Question

使用JSoup解析HTML，然后将行插入MS SQL Server数据库。为了避免重复，我需要在插入执行之前检查guid是否存在。代码工作，但我无法对guid进行验证。请参阅插入块中的Select语句。返回以下错误：

线程中的异常＆＃34; main＆＃34; com.microsoft.sqlserver.jdbc.SQLServerException：多部分标识符＆＃34; FeedMessage.guid＆＃34;无法受约束。在 com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDatabaseError（SQLServerException.java:216）在 com.microsoft.sqlserver.jdbc.SQLServerStatement.getNextResult（SQLServerStatement.java:1515）在 com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.doExecutePreparedStatement（SQLServerPreparedStatement.java:404）在 com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement $ PrepStmtExecCmd.doExecute（SQLServerPreparedStatement.java:350）在 com.microsoft.sqlserver.jdbc.TDSCommand.execute（IOBuffer.java:5696）在 com.microsoft.sqlserver.jdbc.SQLServerConnection.executeCommand（SQLServerConnection.java:1715）在 com.microsoft.sqlserver.jdbc.SQLServerStatement.executeCommand（SQLServerStatement.java:180）在 com.microsoft.sqlserver.jdbc.SQLServerStatement.executeStatement（SQLServerStatement.java:155）在 com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.executeUpdate（SQLServerPreparedStatement.java:314）在Archiver.Database.writer（Database.java:58）at RSS.Test.main（Test.java:35）Java结果：1

    // Need to use this class for all of the DB-related interactions. 
    // Add methods to this class for added capabilities from within the GUI
package Archiver;

import RSS.FeedMessage;
import RSS.Test;
import Scraper.Scraping;
import java.sql.*;

/**
 *
 * @author joel.ramsey
 */
public class Database {

    Statement stmt;

    String DriverName;
    String url = "jdbc:sqlserver://sss.ss.ss.ss:1433;databaseName=TextAnalytics";
    String DBuser = "xx";
    String DBpassword = "xxxxxx";

    //Method to connect to the DB upon initialization
    public void connectionText() throws ClassNotFoundException, SQLException {

        try (Connection con = DriverManager.getConnection(this.url, this.DBuser, this.DBpassword);) {

            if (con != null) {
                DatabaseMetaData dm = (DatabaseMetaData) con.getMetaData();
                System.out.println("Driver name: " + dm.getDriverName());
                System.out.println("Driver version: " + dm.getDriverVersion());
                System.out.println("Product name: " + dm.getDatabaseProductName());
                System.out.println("Product version: " + dm.getDatabaseProductVersion());
            }

        } catch (Exception e) {
            System.err.println("Got an exception...");
            System.err.println(e.getMessage());

        }

    }

    //Method to write the parsed content of the RSS source article to the DB.
    public void writer(String Title, String Description, String Link, String Author, String guid, String contents) throws SQLException, ClassNotFoundException {
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        Connection con = null;
        PreparedStatement writeStmt = null;
        ResultSet rs = null;
        try {
            con = DriverManager.getConnection(this.url, this.DBuser, this.DBpassword);
            writeStmt = con.prepareStatement("IF NOT EXISTS (SELECT TextAnalytics FROM Archive_Source WHERE guid = FeedMessage.guid) INSERT INTO Archive_Source(title,description,link,author,guid,contents) VALUES (?,?,?,?,?,?)");
            writeStmt.setString(1, Title);
            writeStmt.setString(2, Description);
            writeStmt.setString(3, Link);
            writeStmt.setString(4, Author);
            writeStmt.setString(5, guid);
            writeStmt.setString(6, contents);
            writeStmt.executeUpdate();
        } finally {
            close(con, writeStmt, rs);
        }
    }

    //Method to close the connection manually. Called at the conclusion of each DB contact job.
    protected void close(Connection conn, Statement stmt, ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
            }
        }
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
            }
        }
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
            }
        }
    }

    //Method to delete all contents from the table. Should be called from the GUI
    public void delete(String Title, String Description, String Link, String Author, String guid, String contents) throws SQLException, ClassNotFoundException {
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        Connection con = null;
        PreparedStatement writeStmt = null;
        ResultSet rs = null;
        try {
            con = DriverManager.getConnection(this.url, this.DBuser, this.DBpassword);
            writeStmt = con.prepareStatement("DELETE * FROM Archive_Source");
            writeStmt.executeUpdate();
        } finally {
            close(con, writeStmt, rs);
        }
    }
}

Answer 1

您的SQL语句中有几个错误。我把它分成了几行，所以答案更容易阅读。

" IF NOT EXISTS (SELECT TextAnalytics FROM Archive_Source " +
" WHERE guid = FeedMessage.guid) INSERT INTO " +
" Archive_Source(title,description,link,author,guid,contents) " +
" VALUES (?,?,?,?,?,?)") "

什么是FeedMessage.guid？如果FeedMessage是一个表，则需要在FROM语句中引用它。
您正在为INSERT语句参数设置值，但不为guid函数参数设置值。在您说WHERE guid = FeedMessage.guid的部分中，您也不应该参数化guid，或者像这样连接值。 "WHERE '" + guid + "'= FeedMessage.guid"。

因此，如果我对您的代码的假设是正确的，则代码应如下所示。

    try {
        con = DriverManager.getConnection(this.url, this.DBuser, this.DBpassword);
        writeStmt = con.prepareStatement(
                         " IF NOT EXISTS (SELECT TextAnalytics " +
                         " FROM Archive_Source WHERE guid = ?) " +
                         " INSERT INTO Archive_Source " +                                                          
                         " (title,description,link,author,guid,contents) " +
                         " VALUES (?,?,?,?,?,?) )";
        writeStmt.setString(1, guid);
        writeStmt.setString(2, Title);
        writeStmt.setString(3, Description);
        writeStmt.setString(4, Link);
        writeStmt.setString(5, Author);
        writeStmt.setString(6, guid);
        writeStmt.setString(7, contents);
        writeStmt.executeUpdate();
    } finally {
        close(con, writeStmt, rs);
    }

注意我删除了FeedMessage.guid并将其替换为guid参数，并假设该比较的左侧是guid表中名为Archive_Source的字段。

在插入SQL Server之前检查列值是否存在

1 个答案: