将 if-chain 转换为基于规则的字典

Question

我坚持将一个巨大的 if 链转换为字典。在旧版解决方案中，Excel 导出是这样完成的：

foreach (DataRow dr in fullData.Rows)
{
    DataRow newRow = dt.NewRow();

    foreach (DataColumn dc in dt.Columns)
    {
        String s = dc.Caption;

        if (s.Equals("ID"))
            newRow[dc] = dr["id"];
        else if (s.Equals("PQ-Nr"))
            newRow[dc] = dr["pqNummer"];
        else if (s.Equals("GJ"))
            newRow[dc] = dr["geschaeftsjahr"];
        else if (s.Equals("Link"))
            newRow[dc] = dr["link"];
        /*more complex example*/
        else if(s.Equals("GF"))
        {
            string content = "";
            int intVal = 0;
            if (Int32.TryParse(dr["id"].ToString(), out intVal))
            {
                List<Freigabe> liste = DBHelper.getFreigabenByPersonalTyp(intVal, Personal.GF);
                foreach (Freigabe f in liste)
                {
                //build content string here
                }
            }
            newRow[dc] = content.TrimEnd();
        }
        /*plus around 60 more else if statements*/
    }
    dt.Rows.Add(newRow);
}
return dt;

我的想法是将规则和实际分配的行分成两部分。所以我创建了一个字典：

var rules = new Dictionary<Func<string, bool>, Func<DataRow, object>>()
{
    {y => y == "ID", x =>  x["id"] },
    {y => y == "PQ-Nr", x => x["pqNummer"] },
    //....
};

为了获取当前列值，我执行以下操作：

foreach (DataRow dr in fullData.Rows)
{
    DataRow newRow = dt.NewRow();

    foreach (DataColumn dc in dt.Columns)
    {
        String s = dc.Caption;

        newRow[dc] = from r in rules
                     where r.Key(s)
                     select r.Value(dr);
    }
    dt.Rows.Add(newRow);
}
return dt;

完成报告中每个单元格的内容现在是：System.Linq.Enumerable+WhereSelectEnumerableIterator2[System.Collections.Generic.KeyValuePair2[System.Func2[System.String,System.Boolean],System.Func2[System.Data.DataRow,System.Object]],System.Object]，而不是它的价值。

我到底做错了什么？

Answer 1

我建议更改rules类型：

// No lambdas, just string to string
Dictionary<String, String> rules = new Dictionary<String, String>() {
  {"ID", "id"},
  {"PQ-Nr", "pqNumme"},
  {"GJ", "geschaeftsjahr"},
  {"Link", "link"},
  //TODO: put other rules here
};

所以

foreach (DataRow dr in fullData.Rows) {
    DataRow newRow = dt.NewRow();

    foreach (DataColumn dc in dt.Columns)
        newRow[dc] = dr[rules[dc.Caption]];

    dt.Rows.Add(newRow);
}

编辑：如果有复杂的规则（如编辑问题中的"GF" 之一）Dictionary<String, String> rule 也可以提供帮助：

   foreach (DataColumn dc in dt.Columns) {
     String rule;

     if (rules.TryGetValue(dc.Caption, out rule))
         newRow[dc] = dr[rule]; // <- all the simple rules
     else if (dc.Caption.Equals("GF")) { // <- few specific rules
       ...
     }
   }

Answer 2

rules.Where(r => r.Key(s)).
    Select(r => r.Value(dr)).
    FirstOrDefault(); // Should do the trick.