code: public Record findByIds(String tableName, String primaryKey, Object... idValues) {
  		String[] pKeys = primaryKey.split(",");
  		if (pKeys.length != idValues.length)
  			throw new IllegalArgumentException("primary key number must equals id value number");
  		
  		String sql = config.dialect.forDbFindById(tableName, pKeys);
  		List<Record> result = find(sql, idValues);
  		return result.size() > 0 ? result.get(0) : null;
  	}
docs: Find record by ids.
  <pre>
  Example:
  Record user = Db.use().findByIds("user", "user_id", 123);
  Record userRole = Db.use().findByIds("user_role", "user_id, role_id", 123, 456);
  </pre>
  @param tableName the table name of the table
  @param primaryKey the primary key of the table, composite primary key is separated by comma character: ","
  @param idValues the id value of the record, it can be composite id values