C# .Net Core 3.1 System.Text.Json Ignore empty collection in serialization

Question

Using Newtonsoft we had a custom resolver for ignoring empty collections. Is there any equivalent configuration for the new system.text.json in .Net core 3.1

Answer 1

Conditionally ignore a property from .NET5's official How to migrate from Newtonsoft.Json to System.Text.Json from 2020 Dec 14 states:

System.Text.Json provides the following ways to ignore properties or fields while serializing:

• The [JsonIgnore] attribute (...).
• The IgnoreReadOnlyProperties global option (...).
• (...) JsonSerializerOptions.IgnoreReadOnlyFields global (...)
• The DefaultIgnoreCondition global option lets you ignore all value type properties that have default values, or ignore all reference type properties that have null values.

These options don't let you:

• Ignore selected properties based on arbitrary criteria evaluated at run time.

For that functionality, you can write a custom converter. Here's a sample POCO and a custom converter for it that illustrates this approach:

(An example of a custom converter for a type follows)

Please note that this converter needs to be a converter for the type that contains the property that is a collection, it's not a converter for the collection type (for that see my 2nd answer).