Route parameters

Consider the following example: We want a page that can create a new customer, or display its details, and allow to modify them.

In the first case, the URL is admin/customer. There is no customer ID, because we are creating a new one.

In the second case, the URL contains the ID of the customer we want to edit, e.g. admin/customer/3.

Parameter with default value

We can cover both cases using a single route. Its registration will look like this:

config.RouteTable.Add("AdminCustomer", "admin/customer/{Id}", "Views/admin/customer.dothtml", new { Id = 0 });

Notice that the route contains the parameter {Id}. Also, the fourth argument says that if the parameter is not present, its value should be 0.

In the viewmodel, we can instruct DotVVM to inject the parameter value into a property by using FromRoute attribute.

 [FromRoute("Id")]
 public int CustomerId { get; set; }

There is also a FromQuery attribute which can bind the property using the value from the URL query string (e. g. admin/customers?page=2).

Alternatively, you can read the value of the route parameter using the following code:

var customerId = Convert.ToInt32(Context.Parameters["Id"]);
if (customerId == 0) 
{
    // new customer
} 
else 
{
    // existing customer
}

Make sure you convert the parameter to the correct type using Convert.To* method. If the parameter is optional, use TryGetValue or ContainsKey before reading the parameter, otherwise you'll get an exception.

Optional parameters

We can also make the parameter optional (without the default value):

config.RouteTable.Add("AdminCustomer", "admin/customer/{Id?}", "Views/admin/customer.dothtml");

In that case, you need to check whether the parameter is present in the URL:

if (!Context.Parameters.ContainsKey("Id")) 
{
    // new customer
}
else 
{
    // existing customer
    var customerId = Convert.ToInt32(Context.Parameters["Id"]);
}

Route constraints

Additionally, you can use the route parameter constraints:

config.RouteTable.Add("AdminCustomer", "admin/customer/{Id:int}", "Views/admin/customer.dothtml", new { Id = 0 });

Notice the {Id:int} parameter, which says that the route will be matched only if the Id is an integer value.

DotVVM supports the following route constraints:

• alpha - alphabetic characters
• bool - true / false value
• decimal - decimal values with . decimal point symbol
• double - double values with . decimal point symbol
• float - float values with . decimal point symbol
• guid - a Guid value
• int - any integer number
• posint- a positive integer number (or zero)
• length(x) - any value with length of x characters
• long - any long integer number
• max(x) - any double value with . decimal point symbol that is less than x
• min(x) - any double value with . decimal point symbol that is greater than x
• range(x, y) - any double value with . decimal point symbol that is between x and y
• maxlength(x) - any value with length of x characters or less
• minlength(x) - any value with length of x characters or more
• regex(x) - any value that matches the regular expression x

Every parameter can specify only one constraint.

Custom constraints

You can also define your own route constraints by creating a class that implements the IRouteParameterConstraint interface.

These custom constraints can be registered using this syntax in the DotvvmStartup file:

config.RouteConstraints.Add("customConstraint", new MyRouteConstraint());

See also

• Route redirection
• Auto-discover routes
• Custom presenter