How to read values from the querystring with ASP NET Core

Question

I m building one RESTful API using ASP NET Core MVC and I want to use querystring parameters to specify filtering and paging on a resource that returns a collection   In that case  I need to read the values passed in the querystring to filter and select the results to return    I ve already found out that inside the controller Get action accessing HttpContext Request Query returns one IQueryCollection   The problem is that I don t know how it is used to retrieve the values  In truth  I thought the way to do was by using  for example  string page   HttpContext Request Query  page     The problem is that HttpContext Request Query  page   doesn t return a string  but a StringValues   Anyway  how does one use the IQueryCollection to actually read the querystring values

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Startup cs add this service services AddSingleton lt IHttpContextAccessor  HttpContextAccessor gt     Your view add inject  inject Microsoft AspNetCore Http IHttpContextAccessor HttpContextAccessor get your value  Code  inject Microsoft AspNetCore Http IHttpContextAccessor HttpContextAccessor        var id   HttpContextAccessor HttpContext Request RouteValues  quot id quot         if  id    null                   parameter exist in your URL             string navigation   await Navigation WebNavigation activeTab

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You could use the ToString method on IQueryCollection which will return the desired value if a single page parameter is specified   string page   HttpContext Request Query  page   ToString      if there are multiple values like  page 1 amp page 2 then the result of the ToString call will be 1 2  But as  mike-g suggested in his answer you would better use model binding and not directly accessing the HttpContext Request Query object

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Some of the comments mention this as well  but asp net core does all this work for you    If you have a query string that matches the name it will be available in the controller    https   myapi some-endpoint 123 someQueryString YayThisWorks   HttpPost   Route  some-endpoint  someValue     public IActionResult SomeEndpointMethod int someValue  string someQueryString                Debug WriteLine someValue           Debug WriteLine someQueryString           return Ok            Ouputs    123  YayThisWorks

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I have a better solution for this problem    request is a member of abstract class ControllerBase  GetSearchParams   is an extension method created in bellow helper class    var searchparams   await Request GetSearchParams      I have created a static class with few extension methods  public static class HttpRequestExtension     public static async Task lt SearchParams gt  GetSearchParams this HttpRequest request                        var parameters   await request TupledParameters                 try                               for  var i   0  i  lt  parameters Count  i                                          if  parameters i  Item1      count   amp  amp  parameters i  Item2     0                                                 parameters i    new Tuple lt string  string gt    summary    count                                                            var searchCommand   SearchParams FromUriParamList parameters                   return searchCommand                            catch  FormatException formatException                                throw new FhirException formatException Message  OperationOutcome IssueType Invalid  OperationOutcome IssueSeverity Fatal  HttpStatusCode BadRequest                              public static async Task lt List lt Tuple lt string  string gt  gt  gt  TupledParameters this HttpRequest request            var list   new List lt Tuple lt string  string gt  gt               var query   request Query          foreach  var pair in query                        list Add new Tuple lt string  string gt  pair Key  pair Value                       if   request HasFormContentType                        return list                    var getContent   await request ReadFormAsync             if  getContent    null                        return list                    foreach  var key in getContent Keys                        if   getContent TryGetValue key  out StringValues values                                 continue                            foreach  var value in values                                list Add new Tuple lt string  string gt  key  value                                    return list            in this way you can easily access all your search parameters  I hope this will help many developers

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Maybe it helps  For get query string parameter in view View   inject Microsoft AspNetCore Http IHttpContextAccessor HttpContextAccessor    Context Request Query  quot uid quot     Startup cs ConfigureServices   services TryAddSingleton lt IHttpContextAccessor  HttpContextAccessor gt

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You can use  FromQuery  to bind a particular model to the querystring   https   docs microsoft com en-us aspnet core mvc models model-binding  e g    HttpGet    public IActionResult Get  FromQuery Name    page    string page

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IQueryCollection has a TryGetValue   on it that returns a value with the given key  So  if you had a query parameter called someInt  you could use it like so   var queryString   httpContext Request Query  StringValues someInt  queryString TryGetValue  someInt   out someInt   var daRealInt   int Parse someInt     Notice that unless you have multiple parameters of the same name  the StringValues type is not an issue

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ASP NET Core will automatically bind form values  route values and query strings by name   This means you can simply do this   HttpGet    public IActionResult Get int page             MVC will try to bind request data to the action parameters by name     below is a list of the data sources in the order that model binding looks through them  Form values  These are form values that go in the HTTP request using the POST method   including jQuery POST requests    Route values  The set of route values provided by Routing  Query strings  The query string part of the URI     Source  Model Binding in ASP NET Core  FYI  you can also combine the automatic and explicit approaches   HttpGet    public IActionResult Get int page         FromQuery Name    quot page-size quot    int pageSize

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Here is a code sample I ve used  with a  NET Core view           Microsoft Extensions Primitives StringValues queryVal       if  Context Request Query TryGetValue  yourKey   out queryVal   amp  amp          queryVal FirstOrDefault       yourValue

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You can just create an object like this   public class SomeQuery       public string SomeParameter   get  set        public int  SomeParameter2   get  set        And then in controller just make something like that    HttpGet  public IActionResult FindSomething  FromQuery  SomeQuery query           Your implementation goes here       Even better  you can create API model from    HttpGet  public IActionResult GetSomething  FromRoute  int someId   FromQuery  SomeQuery query    to    HttpGet  public IActionResult GetSomething ApiModel model   public class ApiModel        FromRoute      public int SomeId   get  set         FromQuery      public string SomeParameter   get  set         FromQuery      public int  SomeParameter2   get  set

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StringValues is an array of strings  You can get your string value by providing an index  e g  HttpContext Request Query  page   0

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in  net core if you want to access querystring in our view use it like    Context Request Query  yourKey     if we are in location where  Context is not avilable we can inject it like    inject Microsoft AspNetCore Http IHttpContextAccessor HttpContextAccessor  if  HttpContextAccessor HttpContext Request Query Keys Contains  yourKey             lt text gt do something  lt  text gt      also for cookies   HttpContextAccessor HttpContext Request Cookies  DeniedActions

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