[JsonSerializer] Provide option to specify a custom default value for a type, property, or field #36236

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1. layomia

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   area-System.Text.Json

   on May 11, 2020
2. layomia

   added this to the 5.0 milestone on May 11, 2020
3. layomia

   self-assigned this

   on May 11, 2020
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5. layomia

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6. layomia

   modified the milestones: 5.0.0, Future on Jun 20, 2020
7. layomia commented on Sep 1, 2020

   

   layomia

   on Sep 1, 2020

   ContributorAuthor

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   From @steveoh in #41630

   Description

   // startup
   .AddJsonOptions(options => {
     options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
     options.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull & JsonIgnoreCondition.WhenWritingDefault;
     options.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter(JsonNamingPolicy.CamelCase));
   });
   
   // ...
   
   [DefaultValue(typeof(decimal), "-1")]
   [DefaultValue(-1.0)]
   [DefaultValue(-1D)]
   public double Prop { 
   	get => _prop;
       set => _prop = Math.Round(value, 2);
   }

   When the prop is set to -1, which is the default value, the property is serialized when JsonIgnoreCondition.WhenWritingDefault is set. I would expect that property to not be serialized.

   Configuration

   osx catalina x64
   5.0.100-preview.8.20417.9
8. walterpg commented on May 19, 2021

   

   walterpg

   on May 19, 2021

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   Raising the flag

   FYI, I am considering returning to a tried-and-true third party to get this functionality. Custom JsonConverters are not sustainable workarounds for my scenarios.
9. eiriktsarpalis commented on Oct 15, 2021

   

   eiriktsarpalis

   on Oct 15, 2021

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   Might need to be considered in conjunction with this proposal: #55781 (comment)
10. eiriktsarpalis commented on Oct 26, 2021

    

    eiriktsarpalis

    on Oct 26, 2021

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    Also related #593 and #40395.
11. eiriktsarpalis commented on Sep 2, 2022

    

    eiriktsarpalis

    on Sep 2, 2022

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    I believe that most of that functionality can now be achieved using a combination of the JsonPropertyInfo.ShouldSerialize/Get/Set delegates in the contract customization layer. There a limits to what values can be specified in the attribute layer, so I'd be inclined to close this in favor of the API surface exposed in #63686.
12. eiriktsarpalis

    closed this as not plannedon Sep 2, 2022
13. ghost locked as resolved and limited conversation to collaborators on Oct 2, 2022