可以使用JDBC从数据库中检索一条记录，但不能检索另一条记录

Question

So, for a school project, I am building a discord bot. One of the features that I have built in is that he can retrieve gif links from a MySQL database, and send them in a message. Now, my issue is that I am only able to retrieve one record from my database, and no other records. If I put the query that I use into MySQL workbench and run it, it will retrieve those records.

This is the method for retrieving the gifs

public static ArrayList<Gif> GetGifsFromDB(String msg){
    ArrayList<Gif> gifs = new ArrayList<>();

    try(Connection conn = (Connection)DriverManager.getConnection(url, userName, password)){
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        Statement stmnt = conn.createStatement();
        String sql = "Select * from gif WHERE Type = '" + msg + "'";
        stmnt.execute(sql);

        try(ResultSet rs = stmnt.getResultSet()){
            while(rs.next()){
            Gif g = new Gif();
            g.setID(rs.getInt("GifID"));
            g.setURL(rs.getString("GifURL"));
                System.out.println(g.getID() + g.getURL());
            gifs.add(g);
        }
        rs.close();
        conn.close();
        }

    }
    catch(SQLException ex){
        System.err.println(ex.getMessage());
    }
    catch(Exception ex){
        System.err.println(ex.getMessage());
    }

    return gifs;
}

The "Type" in the database it just a category. With the test data I have in there, the 3 types are no, surprised and lonely. Only no returns a gif.

Answer 1

Remove closing ResultSet and Connection lines:

 rs.close();
 conn.close();

You are already closing it using try-with-resources

Answer 2

Issue ended up being with MySql not committing records to the database. Once workbench was refreshed, the added records disappeared. Rather strange that even though the records weren't in the database, they could be retrieve.

Answer 3

Most likely your msg is not exactly matching with any of the values for the database Type column.

Test by running

SELECT COUNT(*) FROM gif WHERE Type = '... put msg content here ...'

Do this manually directly on the database.

You can also try to put following line of code at the end:

System.out.println("Number of Selected Gifs: "+gifs.size());

If either of those results zero, then it means that msg was not exactly matched with Type . Maybe uppercase/lowercase issue?

Also to avoid SQL Injection, and other issues, please strongly consider using bind variables using a PreparedStatement .