c# - json serializer NullValueHandling without use datamember attribute -

in web api project, right i'm skipping null values. therefore, return json ignores null values , prints property.

in global.asax file:

//manage null in response var json = globalconfiguration.configuration.formatters.jsonformatter; json.serializersettings.nullvaluehandling = newtonsoft.json.nullvaluehandling.ignore; 

however, want replace null values "-". but, dont want use data member attribute each property...

[defaultvalue("-")].  

i have more 10 classes in project... so, not elegant solution.

i wish simple solution , apply conversion, null values global.asax

example.

public class user {     public string user { get; set; }      public string name { get; set; }      public string dni { get; set; } } 

when exists data, service return

{   "user": "usertest",   "name": "nametest",   "dni": "123456789" } 

but, when dni, doesn't exists, respond this

{   "user": "usertest",   "name": "nametest",   "dni": "" } 

so, respond follows

{   "user": "usertest",   "name": "nametest",   "dni": "-" } 

i don't recommend doing this. problem if 1 if string-value properties happens have same value "null value" "-", lose information when serializing, namely whether or not property null.

that being said, can contractresolver overriding jsonproperty.valueprovider string-valued properties:

public class stringremappingcontractresolver : defaultcontractresolver {     static readonly object nullvalue;      static stringremappingcontractresolver() { nullvalue = new object(); }      readonly dictionary<object, object> map;     readonly ilookup<object, object> reversemap;      public stringremappingcontractresolver() : this(new keyvaluepair<object, object> [] { new keyvaluepair<object, object>(null, "-")})      {     }      public stringremappingcontractresolver(ienumerable<keyvaluepair<object, object>> map)     {         if (map == null)             throw new argumentnullexception("map");         this.map = map.todictionary(p => p.key ?? nullvalue, p => p.value);         this.reversemap = map.tolookup(p => p.value ?? nullvalue, p => p.key);     }      class stringremappingvalueprovider : ivalueprovider     {         readonly ivalueprovider baseprovider;         readonly dictionary<object, object> map;         readonly ilookup<object, object> reversemap;          public stringremappingvalueprovider(ivalueprovider baseprovider, dictionary<object, object> map, ilookup<object, object> reversemap)         {             if (baseprovider == null)                 throw new argumentnullexception("baseprovider");             this.baseprovider = baseprovider;             this.map = map;             this.reversemap = reversemap;         }          #region ivalueprovider members          public object getvalue(object target)         {             var value = baseprovider.getvalue(target);             object mapped;             if (map.trygetvalue(value ?? nullvalue, out mapped))                 value = mapped;             return value;         }          public void setvalue(object target, object value)         {             foreach (var mapped in reversemap[value ?? nullvalue])             {                 // use first.                 value = mapped;                 break;             }             baseprovider.setvalue(target, value);         }          #endregion     }      protected override jsonproperty createproperty(memberinfo member, memberserialization memberserialization)     {         var property = base.createproperty(member, memberserialization);         if (property.propertytype == typeof(string))         {             property.valueprovider = new stringremappingvalueprovider(property.valueprovider, map, reversemap);         }         return property;     } } 

then use like:

public class user {     public string user { get; set; }      public string name { get; set; }      public string dni { get; set; } }  public class testclass {     public static void test()     {         var settings = new jsonserializersettings { contractresolver = new stringremappingcontractresolver() };          var user = new user { user = "usertest", name = "nametest", dni = null };         var json = jsonconvert.serializeobject(user, settings);         debug.writeline(json); // prints {"user":"usertest","name":"nametest","dni":"-"}         debug.assert(jtoken.deepequals(jtoken.parse(json), jtoken.parse(@"{'user':'usertest','name':'nametest','dni':'-'}"))); // no assert         var userback = jsonconvert.deserializeobject<user>(json, settings);         debug.assert(user.dni == userback.dni && user.name == userback.name && user.user == userback.user); // no assert     } }