Jooq reactive fetching using r2dbc driver

When using jOOQ reactively, you should never call any blocking methods, such as ResultQuery.fetchOneInto(Class). That method is just a convenience method for ResultQuery.fetchOne() and then Record.into(Class). Nothing keeps you from calling Record.into(Class) yourself, neither in the blocking world, nor in the non-blocking world.

So, use your usual reactor library methods to map stream contents:

mono.map { r -> r.into(UserCredentialsModel::class.java) }

Or, in a complete example:

return Mono.from {
    dsl.select(
            USER_CREDENTIALS.ID,
            USER_CREDENTIALS.EMAIL,
            USER_CREDENTIALS.PHONE,
            USER_CREDENTIALS.LOGIN,
            USER_CREDENTIALS.PASSWORD)
        .from(USER_CREDENTIALS)
        .where(USER_CREDENTIALS.ID.eq(id))
        .and(USER_CREDENTIALS.IS_ACTIVE.eq(true))
} .map { r -> r.into(UserCredentialsModel::class.java) }

Without testing I would say it should be

return Mono.from(
    dsl.select(
            USER_CREDENTIALS.ID,
            USER_CREDENTIALS.EMAIL,
            USER_CREDENTIALS.PHONE,
            USER_CREDENTIALS.LOGIN,
            USER_CREDENTIALS.PASSWORD)
        .from(USER_CREDENTIALS)
        .where(USER_CREDENTIALS.ID.eq(id))
        .and(USER_CREDENTIALS.IS_ACTIVE.eq(true)));