How to select from database with "where" parameter SpringBoot? - spring-boot

Question

I would like to get one single entry from database. I have such entry model:
#Table("USERS")
data class User(#Id val id: String?, val login: String, val password: String)
and such controller:
#RestController
class MessageResource(val service: MessageService) {
#GetMapping
fun index(): List<User> = service.findMessages()
#PostMapping
fun post(#RequestBody user: User) {
service.post(user)
}
#GetMapping("/user")
fun getByLogin(#RequestParam("login") login: String): User? = service.getByUser(login)
}
such service:
#Service
class MessageService(val db: MessageRepository) {
fun findMessages(): List<User> = db.findMessages()
fun post(user: User) {
db.save(user)
}
fun getByUser(login: String) = db.getByUser(login)
}
and repository:
interface MessageRepository : CrudRepository<User, String> {
#Query("select * from users")
fun findMessages(): List<User>
#Query(value = "select * from users")
fun getByUser(login: String): User? {
val sql = "SELECT * FROM users WHERE login = $login"
return JdbcTemplate().queryForObject(sql, User::class.java)
}
}
I'm little bit new in SprinBoot and I'm trying to get one entry from database. I tried to run it in repository getByUser method, by received error:
org.springframework.dao.IncorrectResultSizeDataAccessException: Incorrect result size: expected 1, actual 4
maybe I did it in wrong way and I have to use another method for filtering all table by row value?

Answer 1

The method JdbcTemplate().queryForObject in repository expected to return only 1 row by the SELECT statement.
If your statement is returning multiple results, you should consider to use JdbcTemplate().query and the getByUser() method in repository should return List<User>.
query doc
fun getByUser(login: String): List<User>? {
val sql = "SELECT * FROM users WHERE login = $login"
return JdbcTemplate().query(sql, new BeanPropertyRowMapper(User::class.java))
}
If you expected only one record returned by database. Here is another easier solution.
If you are using mysql:
fun getByUser(login: String): User? {
val sql = "SELECT * FROM users WHERE login = $login limit 1"
return JdbcTemplate().queryForObject(sql, User::class.java)
}
If you are using Oracle:
fun getByUser(login: String): User? {
val sql = "SELECT * FROM users WHERE login = $login and rownum=1"
return JdbcTemplate().queryForObject(sql, User::class.java)
}