How to change JSON returned by query using Helidon 2.0.0-M-2 - helidon

Question

I'm using Helidon 2.0.0-M2.
When I run the query below I get back a list of JSON objects.
dbClient.execute(exec -> exec.createNamedQuery("select-dsitem-by-id")
.addParam("userId", dataItemId)
.execute())
.thenAccept(response::send)
.exceptionally(throwable -> sendError(throwable, response));
Returned list
[
{
"data": "qwerty",
"user_id": "12345"
},
{
"data": "qwerty123",
"user_id": "22345"
}
]
The attribute names seem to be taken directly from the database column name. e.g. one attribute name returned is "user_id". However, I want it to be "userId". I also want to create a parent wrapper for this list like:
{
"userList": [
{
"data": "qwerty",
"user_id": "12345"
},
{
"data": "qwerty123",
"user_id": "22345"
}
]
}
What is the best way to do this with the dbclient?
Thanks

Answer 1

Simple approach:
Change your SQL statement to return the correct name, such as:
SELECT data, user_id as userId FROM mytable
Complicated approach:
We are working on a better support to map to a JSON stream.
Currently there is only one (a bit complicated) way to achieve this:
You can create a custom mapper from a DbRow to JsonObject. This mapper needs to be a general one (it must work for any DbRow of any query).
The built-in mapper uses metadata provided on the columns. I have prepared a simple example (that just expects to have a single type of statements):
class DbRecordMapperProvider implements DbMapperProvider {
private static final DbMapper<JsonObject> MAPPER = new DbRecordMapper();
#SuppressWarnings("unchecked")
#Override
public <T> Optional<DbMapper<T>> mapper(Class<T> aClass) {
if (JsonObject.class.equals(aClass)) {
return Optional.of((DbMapper<T>)MAPPER);
}
return Optional.empty();
}
}
class DbRecordMapper implements DbMapper<JsonObject> {
#Override
public JsonObject read(DbRow dbRow) {
return Json.createObjectBuilder()
.add("name", dbRow.column("FIRSTPART").as(String.class))
.add("message", dbRow.column("SECONDPART").as(String.class))
.build();
}
#Override
public Map<String, ?> toNamedParameters(JsonObject dbRecord) {
return dbRecord;
}
#Override
public List<?> toIndexedParameters(JsonObject dbRecord) {
throw new IllegalStateException("Cannot convert json object to indexed parameters");
}
}
The important method is public JsonObject read(DbRow dbRow).
Once you have such a DbMapperProvider, you register it with the DbClient:
dbClient = DbClient.builder()
.config(config.get("db"))
.mapperProvider(new DbRecordMapperProvider())
.build();