JDBC pobiera atrybut relacja +, do którego odnosi się klucz obcy

Question

Czy można uzyskać cel FK z JDBC?

Mam tylko relacja źródło + Atrybuty metodą getExportedKeys:

ResultSet fksE = dbm.getExportedKeys(conn.getCatalog(), null, "SourceRelName"); 
String fkTableNameE = fksE.getString("FKTABLE_NAME"); 
String fkColumnNameE = fksE.getString("FKCOLUMN_NAME"); 

Potem próbowałem za pomocą metody getImportedKeys, ale nie zrobił praca.

Oto moja klasa:

public class DbConnection { 

    private String userName = null; 
    private String password = null; 
    private String driver = null; 
    private String DbUrl = null; 
    private Connection conn = null; 
    private DatabaseMetaData dbm = null; 
    private ArrayList<String> relationNames = null; 
    private ResultSet tables = null; 
    private Database database = null; 

    public DbConnection(String user, String pwd, dbaCore.data.dBTypes.TypeEnum type, String url) { 
    userName = user; 
    password = pwd; 
    switch (type) { 
     case MYSQL: 
     driver = "com.mysql.jdbc.Driver"; 
     break; 
     case POSTGRES: 
     break; 
     case MSDB: 
     break; 
     case ORACLE: 
     break; 
     case SQLITE: 
     break; 
    } 
    DbUrl = url; 
    database = new Database(); 
    relationNames = new ArrayList<>(); 

    try { 
     Class.forName(driver).newInstance(); 
     conn = DriverManager.getConnection(DbUrl, userName, password); 
     System.out.println("Database connection established"); 

     //Get Relation Names 
     dbm = conn.getMetaData(); 
     String[] types = {"TABLE"}; 
     tables = dbm.getTables(null, null, "%", types); 
     while (tables.next()) { 
     String table = tables.getString("TABLE_NAME"); 
     relationNames.add(table); 
     } 

     //Get Attributes 
     for (String relation : relationNames) { 
     RelationSchema tmpRelation = new RelationSchema(relation); 

     Statement st = conn.createStatement(); 
     ResultSet rs = st.executeQuery("SELECT * FROM " + relation); 
     ResultSetMetaData md = rs.getMetaData(); 
     int col = md.getColumnCount(); 
     System.out.println("ATTRIBUTES: "); 
     for (int i = 1; i <= col; i++) { 
      String col_name = md.getColumnName(i); 
      System.out.println(col_name); 
      tmpRelation.addAttribute(col_name); 
     } 
     ResultSet pks = dbm.getPrimaryKeys(null, null, relation); 
     while (pks.next()) { 
      String columnName = pks.getString("COLUMN_NAME"); 
      System.out.println("Primary Key: " + columnName); 
      tmpRelation.getAttributeByName(columnName).setIsPrimaryKey(true); 
     } 
     database.addRelationSchema(tmpRelation); 
     } 

     //Get Foreignkeys 
     for (String relation : relationNames) { 
     ResultSet fksE = dbm.getExportedKeys(conn.getCatalog(), null, relation); 

     while (fksE.next()) { 
      String fkTableNameE = fksE.getString("FKTABLE_NAME"); 
      String fkColumnNameE = fksE.getString("FKCOLUMN_NAME"); 
     ResultSet fksI = dbm.getImportedKeys(conn.getCatalog(), null, fkTableNameE); 
     String fkTableNameI = fksI.getString("FKTABLE_NAME"); 
     String fkColumnNameI = fksI.getString("FKCOLUMN_NAME"); 

     System.out.println("FKTABLE_NAME_E: " + fkTableNameE + " - FKCOLUMN_NAME_E: " + fkColumnNameE); 
     System.out.println("FKTABLE_NAME_I: " + fkTableNameI + " - FKCOLUMN_NAME_I: " + fkColumnNameI); 
    } 
    } 

} catch (Exception e) { 
    System.err.println("Cannot connect to database server"); 
    e.printStackTrace(); 
} 
finally 
{ 
    if (conn != null) { 
    try { 
     conn.close(); 
     System.out.println("Database connection closed"); 
    } catch (Exception e) { 
     e.printStackTrace(); 
    } 
    } 
} 


} 

Answer 1

getImportedKeys pracuje dla mnie. Kod:

private static void printForeignKeys(Connection connection, String tableName) throws SQLException { 
    DatabaseMetaData metaData = connection.getMetaData(); 
    ResultSet foreignKeys = metaData.getImportedKeys(connection.getCatalog(), null, tableName); 
    while (foreignKeys.next()) { 
     String fkTableName = foreignKeys.getString("FKTABLE_NAME"); 
     String fkColumnName = foreignKeys.getString("FKCOLUMN_NAME"); 
     String pkTableName = foreignKeys.getString("PKTABLE_NAME"); 
     String pkColumnName = foreignKeys.getString("PKCOLUMN_NAME"); 
     System.out.println(fkTableName + "." + fkColumnName + " -> " + pkTableName + "." + pkColumnName); 
    } 
}