How to ignore a property in class if null using json net

Question

I am using Json NET to serialize a class to JSON   I have the class like this   class Test1        JsonProperty  id        public string ID   get  set         JsonProperty  label        public string Label   get  set         JsonProperty  url        public string URL   get  set         JsonProperty  item        public List lt Test2 gt  Test2List   get  set        I want to add a JsonIgnore   attribute to Test2List property only when Test2List is null  If it is not null then I want to include it in my json

User · Answer

You can do this to ignore all nulls in an object you re serializing  and any null properties won t then appear in the JSON  JsonSerializerSettings settings   new JsonSerializerSettings    settings NullValueHandling   NullValueHandling Ignore  var myJson   JsonConvert SerializeObject myObject  settings

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To expound slightly on GlennG s very helpful answer  translating the syntax from C  to VB Net is not always  obvious   you can also decorate individual class properties to manage how null values are handled  If you do this don t use the global JsonSerializerSettings from GlennG s suggestion  otherwise it will override the individual decorations  This comes in handy if you want a null item to appear in the JSON so the consumer doesn t have to do any special handling   If  for example  the consumer needs to know an array of optional items is normally available  but is currently empty    The decoration in the property declaration looks like this    lt JsonPropertyAttribute  MyProperty   DefaultValueHandling  NullValueHandling Include  gt  Public Property MyProperty As New List of String    For those properties you don t want to have appear at all in the JSON change   NullValueHandling Include to   NullValueHandling Ignore  By the way - I ve found that you can decorate a property for both XML and JSON serialization just fine  just put them right next to each other   This gives me the option to call the XML serializer in dotnet or the NewtonSoft serializer at will - both work side-by-side and my customers have the option to work with XML or JSON   This is slick as snot on a doorknob since I have customers that require both

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As can be seen in this link on their site  http   james newtonking com archive 2009 10 23 efficient-json-with-json-net-reducing-serialized-json-size aspx  I support using  Default    to specify default values  Taken from the link     public class Invoice     public string Company   get  set      public decimal Amount   get  set          false is default value of bool   public bool Paid   get  set         null is default value of nullable   public DateTime  PaidDate   get  set          customize default values    DefaultValue 30     public int FollowUpDays   get  set       DefaultValue        public string FollowUpEmailAddress   get  set        Invoice invoice   new Invoice     Company    Acme Ltd      Amount   50 0m    Paid   false    FollowUpDays   30    FollowUpEmailAddress   string Empty    PaidDate   null     string included   JsonConvert SerializeObject invoice    Formatting Indented    new JsonSerializerSettings                   Company    Acme Ltd          Amount   50 0        Paid   false        PaidDate   null        FollowUpDays   30        FollowUpEmailAddress            string ignored   JsonConvert SerializeObject invoice    Formatting Indented    new JsonSerializerSettings   DefaultValueHandling   DefaultValueHandling Ignore                 Company    Acme Ltd          Amount   50 0

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Similar to  sirthomas s answer  JSON NET also respects the EmitDefaultValue property on DataMemberAttribute    DataMember Name  property name   EmitDefaultValue false     This may be desirable if you are already using  DataContract  and  DataMember  in your model type and don t want to add JSON NET-specific attributes

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This does not exactly answer the original question  but may prove useful depending on the use case   And since I wound up here after my search  it may be useful for others   In my most recent experience  I m working with a PATCH api  If a property is specified but with no value given  null undefined because it s js   then the property and value are removed from the object being patched  So I was looking for a way to selectively build an object that could be serialized in such a way that this would work  I remembered seeing the ExpandoObject  but never had a true use case for it until today  This allows you to build an object dynamically  so you won t have null properties unless you want them there  Here is a working fiddle  with the code below  Results  Standard class serialization     noName    quot Name quot  null  quot Company quot   quot Acme quot       noCompany    quot Name quot   quot Fred Foo quot   quot Company quot  null      defaultEmpty    quot Name quot  null  quot Company quot  null  ExpandoObject serialization     noName    quot Company quot   quot Acme quot       noCompany    quot name quot   quot Fred Foo quot       defaultEmpty      Code  using Newtonsoft Json  using System  using System Dynamic                       public class Program       public static void Main                 SampleObject noName   new SampleObject     Company    quot Acme quot             SampleObject noCompany   new SampleObject     Name    quot Fred Foo quot             SampleObject defaultEmpty   new SampleObject                              Console WriteLine  quot Standard class serialization quot            Console WriteLine   quot     noName    JsonConvert SerializeObject noName    quot            Console WriteLine   quot     noCompany    JsonConvert SerializeObject noCompany    quot            Console WriteLine   quot     defaultEmpty    JsonConvert SerializeObject defaultEmpty    quot                              Console WriteLine  quot ExpandoObject serialization quot            Console WriteLine   quot     noName    JsonConvert SerializeObject noName CreateDynamicForPatch      quot            Console WriteLine   quot     noCompany    JsonConvert SerializeObject noCompany CreateDynamicForPatch      quot            Console WriteLine   quot     defaultEmpty    JsonConvert SerializeObject defaultEmpty CreateDynamicForPatch      quot             public class SampleObject       public string Name   get  set        public string Company   get  set             public object CreateDynamicForPatch                 dynamic x   new ExpandoObject                     if   string IsNullOrWhiteSpace Name                         x name   Name                             if   string IsNullOrEmpty Company                         x Company   Company                             return x

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As per James Newton King  If you create the serializer yourself rather than using JavaScriptConvert there is a NullValueHandling property which you can set to ignore   Here s a sample   JsonSerializer  jsonWriter   new JsonSerializer                                    NullValueHandling   NullValueHandling Ignore                                     Alternatively  as suggested by  amit  JsonConvert SerializeObject myObject                               Newtonsoft Json Formatting None                               new JsonSerializerSettings                                    NullValueHandling   NullValueHandling Ignore

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You can write   JsonProperty  property name  DefaultValueHandling   DefaultValueHandling Ignore    It also takes care of not serializing properties with default values  not only null   It can be useful for enums for example

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In  Net Core this is much easier now  In your startup cs just add json options and you can configure the settings there    public void ConfigureServices IServiceCollection services         services AddMvc   AddJsonOptions options   gt       options SerializerSettings NullValueHandling   NullValueHandling Ignore

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Here s an option that s similar  but provides another choice   public class DefaultJsonSerializer   JsonSerializerSettings       public DefaultJsonSerializer                 NullValueHandling   NullValueHandling Ignore            Then  I use it like this   JsonConvert SerializeObject postObj  new DefaultJsonSerializer       The difference here is that    Reduces repeated code by instantiating and configuring JsonSerializerSettings each place it s used  Saves time in configuring every property of every object to be serialized  Still gives other developers flexibility in serialization options  rather than having the property explicitly specified on a reusable object  My use-case is that the code is a 3rd party library and I don t want to force serialization options on developers who would want to reuse my classes  Potential drawbacks are that it s another object that other developers would need to know about  or if your application is small and this approach wouldn t matter for a single serialization

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With System Text Json and  NET Core 3 0 this worked for me   var jsonSerializerOptions   new JsonSerializerOptions         IgnoreNullValues   true    var myJson   JsonSerializer Serialize myObject  jsonSerializerOptions

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An adaption to  Mrchief s    amit s answer   but for people using VB   Dim JSONOut As String   JsonConvert SerializeObject             myContainerObject              New JsonSerializerSettings With                     NullValueHandling   NullValueHandling Ignore                        See    Object Initializers  Named and Anonymous Types  Visual Basic    https   msdn microsoft com en-us library bb385125 aspx

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With Json NET      public class Movie                public string Name   get  set                public string Description   get  set                public string Classification   get  set                public string Studio   get  set                public DateTime  ReleaseDate   get  set                public List lt string gt  ReleaseCountries   get  set         Movie movie   new Movie     movie Name    Bad Boys III    movie Description    It s no Bad Boys     string ignored   JsonConvert SerializeObject movie              Formatting Indented              new JsonSerializerSettings   NullValueHandling   NullValueHandling Ignore       The result will be         Name    Bad Boys III       Description    It s no Bad Boys

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var settings   new JsonSerializerSettings    settings ContractResolver   new CamelCasePropertyNamesContractResolver    settings NullValueHandling   NullValueHandling Ignore    you can add multiple settings and then use it var bodyAsJson   JsonConvert SerializeObject body  Formatting Indented  settings

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An alternate solution using the JsonProperty attribute    JsonProperty NullValueHandling NullValueHandling Ignore      or  JsonProperty  property name   NullValueHandling NullValueHandling Ignore       or for all properties in a class  JsonObject ItemNullValueHandling   NullValueHandling Ignore     As seen in this online doc

[c#] How to ignore a property in class if null, using json.net

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