[英]Insert time and date in MySQL database using jsp,bean class and servlet
[英]how to list all elements of class when class have foreign key of another class in jdbc servlet jsp mysql?
當類具有另一個類字段時,如何在Java中列出類元素? 看起來像這樣:
public class Grad {
private int grad_id;
private **Drzava drzava**;
private String naziv;
private boolean aktivan;
private Set<Korisnik> korisnici = new HashSet<Korisnik>(0);
public Drzava getDrzava() {
return drzava;
}
public void setDrzava(Drzava drzava) {
this.drzava = drzava;
}
public List<Grad> getAllGrad() {
List<Grad> gradovi = new ArrayList<Grad>();
try {
Statement statement = DBConnection.getConnection().createStatement();
ResultSet rs = statement.executeQuery("select * from grad;");
while (rs.next()) {
Grad grad = new Grad();
grad.setGrad_id(rs.getInt("grad_id"));
**grad.setDrzava( (Drzava)rs.getObject("drzava"));**/**(HERE IS A PROBLEM!!)**/
grad.setNaziv(rs.getString("naziv"));
grad.setAktivan(rs.getBoolean("aktivan"));
gradovi.add(grad);
}
else if (action.equalsIgnoreCase("listGrad")){
forward = LIST_GRAD;
request.setAttribute("gradovi", dao.getAllGrad());
這是在jsp頁面中,我認為該錯誤位於grad.drzava.naziv:
<c:forEach items="${gradovi}" var="grad">
<tr>
<td><c:out value="${grad.grad_id}"/></td>
<td><c:out value="${grad.drzava.naziv}"/></td>
<td><c:out value="${grad.naziv}" /></td>
<td><c:out value="${grad.aktivan}" /></td>
異常是:java sql SQLException找不到列'drzava'。
非常感謝您的回答:))
ResultSet rs = statement.executeQuery("select * from grad;");
這將返回“ Drzava”表的主鍵,即grad表中的外鍵。 因此,要獲取Drzava類對象,您需要再次執行另一個查詢,例如:
ResultSet rs = statement.executeQuery("select * from drzava;");
然后將所得的drzava類對象分配給grad類變量。
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