Why do we have to specify FromBody and FromUri

Question

Why are the FromBody and FromUri attributes needed in ASP NET Web API    What are the differences between using the attributes and not using them

User · Answer

When a parameter has  FromBody   Web API uses the Content-Type header to select a formatter  In this example  the content type is  quot application json quot  and the request body is a raw JSON string  not a JSON object   At most one parameter is allowed to read from the message body  So this will not work     Caution  Will not work      public HttpResponseMessage Post  FromBody  int id   FromBody  string name           The reason for this rule is that the request body might be stored in a non-buffered stream that can only be read once  Please go through the website for more details  https   docs microsoft com en-us aspnet web-api overview formats-and-model-binding parameter-binding-in-aspnet-web-api

User · Answer

Just addition to above answers      FromUri  can also be used to bind complex types from uri parameters instead of passing parameters from querystring  For Ex    public class GeoPoint       public double Latitude   get  set         public double Longitude   get  set        RoutePrefix  api Values    public ValuesController   ApiController        Route   Latitude   Longitude         public HttpResponseMessage Get  FromUri  GeoPoint location              Can be called like   http   localhost api values 47 678558 -122 130989

User · Answer

The default behavior is    If the parameter is a primitive type  int  bool  double        Web API tries to get the value from the URI of the HTTP request  For complex types  your own object  for example  Person   Web API tries to read the value from the body of the HTTP request    So  if you have    a primitive type in the URI  or a complex type in the body      then you don t have to add any attributes  neither  FromBody  nor  FromUri     But  if you have a primitive type in the body  then you have to add  FromBody  in front of your primitive type parameter in your WebAPI controller method   Because  by default  WebAPI is looking for primitive types in the URI of the HTTP request    Or  if you have a complex type in your URI  then you must add  FromUri    Because  by default  WebAPI is looking for complex types in the body of the HTTP request by default    Primitive types   public class UsersController   ApiController          api users     public HttpResponseMessage Post  FromBody int id                      api users id     public HttpResponseMessage Post int id                          Complex types   public class UsersController   ApiController                 api users     public HttpResponseMessage Post User user                       api users user     public HttpResponseMessage Post  FromUri User user                          This works as long as you send only one parameter in your HTTP request  When sending multiple  you need to create a custom model which has all your parameters like this   public class MyModel       public string MyProperty   get  set        public string MyProperty2   get  set        Route  search     HttpPost  public async Task lt dynamic gt  Search  FromBody  MyModel model           model MyProperty         model MyProperty2      From Microsoft s documentation for parameter binding in ASP NET Web API      When a parameter has  FromBody   Web API uses the Content-Type header   to select a formatter  In this example  the content type is    application json  and the request body is a raw JSON string  not a   JSON object   At most one parameter is allowed to read from the   message body        This should work   public HttpResponseMessage Post  FromBody  string name                This will not work      Caution  This won t work      public HttpResponseMessage Post  FromBody  int id   FromBody  string name                The reason for this rule is that the request body might be stored in a   non-buffered stream that can only be read once

User · Answer

When the ASP NET Web API calls a method on a controller  it must set values for the parameters  a process called parameter binding   By default  Web API uses the following rules to bind parameters    If the parameter is a  simple  type  Web API tries to get the value from the URI  Simple types include the  NET primitive types  int  bool  double  and so forth   plus TimeSpan  DateTime  Guid  decimal  and string  plus any type with a type converter that can convert from a string  For complex types  Web API tries to read the value from the message body  using a media-type formatter    So  if you want to override the above default behaviour and force Web API to read a complex type from the URI  add the  FromUri  attribute to the parameter  To force Web API to read a simple type from the request body  add the  FromBody  attribute to the parameter   So  to answer your question  the need of the  FromBody  and  FromUri  attributes in Web API is simply to override  if necessary  the default behaviour as described above  Note that you can use both attributes for a controller method  but only for different parameters  as demonstrated here   There is a lot more information on the web if you google  web api parameter binding

[asp.net-web-api] Why do we have to specify FromBody and FromUri?

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