There's all the useless copy and paste tutorials out there that only use the Date object. Congratulations authors, on adding nothing to the world. Then there is the inconsistency on whether the
1. Static, or Instance, @TypeConverter Methods?
1.1. Static Methods
@TypeConverter
public static Long dateToTimestamp(Date date) { ... }
...
}
Generated Code from Static Declaration
public BikeRaceDao_Impl(RoomDatabase __db) {...
final Long _tmp =
DateConverters.dateToTimestamp(
value.getStartDate());
...
}
public class CollectionConverters {
...
}
1.2. Instance Methods
The generated code, made an instance of the CollectionConverters class and used the methods with the instance.
Instance Declaration
public class CollectionConverters {
@TypeConverter
public String stringSetToString(Set<String> stringSet);
...
}
public String stringSetToString(Set<String> stringSet);
...
}
Generated Code from Instance Declaration
public class ProfileFilterDao_Impl implements ProfileFilterDao {
...
private final CollectionConverters __collectionConverters =
...
private final CollectionConverters __collectionConverters =
new CollectionConverters();
...
public ProfileFilterDao_Impl(RoomDatabase __db) {
...
_tmp_1 =
...
public ProfileFilterDao_Impl(RoomDatabase __db) {
...
_tmp_1 =
__collectionConverters.stringSetToString(
value.getCategories());
...
}
}
/**
* Converters for the RoomDatabase.
* This class keeps the Converters for Collections together.
*/
public class CollectionConverters {
@TypeConverter
public static String stringSetToString(
...
}
}
1.3. Conclusion
I would suggest that we use Static methods, with a private constructor to prevent instances of these classes being misused, as per Effective Java 3rd Edition Item Four: Enforce noninstantiability with a private constructor.
2. @TypeConverter methods with Custom Types
As I've said in the Conclusion above, I've gone for static methods with a private constructor. I am using GSON to convert my POJOs to JSON for storage in the database.
/**
* Converters for the RoomDatabase.
* This class keeps the Converters for Collections together.
*/
public class CollectionConverters {
@TypeConverter
public static String stringSetToString(
Set<String> stringSet) {
return (stringSet == null || stringSet.isEmpty()) ?
null : new Gson().toJson(stringSet);
}
@TypeConverter
public static Set<String> stringToStringSet(
}
@TypeConverter
public static Set<String> stringToStringSet(
String string) {
if (string == null || string.isEmpty())
return null;
Type setType =
new TypeToken<HashSet<String>>() {}.getType();
return new Gson().fromJson(string, setType);
}
@TypeConverter
public static String raceTypeSetToString(
Set<RaceType> raceTypeSet) {
return (raceTypeSet == null || raceTypeSet.isEmpty()) ?
null : new Gson().toJson(raceTypeSet);
}
@TypeConverter
public static Set<RaceType> stringToRaceTypeSet(
}
@TypeConverter
public static Set<RaceType> stringToRaceTypeSet(
String string) {
if (string == null || string.isEmpty()) return null;
Type setType =
new TypeToken<HashSet<RaceType>>() {}.getType();
return new Gson().fromJson(string, setType);
}
/**
* Preventing Instancing with a Private Constructor.
*/
private CollectionConverters() {
throw new AssertionError(
}
/**
* Preventing Instancing with a Private Constructor.
*/
private CollectionConverters() {
throw new AssertionError(
"Class should not be instantiated");
}
}
}
}
Thank you for reading and I hope this helped.
