将 JdbcTemplate 与 Lamda RowMapper 一起使用的更好方法

Question

我经常使用 jdbcTemplate.query 不是 return 结果集，而是访问数据库并对每个选定的记录进行一些计算。例如下面的代码有效

    Map<String, Double> mAcc = new HashMap<>();
    sql = "select ar.id_codice_art, sum(ar.quantita) quantita\n" +
            "from accettazione a \n" +
            "inner join accettazione_riga ar on a.id_accettazione = ar.id_accettazione\n" +
            "where a.id_ordine = ? \n" +
            "group by ar.id_codice_art";
    jdbcTemplate.query(sql, (rs, i)->{
        mAcc.put(rs.getString("id_codice_art"), rs.getDouble("quantita"));
        return "";
    }, idOrdine);

但它并不干净，尤其是当 return "" 时，因为 RowMapper 接口需要它。同时，我不想创建记录或 class 只是为了 return 列表并在列表上工作。

是否有更好的方法来使用 jdbcTemplate 进行同样的思考？

Answer 1

You can try using the following code. Just create a new map, insert values in it and return it. and then you can copy values from that result map to your map.

 Map<String, Double> mAcc = new HashMap<>();
    sql = "select ar.id_codice_art, sum(ar.quantita) quantita\n" +
            "from accettazione a \n" +
            "inner join accettazione_riga ar on a.id_accettazione = ar.id_accettazione\n" +
            "where a.id_ordine = ? \n" +
            "group by ar.id_codice_art";
    Map<String,Double> = jdbcTemplate.query(sql, (rs)->{
    Map<String,Double> map = new HashMap<>();
        while(rs.next()){
        map.put(rs.getString("id_codice_art"), rs.getDouble("quantita"));
        }
        return map;
    }, idOrdine);

Answer 2

我假设 idOrdine 键是 Long。

Map<String, Double> mAcc = new HashMap<>();
PreparedStatementSetter pss = ps -> ps.setLong(1, idOrdine);
RowCallbackHandler rch = rs -> mAcc.put(rs.getString("id_codice_art"),
     rs.getDouble("quantita"));
jdbcTemplate.query(sql, pss, rch);

当然，您可以 in-line 那些 lambda 以避免导入这两个类。

我刚刚在研究您的答案时了解到这一点，现在我将重写我刚刚为工作编写的一大块代码，以也使用该方法！

将 JdbcTemplate 与 Lamda RowMapper 一起使用的更好方法

Better way to use JdbcTemplate with Lamda RowMapper

java

spring

jdbctemplate