每次写入Sqlite数据库时重新定义语句 [英] Redefine Statement each time while writing to Sqlite database

问题描述

我编写了一个 java 代码，从名为 edges 的 Sqlite 数据库中的一个表中获取值并将其写入另一个名为 distances 的表中.但是在将值写入表距离时，我每次都必须重新定义语句.如果我不重新定义 Statement 的值，循环将在执行下面给出的代码一次迭代后退出:

I have written a java code to take values from one table in Sqlite Database named edges and write it to another table named distances. But while writing the values to the table distances I have to redefine the Statement each time. If I don't redefine the value of Statement the loop exits after one iteration executing the code given below :

statement.executeUpdate(sql);

但是如果我重新定义语句，循环会按预期继续，即我注释掉的代码行.谢谢.

But if I redefine the Statement the loop continues as expected i.e. the code line which I have commented out.Thank You.

public static Connection dbconn;
public static Statement statement;
public void solve(InputReader in,OutputWriter out) throws ClassNotFoundException
{
    try
    {   
        Class.forName("org.sqlite.JDBC");
        dbconn =DriverManager.getConnection("jdbc:sqlite:/home/src/db.db"); 
        System.out.println("Connected"); 
        statement = dbconn.createStatement(); 
        statement.setQueryTimeout(30);  
        ResultSet rs = statement.executeQuery("select * from edges;"); 
        while(rs.next())
        {
            String sql = "INSERT INTO distances (Road_Name,Start_Latitude,Start_Longitude)" +
                        "VALUES ('"+rs.getString("Road_Name")+"',"+rs.getString("Start_Latitude")+","+rs.getString("Start_Longitude")";

            //Statement statement= dbconn.createStatement(); 
            statement.executeUpdate(sql);
        }
    }
    catch(Exception e)
    {
        System.out.println("Exception : "+e);
    }
}

推荐答案

1. 你不能重用Statement statement，因为它会关闭ResultSet rs;
2. 您不应在 SQL 语句中连接数据.在准备好的语句中使用参数；
3. 为了获得更好的性能，应禁用自动提交并在所有更新调用后显式调用.

我的建议:

public static Connection dbconn;
public static Statement qry;
public void solve(InputReader in,OutputWriter out) throws ClassNotFoundException
{
    try
    {   
        Class.forName("org.sqlite.JDBC");
        dbconn =DriverManager.getConnection("jdbc:sqlite:/home/src/db.db"); 
        System.out.println("Connected"); 
        PreparedStatement upd = dbconn.prepareStatement("INSERT INTO distances (Road_Name,Start_Latitude,Start_Longitude) VALUES (?, ?, ?)");
        dbconn.setAutoCommit(false);
        qry = dbconn.createStatement();
        qry.setQueryTimeout(30);
        ResultSet rs = qry.executeQuery("select * from edges;"); 
        while(rs.next())
        {
            upd.setString(1, rs.getString("Road_Name"));
            upd.setString(2, rs.getString("Start_Latitude"));
            upd.setString(3, rs.getString("Start_Longitude"));
            upd.executeUpdate();
        }
        dbconn.commit();
    }
    catch(Exception e)
    {
        System.out.println("Exception : "+e);
    }
}

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