ASP.NET WebAPI 2：处理空字符串查询参数

Question

We have an api used to get data of products:

public IHttpActionResult GetProducts(ProductFilter productFilter)
{
    try
    {
        .....
    }
    catch(Exception)
    {
        throw new OurCustomException();
    }
}

and

public class ProductFilter
{
    [RegularExpression(@"^[a-zA-Z0-9]{11}$")]
    public String Number { get; set; }
    .....
}

Here is what i want:

1. When send GET /api/products?number=Test1234567 it will return information of a product with the number "Test1234567"

2. When send GET /api/products?number= it will return error because the empty string does not match the regex

3. When send GET /api/products it will return information of all products

So can you suggest me any way to do this by using just Validation Attribute, since we have a common method to handle ValidationException and we cannot throw ValidationException from method GetProducts . I have tried to use [Required] and [DisplayFormat(ConvertEmptyStringToNull = false)] on Number but none of them worked.

And please also inform me if it is impossible.

Answer 1

EDIT: I think your problem is that you are not passing full model as parameter - your are getting null once binder tries to bind query string. This is not a problem with your regex. To get it working you should make q request like GET /api/products?number=&prop1=some_value&prop2=some_value

---

Original answer:

I think changing your regex to:

public class ProductFilter
{
    [RegularExpression(@"^(|[a-zA-Z0-9]{11})$")]
    public String Number { get; set; }
    .....
}

should do a trick.

However MSDN documentation states that:

If the value of the property is null or an empty string (""), the value automatically passes validation for the RegularExpressionAttribute attribute.

So it should work anyway. Additionally we can check RegularExpression code:

    public override bool IsValid(object value)
    {
      this.SetupRegex();
      string input = Convert.ToString(value, (IFormatProvider) CultureInfo.CurrentCulture);
      if (string.IsNullOrEmpty(input))
        return true;
      Match match = this.Regex.Match(input);
      if (match.Success && match.Index == 0)
        return match.Length == input.Length;
      return false;
    }

as you can see, it allows null or empty input so your problem is rather different.