I want to use JsonIgnore only when deserializing with System.Text.Json

[neelabo]

I use Json for the configuration file of the application.
The format of the configuration file changes with the version upgrade of the application, and certain properties may become invalid.
In such cases, we need to make it readable for compatibility with the old configuration file, but we do not want to output to the new configuration file.
I want to be able to do this.

• If it is a JsonIgnore attribute, both serialization and deserialization will be invalid.
• With the IgnoreNullValues ​​option, properties that you want to output as null will also disappear.
• "Conditionally ignore a property" is too heavy for the purpose.

Ideally, doing something like [JsonIgnore(IgnoreDeserialize=false)] would allow for control of serialization and deserialization.

Please consider it.

[ghost]

Area Owners

@layomia, @steveharter, @jozkee

[layomia]

The serializer's features are designed so that data can roundtrip, i.e serialize -> deserialize -> serialize gives the original result. This is why JsonIgnoreAttribute is applied to both serialization and deserialization.

Having a way to specify whether the attribute is applied to serialization/deserialization was considered (see #30687 (comment)), but it wasn't needed by most people.

A future work-around here is to implement a custom converter (for the property) which does the desired null-handling specific to reading and writing. This is blocked by #34439 (planned for 5.0),

[ghost]

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[ghost]

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