Android Room Type Converters For Slighty Complex Data - How to Use

McGuiverTheThings.java

/// start file Linkthing.class - used where your insert data

usage:
  Collection col = new ArrayList();
    col.add(new LP("ddg", "http://duckduckgo"));
    // in db insert routine
    ...setLinkthing(col);
    // You'll get something like this in your db rows .. SELECT * FROM linkthings WHERE links = ' [{"ddg", "http://duckduckgo"}] '
    [{"ddg", "http://duckduckgo"}]
    
    ----=-----
    class LP {
        private String name;
        private String link;
        private void LP(String name, String link) {
            this.name = name;
            this.name = link;
        }

        public String getName() {
            return name;
        }

        public String getLink() {
            return link;
        }
    }
// end file // 

/////start file  JAVA1.class ////
// Fields in your database
...
   @ColumnInfo(name = "linkthing", typeAffinity = ColumnInfo.TEXT)
    private linkThing linkthing;
...
// Getters/Setters
...
  class Converters {
    @TypeConverters(Converters.class)
    public linkThing getLinkthing() {
        return this.linkthing;
    }
    @TypeConverters(Converters.class)
    public void setLinkthing(@NonNull linkThing linkthing) {
        this.linkthing = linkthing;
    }
  }

/////end file////

/////start file  JAVA2.class ////
// database instantiation stuff is a decent place to put this or another file.. below we add the transmogifier

class Converters {
    @TypeConverter
    public static String fromLinkthing(linkThing value) {
        Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
        return value == null ? null : gson.toJson(value);
    }

    @TypeConverter
    public static linkThing fromString(String value) {
        Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
        return value == null ? null : gson.fromJson(value, linkThing.class);
    }
}
/////end file////

// Info about HashMap serialize to stream.. try typeAffinity = ColumnInfo.BLOB for this sort of thing, there be dragons
GSON - gson.excludeFieldsWithoutExposeAnnotation().create(); // learn how gson can `excludeFieldsWithoutExposeAnnotation`
https://www.techrepublic.com/blog/software-engineer/use-gson-to-work-with-json-in-your-android-apps/
https://beginnersbook.com/2013/12/how-to-serialize-hashmap-in-java/