When objects returned in search results are deserialized, they are instantiated by the JSON.NET serializer. If you require a custom action when instantiating the objects, customize the instantiation with the Client conventions.
An example of configuring custom instantiation can look like this:
//using EPiServer.Find.ClientConventions; client.Conventions.ForType<BlogPost>() .CreateUsing(() => new BlogPost("someCtorParamValue"));
If indexed objects are so complex that they require custom instantiation, they are often not suitable as search results. It might be better to project the search results to another, simpler class using the Select method.
Updated 3 months ago