Custom Attribute Routing in ASP.NET MVC 5


A previous blog post discussed how to enable and use the basics of attribute routing within an MVC application. The blog also touched upon URI parameter constraints and the out-of-the-box constraints with MVC 5.

The general syntax for imposing constraint is {parameter:constraint}

Below is a list of constraints with examples:

Constraint Description Example
alpha Matches uppercase or lowercase Latin alphabet characters (a-z, A-Z) {x:alpha}
bool Matches a Boolean value. {x:bool}
datetime Matches a DateTime value. {x:datetime}
decimal Matches a decimal value. {x:decimal}
double Matches a 64-bit floating-point value. {x:double}
float Matches a 32-bit floating-point value. {x:float}
guid Matches a GUID value. {x:guid}
int Matches a 32-bit integer value. {x:int}
length Matches a string with the specified length or within a specified range of lengths. {x:length(6)}
long Matches a 64-bit integer value. {x:long}
max Matches an integer with a maximum value. {x:max(10)}
maxlength Matches a string with a maximum length. {x:maxlength(10)}
min Matches an integer with a minimum value. {x:min(10)}
minlength Matches a string with a minimum length. {x:minlength(10)}
range Matches an integer within a range of values. {x:range(10,50)}
regex Matches a regular expression. {x:regex(^\d{3}-\d{3}-\d{4}$)}

How to create your own custom parameter constraint:

Values Constraint

This constraint will be used to validate a string parameter by allowing the developer to specify the allowed values passed by the parameter. You’re probably thinking why not handle validating the parameter in the controller action or mode… But if you know the static values that can be passed, why clutter up your controller or model?

First we need to create a ValuesConstraint class that will implement the IRouteConstraint interface. This interface only contains one method.

Sample Code 2

Once we have the class, we need to add an array variable for our valid parameter values and a constructor to populate variable. In the match method, we get the parameter value and validate it against the allowed values. You can set it up to be case-sensitive, however, in the example below, we’re ignoring case.

Sample Code 3

And that’s how to create a custom constraint, folks. Now we can add this to our controller action.

Sample Code 4

The syntax for imposing this constraint is {parameter:values(string[])}


Creating your own custom constraints can be very quick and easy. This a basic example, but can be easily modified to meet your needs and complexities.



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