Can I make json4s's extract method case insensitive? - scala

Question

I am using case classes to extract json with json4s's extract method. Unfortunately, the Natural Earth source data I am using isn't consistent about casing... at some resolutions a field is called iso_a2 and at some it's ISO_A2. I can only make json4s accept the one that matches the field in the case class:
object TopoJSON {
case class Properties(ISO_A2: String)
...
// only accepts capitalised version.
Is there any way to make json4s ignore case and accept both?

Answer 1

There is no way to make it case insensitive using the configuration properties, but a similar result can be achieved by either lowercasing or uppercasing the field names in the parsed JSON.
For example, we have our input:
case class Properties(iso_a2: String)
implicit val formats = DefaultFormats
val parsedLower = parse("""{ "iso_a2": "test1" }""")
val parsedUpper = parse("""{ "ISO_A2": "test2" }""")
We can lowercase all field names using a short function:
private def lowercaseAllFieldNames(json: JValue) = json transformField {
case (field, value) => (field.toLowerCase, value)
}
or make it for specific fields only:
private def lowercaseFieldByName(fieldName: String, json: JValue) = json transformField {
case (field, value) if field == fieldName => (fieldName.toLowerCase, value)
}
Now, to extract the case class instances:
val resultFromLower = lowercaseAllFieldNames(parsedLower).extract[Properties]
val resultFromUpper = lowercaseAllFieldNames(parsedUpper).extract[Properties]
val resultByFieldName = lowercaseFieldByName("ISO_A2", parsedUpper).extract[Properties]
// all produce expected items:
// Properties(test1)
// Properties(test2)
// Properties(test2)