {
                    // more work: value is null but it shouldn't be
                    success = false;
                }
            }
            else if (vci.MaxLen != null && currentValue.Length > vci.MaxLen)
            {
                // more work: value is longer than db allows
                success = false;
            }
        }
    }

    return success;
}

static void UsageTest()
{
    Row t = new Row();
    t.Message = "this message is longer than 20 characters";
    // t.Property is null

    ValidateVarCharColumns(t);  // returns false!
}

You could use the ValidationParameters property to add custom parameters to the rule:

public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
{
    var rule = new ModelClientValidationRule
    {
        ErrorMessage = this.ErrorMessage,
        ValidationType = "futuredate",
    };
    rule.ValidationParameters.Add("param1", "value1");
    rule.ValidationParameters.Add("param2", "value2");
    yield return rule;
}

which could be used in the adapter:

jQuery.validator.unobtrusive.adapters.add(
    'futuredate', 
    [ 'param1', 'param2' ],
    function (options) {
        var param1 = options.params.param1; // shall equal 'value1'
        var param2 = options.params.param2; // shall equal 'value2'
        // TODO: use those custom parameters to define the client rules
    }
);

UPDATE:

As requested in the comments section here's how you could pass those parameters to the custom validator rule function:

jQuery.validator.unobtrusive.adapters.add(
    'futuredate', 
    [ 'param1', 'param2' ],
    function (options) {
        // simply pass the options.params here
        options.rules['greaterThan'] = options.params;
        options.messages['greaterThan'] = options.message;
    }
);

jQuery.validator.addMethod('greaterThan', function (value, element, params) {
    // params here will equal { param1: 'value1', param2: 'value2' }
    return ...
}, '');