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Route Constraints in Asp.net Core

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Route Constraints in Asp.net Core
Route constraints are an essential tool in ASP.NET Core routing that allows you to add extra validation to your route parameters. They define rules that restrict the values a parameter can accept, helping you filter out invalid requests before they reach your endpoint handlers.

Common Route Constraints
ASP.NET Core provides a variety of built-in route constraints:
int: Requires the parameter value to be an integer.
bool: Requires the parameter value to be a boolean (true or false).
datetime: Requires the parameter value to be a valid date and time string.
decimal, double, float, long: Require the parameter value to be of the specified numeric type.
guid: Requires the parameter value to be a valid GUID (Globally Unique Identifier).
alpha: Requires the parameter value to consist only of alphabetic characters (a-z, A-Z).
regex: Requires the parameter value to match a regular expression pattern.
length: Requires the parameter value to have a specific length or within a specified range.
min, max, range: Require the parameter value to be greater than or equal to the minimum (min), less than or equal to the maximum (max), or within a specific range (range).
Code
// … (UseRouting and other middleware) …
 
app.UseEndpoints(endpoints =>
{
    // … (other endpoints) …
 
    // Alphabetic and Length Constraint
    endpoints.Map(“employee/profile/{EmployeeName:length(4,7):alpha=harsha}”, async context =>
    {
        // …
    });
 
 
    // Integer, Range, and Optional Constraint
    endpoints.Map(“products/details/{id:int:range(1,1000)?}”, async context => {
        // …
    });
 
    // DateTime Constraint
    endpoints.Map(“daily-digest-report/{reportdate:datetime}”, async context =>
    {
        // …
    });
 
    // GUID Constraint
    endpoints.Map(“cities/{cityid:guid}”, async context =>
    {
        // …
    });
 
    // Int, Min, Regex Constraint
    endpoints.Map(“sales-report/{year:int:min(1900)}/{month:regex(^(apr|jul|oct|jan)$)}”, async context =>
    {
        // …
    });
});
 
// … (Fallback middleware) …
 
Alphabetic and Length Constraint: /employee/profile/{EmployeeName:length(4,7):alpha=harsha}: Ensures EmployeeName is 4-7 characters long and consists only of alphabetic characters. If not supplied, it defaults to “harsha”.
Integer, Range, and Optional Constraint: /products/details/{id:int:range(1,1000)?}: Requires id to be an integer between 1 and 1000. The question mark makes it optional.
DateTime Constraint: /daily-digest-report/{reportdate:datetime}: Requires reportdate to be a valid date-time string.
GUID Constraint: /cities/{cityid:guid}: Requires cityid to be a valid GUID.
Integer, Min, and Regex Constraint: /sales-report/{year:int:min(1900)}/{month:regex(^(apr|jul|oct|jan)$)}: Requires year to be an integer greater than or equal to 1900, and month to be one of the specified values (apr, jul, oct, jan).

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