Question

我的List<String>名为record，其最大Count为102.我需要提取50个元素并将其添加为查询参数。但是，所有50可能都不存在，如果没有，那么我需要将参数添加为DBNull.Value。以下工作，但有没有比检查每次索引是否存在更好的方法？

List<String> record = new List<String>(myRecord.ToString().Split(new string[] { "^" }, StringSplitOptions.None));

cmd.CommandText = "INSERT INTO myTable ([Field1], [Field3], [Field7], [Field9]"
+ ") VALUES ("
+ "@p1, @p2, @p3, @p4)"

if (record.ElementAtOrDefault(1) != null)
{
    cmd.Parameters.AddWithValue("@p1", record[1]);
}
else
{
    cmd.Parameters.AddWithValue("@p1", DBNull.Value);
}

if (record.ElementAtOrDefault(3) != null)
{
    cmd.Parameters.AddWithValue("@p2", record[3]);
}
else
{
    cmd.Parameters.AddWithValue("@p2", DBNull.Value);
}

if (record.ElementAtOrDefault(7) != null)
{
    cmd.Parameters.AddWithValue("@p3", record[7);
}
else
{
    cmd.Parameters.AddWithValue("@p3", DBNull.Value);
}

if (record.ElementAtOrDefault(9) != null)
{
    cmd.Parameters.AddWithValue("@p4", record[9]);
}
else
{
    cmd.Parameters.AddWithValue("@p4", DBNull.Value);
}

....
....repeat this for @p5 thru @p50
....

cmd.ExecuteNonQuery();

cmd.Parameters.Clear();

工作解决方案如下：

var indexes = new List<int> { 1, 2, 4, 5, 10, 19, 20, 21, 22, 23, 24, 25, 26, 27, 32, 33, 35, 36, 38, 39, 44, 45, 46, 49, 51, 52, 53, 54, 55, 56, 57, 58, 62, 64, 65, 66, 67, 68, 69, 70, 71, 72, 79, 80, 81, 82, 83 };

cmd.CommandText = "INSERT INTO myTable ([Field1], [Field3], [Field7], [Field9]"
+ ") VALUES ("
+ "@p1, @p2, @p3, @p4)"    

List<String> record = new List<String>(myRecord.ToString().Split(new string[] { "^" }, StringSplitOptions.None));

var records = record.Where((item, index) => indexes.Contains(index)).ToList();

for (int i = 0; i < 5; i++)
{
    string paramName = "@p" + (i);

    if (i <= records.Count-1)      //index starts with a 0 
    {
        cmd.Parameters.AddWithValue(paramName, (object)records[(i)] ?? DBNull.Value);
    }
    else
    {
        cmd.Parameters.AddWithValue(paramName, DBNull.Value);
    }
}

cmd.ExecuteNonQuery();
cmd.Parameters.Clear();

Answer 1

如果您按索引访问元素，那么您可以将索引存储到List：

var indexes = new List<int> { 1, 3, 7, 9 ... };

然后得到你的元素：

var records = record.Where((item,index) => indexes.Contains(index)).ToList();

然后使用for循环（而不是if语句）

for(int i=1; i<records.Count; i++)
{  
   string paramName = "@p" + i;
   cmd.Parameters.AddWithValue(paramName, records[i] ?? DBNull.Value);
}

Answer 2

完全没有经过测试，可能包含错误/错别字，但一般来说，我会这样做：

void ParseMyList(string[] myRecord)
{
    List<String> record = new List<String>(myRecord.ToString().Split(new string[] { "^" }, StringSplitOptions.None));
    Dictionary<int, string> paramLookup = new Dictionary<int, string>();

    paramLookup.Add(1, "@p1");
    paramLookup.Add(3, "@p2");
    paramLookup.Add(7, "@p3");
    paramLookup.Add(9, "@p4");
    /*
    ....
    ....repeat this for @p5 thru @p50
    ....
    */

    cmd.CommandText = "INSERT INTO myTable ([Field1], [Field3], [Field7], [Field9]"
        + ") VALUES ("
        + "@p1, @p2, @p3, @p4)"

    foreach (KeyValuePair<int, string> entry in paramLookup)
    {
        if (record.ElementAtOrDefault(entry.Value))
        {
            cmd.Parameters.AddWithValue(entry.Value, record[entry.Key]);
        }
        else
        {
            cmd.Parameters.AddWithValue(entry.Value, DBNull.Value);
        }
    }

    cmd.ExecuteNonQuery();

    cmd.Parameters.Clear();
}

反复检查列表以查看索引是否存在？

2 个答案: