使用预准备语句的选择性更新

Question

I have one function which updates a MySQL table. I need to do a selective update of fields according to whether the parameters are present or not. This is how I have coded it right now.

        String sql =  "";
        if (employerId > 0) sql = sql + "employerid=?,";
        if (status != null) sql += " status=?,";
        if(printurl != null) sql += " url=?";
        if (sql.endsWith(",")) sql = sql.substring(0, sql.length()-1);
        PreparedStatement ps = con.prepareStatement("update employer set "
                + sql
                + "where id=?");

       if (employerId > 0) ps.setInt(1, employerId);
       if (status != null) ps.setString(2,status);

When I do like this, how do I determine the parameter index? According to the parameters present (if conditions), the parameter index will also vary, right? How do I get around with this? Is there a better way to handle this in Java?

Answer 1

Can you please try a static query as below?

String sql =  "update employer set employerid=IF(?=0,employerid,?),"+
              "status=IFNULL(?,status), url=IFNULL(?,url) " +
              "where id=?";

Conceptually, I am suggesting to update the column with itself if it is 0 or null . This way, you don't need to create dynamic query string or dynamically set the parameters.

Answer 2

The SqlBuilder library provides a much better way to do dynamic SQL query generation in java programs. The QueryPreparer class specifically addresses the problem you are encountering here by tracking the indexes for you.

disclaimer, i am the primary developer of the SqlBuilder project.

Answer 3

How about using arraylist ? When you first checking whether paramaters are existed, add to arraylist. After that, iterating array list and set parameters. In this case,

it determines not only the parameter index but also avoids for checking parameter existed again.

Like that

List paramList = new ArrayList<Object>();

         if (employerId > 0) {
             sql = sql + "employerid=? ,";
             paramList.add(employerId);
         }
         if (status != null) { 
             sql += " status=? ,";
             paramList.add(status);
         }
         if(printurl != null) {
             sql += " url=? ";
             paramList.add(printurl);
         }
         if (sql.endsWith(",")) 
             sql = sql.substring(0, sql.length()-1);

         PreparedStatement ps = con.prepareStatement("update employer set " + sql + "where id=?");

         for(int i=0; i< paramList.size(); i++) {
             if(paramList.get(i) instanceof Integer) {
                 ps.setInt((i + 1), (Integer)paramList.get(i));
             }
             else if(paramList.get(i) instanceof String) {
                 ps.setString((i + 1), (String)paramList.get(i));
             }
         }
         System.out.println(ps);

Answer 4

please see the following code:

       String sql =  "update employer set ";
        boolean hasParam = false;
        if (employerId > 0){
                sql += " employerid=? ";
                hasParam = true;
        }
        if (status != null){
            if(hasParam){
                sql += " , ";
            }
            sql += " status=? ";
            hasParam = true;
        }
        if(printurl != null){
            if(hasParam){
                sql += " , ";
            }
            sql += " url=?";
        }
        sql += " where id=?";
        PreparedStatement ps = con.prepareStatement(sql);

       int index = 1;
       if(employerId > 0){
           ps.setInt(index++, employerId);
       }
       if(status != null){
           ps.setString(index++, status);
       }
       if(printurl != null){
           ps.setString(index++, printurl);
       }
       ps.setInt(index, id);