Type conversion

When building out Model classes, you may wish to provide a different type of @Column that from the standard supported column types. To recap the standard column types include:

1. String, char, Character
2. All numbers types (primitive + boxed)
3. byte[]/Byte
4. Blob (DBFlow's version)
5. Date/java.sql.Date
6. Bools
7. Model as @ForeignKey
8. Calendar
9. BigDecimal
10. UUID

TypeConverter do not support:

1. Any Parameterized fields.
2. List<T>, Map<T>, etc. Best way to fix this is to create a separate table relationship
3. Conversion from one type-converter to another (i.e JSONObject to Date). The first parameter of TypeConverter is the value of the type as if it was a primitive/boxed type.
4. Conversion from custom type to Model, or Model to a supported type.
5. The custom class must map to a non-complex field such as String, numbers, char/Character or Blob

Define a TypeConverter

Defining a TypeConverter is quick and easy.

This example creates a TypeConverter for a field that is JSONObject and converts it to a String representation:

@com.raizlabs.android.dbflow.annotation.TypeConverter
public class JSONConverter extends TypeConverter<String, JSONObject> {

    @Override
    public String getDBValue(JSONObject model) {
        return model == null ? null : model.toString();
    }

    @Override
    public JSONObject getModelValue(String data) {
        JSONObject jsonObject = null;
        try {
            jsonObject = new JSONObject(data);
        } catch (JSONException e) {
          // you should consider logging or throwing exception.
        }
        return jsonObject;
    }
}

Once this is defined, by using the annotation @TypeConverter, it is registered automatically accross all databases.

There are cases where you wish to provide multiple TypeConverter for same kind of field (i.e. Date with different date formats stored in a DB).

TypeConverter for specific @Column

In DBFlow, specifying a TypeConverter for a @Column is as easy as @Column(typeConverter = JSONConverter.class). What it will do is create the converter once for use only when that column is used.