web-api POST body object always null

Question

I m still learning web API  so pardon me if my question sounds stupid   I have this in my StudentController   public HttpResponseMessage PostStudent  FromBody Models Student student        if  DBManager createStudent student     null          return Request CreateResponse HttpStatusCode Created  student       else         return Request CreateResponse HttpStatusCode BadRequest  student       In order to test if this is working  I m using Google Chrome s extension  Postman  to construct the HTTP POST request to test it out   This is my raw POST request   POST  api Student HTTP 1 1 Host  localhost 1118 Content-Type  application json Cache-Control  no-cache    student      name   John Doe    age  18   country   United States of America       student is supposed to be an object  but when I debug the application  the API receives the student object but the content is always null

User · Answer

In my case  using postman I was sending a DateTime with invalid separators     so the parse failed silently   Be sure you are passing valid params to your class constructor

User · Answer

I was looking for a solution to my problem for some minutes now  so I ll share my solution    When you have a custom constructor within your model  your model also needs to have an empty default constructor  Otherwise the model can t be created  obviously   Be careful while refactoring

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In my case   NET Core 3 0  I had to configure JSON serialization to resolve camelCase properties using AddNewtonsoftJson     services AddMvc options   gt            Irrelevant for the answer      AddNewtonsoftJson options   gt        options SerializerSettings ContractResolver   new CamelCasePropertyNamesContractResolver          Do this in your Startup   Dependency Injection setup

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If the any of values of the request s JSON object are not the same type as expected by the service then the  FromBody  argument will be null   For example  if the age property in the json had a float value       age  18 0   but the API service expects it to be an int      age  18   then student will be null   No error messages will be sent in the response unless no null reference check

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I had the same problem    In my case  the problem was in public int  CreditLimitBasedOn   get  set    property I had    my JSON had the value  CreditLimitBasedOn  true when It should contain an integer  This property prevented the whole object being deserialized on my api method

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This is another issue related to invalid property values in an Angular Typescript request   This is was related to the conversion between a Typescript number to an int Int32  in C   I was using Ticks  UTC milliseconds  which is larger than the signed  Int32 range  int in C    Changed the C  model from int to long and everything worked fine

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If this is because Web API 2 ran into a deserialization problem due to mismatched data types  it s possible to find out where it failed by inspecting the content stream  It will read up until it hits an error  so if you read the content as a string  you should have the back half of the data you posted   string json   await Request Content ReadAsStringAsync      Fix that parameter  and it should make it further next time  or succeed if you re lucky

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Just to add my history to this thread  My model   public class UserProfileResource       public Guid Id   get  set        public string FirstName   get  set        public string LastName   get  set        public string Phone   get  set         public UserProfileResource                   The above object couldn t be serialized in my API Controller and would always return null  The issue was with Id of type Guid  everytime I passed empty string as an Id  being naive that it will automatically be converted to Guid Empty  from my frontend I received null object as  FromBody  paramether    Solution was either to    pass valid Guid value  or change Guid to String

User · Answer

Seems like there can be many different causes of this problem     I found that adding an OnDeserialized callback to the model class caused the parameter to always be null  Exact reason unknown   using System Runtime Serialization      Validate request  OnDeserialized      TODO  Causes parameter to be null public void DoAdditionalValidatation

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I ve hit this problem so many times  but actually  it s quite straightforward to track down the cause   Here s today s example   I was calling my POST service with an AccountRequest object  but when I put a breakpoint at the start of this function  the parameter value was always null   But why      ProducesResponseType typeof DocumentInfo     201    HttpPost  public async Task lt IActionResult gt  Post  FromBody  AccountRequest accountRequest            At this point     accountRequest is null    but why                 other code          To identify the problem  change the parameter type to string  add a line to get JSON Net to deserialize the object into the type you were expecting  and put a breakpoint on this line    ProducesResponseType typeof DocumentInfo     201    HttpPost  public async Task lt IActionResult gt  Post  FromBody  string ar            Put a breakpoint on the following line    what is the value of  ar        AccountRequest accountRequest   JsonConvert DeserializeObject lt AccountRequest gt  ar                other code         Now  when you try this  if the parameter is still blank or null  then you simply aren t calling the service properly   However  if the string does contain a value  then the DeserializeObject should point you towards the cause of the problem  and should also fail to convert your string into your desired format   But with the raw  string  data which it s trying to deserialize  you should now be able to see what s wrong with your parameter value    In my case  we were calling the service with an AccountRequest object which had been accidentally serialized twice

User · Answer

After Three days of searching and none of above solutions worked for me   I found another approach to this problem in this Link  HttpRequestMessage  I used one of the solutions in this site    HttpPost  public async System Threading Tasks Task lt string gt  Post HttpRequestMessage request        string body   await request Content ReadAsStringAsync        return body

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Maybe for someone it will be helpful  check the access modifiers for your DTO Model class  properties  they should be public  In my case during refactoring domain object internals were moved to DTO like this      Domain object public class MyDomainObject       public string Name   get  internal set        public string Info   get  internal set         DTO public class MyDomainObjectDto       public Name   get  internal set        lt -- The problem is in setter access modifier  and carelessly performed refactoring       public string Info   get  internal set        DTO is being finely passed to client  but when the time comes to pass the object back to the server it had only empty fields  null default value   Removing  internal  puts things in order  allowing deserialization mechanizm to write object s properties   public class MyDomainObjectDto       public Name   get  set        public string Info   get  set

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I just ran into this and was frustrating  My setup  The header was set to Content-Type  application JSON and was passing the info from the body with JSON format  and was reading  FromBody  on the controller  Everything was set up fine and I expect it to work  but the problem was with the JSON sent over  Since it was a complex structure  one of my classes which was defined  Abstract  was not getting initialized and hence the values weren t assigned to the model properly  I removed the abstract keyword and it just worked      One tip  the way I could figure this out was to send data in parts to my controller and check when it becomes null    since it was a complex model I was appending one model at a time to my request params  Hope it helps someone who runs into this stupid issue

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I had this problem in my  NET Framework Web API  because my model existed in a  NET Standard project that referenced a different version of data annotations   Adding the ReadAsAsync line below highlighted the cause for me   public async Task lt HttpResponseMessage gt  Register RegistrationDetails registrationDetails        var regDetails   await Request Content ReadAsAsync lt RegistrationDetails gt

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In my case the problem was the DateTime object I was sending  I created a DateTime with  yyyy-MM-dd   and the DateTime that was required by the object I was mapping to needed  HH-mm-ss  aswell  So appending  00-00  solved the problem  the full item was null because of this

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I was also trying to use the  FromBody   however  I was trying to populate a string variable because the input will be changing and I just need to pass it along to a backend service but this was always null  Post  FromBody string Input      So I changed the method signature to use a dynamic class and then convert that to string  Post dynamic DynamicClass       string Input   JsonConvert SerializeObject DynamicClass     This works well

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FromBody is a strange attribute in that the input POST values need to be in a specific format for the parameter to be non-null  when it is not a primitive type   student here     Try your request with   name   John Doe    age  18   country   United States of America   as the json   Remove the  FromBody  attribute and try the solution  It should work for non-primitive types   student  With the  FromBody  attribute  the other option is to send the values in  Value format  rather than key value format  This would mean your key value of student should be an empty string       There are also other options to write a custom model binder for the student class and attribute the parameter with your custom binder

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I used HttpRequestMessage and my problem got solved after doing so much research   HttpPost  public HttpResponseMessage PostProcedure HttpRequestMessage req

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This is a little old one and my answer will go down to the last place but even so I would like to share my experience   Tried every suggestion but still having the same  null  value in a PUT  FromBody    Finally found it was all about Date format while JSON serializing the EndDate property of my Angular Object   No error was thrown  just received an empty FromBody object

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None of the above was my solution  in my case the issue is that  ApiController  was not added to the controller so it is giving Null value   Produces  application json     Route  api  controller      ApiController     This was my problem  make sure that it is there  public class OrderController   Controller

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I spend several hours with this issue       Getters and setters are REQUIRED in POST parameters object declaration  I do not recommend using simple data objects  string int       as they require special request format    HttpPost  public HttpResponseMessage PostProcedure EdiconLogFilter filter           Does not work when   public class EdiconLogFilter       public string fClientName      public string fUserName      public string fMinutes      public string fLogDate      Works fine when   public class EdiconLogFilter       public string fClientName   get  set        public string fUserName   get  set        public string fMinutes   get  set        public string fLogDate   get  set

User · Answer

Just one more thing to look at     my model was marked as  Serializable  and that was causing the failure

User · Answer

If using Postman  make sure that    You have set a  Content-Type  header to  application json  You are sending the body as  raw  You don t need to specify the parameter name anywhere if you are using  FromBody    I was stupidly trying to send my JSON as form data  duh

User · Answer

Check if JsonProperty attribute is set on the fields that come as null - it could be that they are mapped to different json property-names

User · Answer

TL DR  Don t use  FromBody   but roll your own version of it with better error handling  Reasons given below   Other answers describe many possible causes of this problem  However  the root cause is that  FromBody  simply has terrible error handling  which makes it almost useless in production code   For example  one of the most typical reasons for the parameter to be null is that the request body has invalid syntax  e g   invalid JSON   In this case  a reasonable API would return 400 BAD REQUEST  and a reasonable web framework would do this automatically  However  ASP NET Web API is not reasonable in this regard  It simply sets the parameter to null  and the request handler then needs  manual  code to check if the parameter is null   Many of the answers given here are therefore incomplete with regards to error handling  and a buggy or malicious client may cause unexpected behavior on the server side by sending an invalid request  which will  in the best case  throw a NullReferenceException somewhere and return an incorrect status of 500 INTERNAL SERVER ERROR or  worse  do something unexpected or crash or expose a security vulnerability   A proper solution would be to write a custom   FromBody   attribute which does proper error handling and returns proper status codes  ideally with some diagnostic information to aid client developers   A solution that might help  not tested yet  is to make parameters required  as follows  https   stackoverflow com a 19322688 2279059  The following clumsy solution also works      BAD EXAMPLE  but may work reasonably well for  internal  APIs     public HttpResponseMessage MyAction  FromBody  JObject json         Check if JSON from request body has been parsed correctly   if  json    null        var response   new HttpResponseMessage HttpStatusCode BadRequest          ReasonPhrase    Invalid JSON             throw new HttpResponseException response          MyParameterModel param    try       param   json ToObject lt MyParameterModel gt           catch  JsonException e        var response   new HttpResponseMessage HttpStatusCode BadRequest          ReasonPhrase   String Format  Invalid parameter   0    e Message             throw new HttpResponseException response                 Request handling goes here          This does  hopefully  proper error handling  but is less declarative  If  for example  you use Swagger to document your API  it will not know the parameter type  which means you need to find some manual workaround to document your parameters  This is just to illustrate what  FromBody  should be doing   EDIT  A less clumsy solution is to check ModelState  https   stackoverflow com a 38515689 2279059  EDIT  It appears that ModelState IsValid is not  as one would expect  set to false if using JsonProperty with Required   Required Always and a parameter is missing  So this is also useless   However  in my opinion  any solution that requires writing additional code in every request handler is unacceptable  In a language like  NET  with powerful serialization capabilities  and in a framework like ASP NET Web API  request validation should be automatic and built-in  and it is totally doable  even though Microsoft does not provide the necessary built-in tools

User · Answer

It can be helpful to add TRACING to the json serializer so you can see what s up when things go wrong   Define an ITraceWriter implementation to show their debug output like   class TraceWriter   Newtonsoft Json Serialization ITraceWriter       public TraceLevel LevelFilter           get               return TraceLevel Error                       public void Trace TraceLevel level  string message  Exception ex                Console WriteLine  JSON  0   1    2    level  message  ex             Then in your WebApiConfig do       config Formatters JsonFormatter SerializerSettings TraceWriter   new TraceWriter       maybe wrap it in an  if DEBUG

[c#] web-api POST body object always null

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