checklist.md

Common mistakes (jv-dao-service)

• Run mvn clean package after finish homework and before sending the solution.

• Use PreparedStatement over Statement, even for a static query with no parameters in getAll() method. It's the best practice, and it's slightly faster.

• Use wrapper for id: Long id but not long id. And remember what is the difference between == and equals.

• Remember about SQL style: use uppercase for SQL keywords in your queries.

  • Wrong:

      SELECT * from manufacturers WHERE is_deleted = false;   

  • Good:

      SELECT * FROM manufacturers WHERE is_deleted = FALSE;

• Use aliases for table names in SQL queries with JOIN

  • Wrong:

      SELECT cars.id AS car_id, manufacturers.id AS manufacturer_id
          FROM cars
          JOIN manufacturers ON cars.manufacturer_id = manufacturers.id
        WHERE...;                     

  • Good:

      SELECT c.id AS car_id, m.id AS manufacturer_id
        FROM cars c
          JOIN manufacturers m ON c.manufacturer_id = m.id
        WHERE...;

• Use informative messages for exceptions.

  • Wrong:

          throw new DataProcessingException("Can't get manufacturer", e);

  • Good:

          throw new DataProcessingException("Can't get manufacturer by id " + id, e);
          throw new DataProcessingException("Can't insert manufacturer " + manufacturer, e);

• To display data while testing use Stream API forEach(), not for loop.

• get() methods in Dao layer should return Optional (not in services). In the service layer better call method get() on Optional and return the object.

• You should not have any additional logic on Dao layer except managing database operations. All business logic must be on service layer.

• Do not open connection to DB on the service layer.