> For the complete documentation index, see [llms.txt](https://educacion.gitbook.io/programacion/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://educacion.gitbook.io/programacion/ud8-persistencia-en-bases-de-datos/escenario-de-traballo/creando-a-capa-de-dao-con-statement.md).

# Creando a capa de DAO con Statement

A capa DAO ten a responsabilidade de realizar o acceso a datos da aplicación, mapeando o contido da base de datos a súa clase correspondente da capa Modelo ou Entity.

Cando empregamos o **patrón DAO, é habitual que para cada clase do modelo, exista a súa clase de acceso a datos.** A continuación mostrase un exemplo de operacións CRUD para Alumno: 

```java
package DAO;

import Util.Lector;
import Modelo.Alumno;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public class AlumnoDAOImpl {

    public List<Alumno> findAll() {
        List<Alumno> lista = new ArrayList<>();
        String sql = "SELECT * FROM alumnos";
        try (Connection con = DriverManager.getConnection(Lector.getInstancia().getServidor(), Lector.getInstancia().getUsuario(), Lector.getInstancia().getContraseña());
                Statement s = con.createStatement()){
            ResultSet rs = s.executeQuery(sql);
            while (rs.next()){
            //Es posible hacer el get por el valor del campo y por el valor del id
                /*Alumno alumno = new Alumno(
                        rs.getInt("id"),
                        rs.getString("nombre"),
                        rs.getString("apellido"),
                        rs.getDate("fechaNac").toLocalDate()
                );*/
                Alumno alumno = new Alumno(
                        rs.getInt(1),
                        rs.getString(2),
                        rs.getString(3),
                        rs.getDate(4).toLocalDate()
                );
                lista.add(alumno);
            }

        } catch (SQLException e){
            System.out.println(e.getMessage());
        }
        return lista;
    }


    public Optional<Alumno> findById(int id) {
        Optional<Alumno> res;
        String sql = "SELECT * FROM alumnos WHERE id = " + id;
        try (Connection con = DriverManager.getConnection(Lector.getInstancia().getServidor(), Lector.getInstancia().getUsuario(), Lector.getInstancia().getContraseña());
        Statement s = con.createStatement()){
            ResultSet rs = s.executeQuery(sql);

            if (rs.next()){
                Alumno alumno = new Alumno(
                        rs.getInt("id"),
                        rs.getString("nombre"),
                        rs.getString("apellido"),
                        rs.getDate("fechaNac").toLocalDate()
                );
                res = Optional.of(alumno);
                return res;
            }

        } catch (SQLException e){
            System.out.println(e.getMessage());
        }
        return Optional.empty();
    }

    public int insert(Alumno a) {
        String sql = "INSERT INTO alumnos (nombre, apellido, fechaNac) VALUES (" +
                "'" + a.getNombre() + "', " +
                "'" + a.getApellido() + "', " +
                "'" + a.getFechaNac().toString() + "')";
        try (Connection con = DriverManager.getConnection(Lector.getInstancia().getServidor(), Lector.getInstancia().getUsuario(), Lector.getInstancia().getContraseña());
             Statement s = con.createStatement()) {

            int filasAfectadas = s.executeUpdate(sql, Statement.RETURN_GENERATED_KEYS);

            if (filasAfectadas > 0) {
                ResultSet rs = s.getGeneratedKeys();
                if (rs.next()) {
                    int id = rs.getInt(1);
                    a.setId(id);
                    return id;
                }
                return -1;
            }
        } catch (SQLException e) {
            System.out.println(e.getMessage());
        }
        return -1;
    }

    public Optional<Alumno> update(Alumno a) {
        String sql = "UPDATE alumnos SET " +
                "nombre = '" + a.getNombre() + "', " +
                "apellido = '" + a.getApellido() + "', " +
                "fechaNac = '" + a.getFechaNac().toString() + "' " +
                "WHERE id = " + a.getId();
        try (Connection con = DriverManager.getConnection(Lector.getInstancia().getServidor(), Lector.getInstancia().getUsuario(), Lector.getInstancia().getContraseña());
             Statement s = con.createStatement()) {

            int filasAfectadas = s.executeUpdate(sql);
            if (filasAfectadas > 0) {
                return Optional.of(a);
            }
        } catch (SQLException e) {
            System.out.println(e.getMessage());
        }
        return Optional.empty();
    }

    public boolean remove(int id) {
        String sql = "DELETE FROM alumnos WHERE id = " + id;
        try (Connection con = DriverManager.getConnection(Lector.getInstancia().getServidor(), Lector.getInstancia().getUsuario(), Lector.getInstancia().getContraseña());
             Statement s = con.createStatement()) {
            int filasAfectadas = s.executeUpdate(sql);
            return filasAfectadas > 0;

        } catch (SQLException e) {
            System.out.println(e.getMessage());
        }
        return false;

    }
}

```


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