检查值是否存在或为空

Question

一个问题...我在下面的示例中有一个代码...我必须将一些值插入数据库..但直接从数据行..我不想使用变量。所以我的问题是，有没有办法检查数据行中的值是否存在或是否为空，如果该值不存在我必须插入空或如果它为空，只需插入空...

例子：

myQuery = " INSERT INTO AGR3PL_CS (IDOC_NUM, PSEG_NUM, SEG_NUM, COMP01, GLNO01, NAME01) " +
          " VALUES (" + Lidoc_num + ", '" +
                        PSEG_NUM + "','" +
                        SEG_NUM + "','" +
                        dr_art_custsuply["Id"] + "','" +
                        dr_art_custsuply["GLN"] + "','" +
                        dr_art_custsuply["Name"] + "')";

这是我不想用的方式……

if (!dr_art_custsuply.Table.Columns.Contains("GLN") || dr_art_custsuply["GLN"].ToString().Length <= 0)
{
    gln = "";
}
else
{
    gln = dr_art_custsuply["GLN"].ToString();
}

Answer 1

简单地做

Convert.ToString(dr_art_custsuply["GLN"])

如果它有值，那么将发送该值。否则为 null，因为 Convert.ToString() 处理 null。

注意：不要做.ToString()，因为它会在值为空时抛出异常。
阅读Difference between Convert.ToString() and .ToString()

Answer 2

1. 参数
2. DBNull.Value

例如（因为您使用的是 oracle）：

cmd.CommandText = @"
INSERT INTO AGR3PL_CS (IDOC_NUM, PSEG_NUM, SEG_NUM, COMP01, GLNO01, NAME01)
VALUES (:IDOC_NUM, :PSEG_NUM, :SEG_NUM, :COMP01, :GLNO01, :NAME01)";
cmd.Parameters.AddWithValue("IDOC_NUM", Lidoc_num);
cmd.Parameters.AddWithValue("PSEG_NUM", PSEG_NUM);
cmd.Parameters.AddWithValue("SEG_NUM", SEG_NUM);
cmd.Parameters.AddWithValue("COMP01", dr_art_custsuply["Id"] ?? DBNull.Value);
cmd.Parameters.AddWithValue("GLNO01", dr_art_custsuply["GLN"] ?? DBNull.Value);
cmd.Parameters.AddWithValue("NAME01", dr_art_custsuply["Name"] ?? DBNull.Value);
cmd.ExecuteNonQuery();

或者如果您需要通过“dapper”获得帮助（因为您提到参数数量是个问题）：

connection.Execute(@"
INSERT INTO AGR3PL_CS (IDOC_NUM, PSEG_NUM, SEG_NUM, COMP01, GLNO01, NAME01)
VALUES (:Lidoc_num, :PSEG_NUM, :SEG_NUM, :Comp, :Gln, :Name)",
    new { Lidoc_num, PSEG_NUM, SEG_NUM,
        Comp = (int?)dr_art_custsuply["Id"],
        Gln = (string)dr_art_custsuply["GLN"],
        Name = (string)dr_art_custsuply["Name"] });

Answer 3

永远不要在 SQL 中插入值，而是使用 parameters/Bind 变量：

using Oracle.DataAccess.Client; // <- In case of using Oracle 

...

String myQuery = 
 @"insert into AGR3PL_CS(
     IDOC_NUM, 
     PSEG_NUM, 
     SEG_NUM, 
     COMP01, 
     GLNO01, 
     NAME01)
   values (
     :PRM_IDOC_NUM, -- <- Assuming that you use Oracle; @PRM_IDOC_NUM for MS SQL
     :PRM_PSEG_NUM, 
     :PRM_SEG_NUM, 
     :PRM_COMP01, 
     :PRM_GLNO01, 
     "PRM_NAME01)"; 

  ....

  using(OracleCommand cmd = new OracleCommand()) {
    ...
    cmd.CommandText = myQuery;

    // For MS SQL use
    // cmd.Parameters.AddWithValue("@PRM_IDOC_NUM", Lidoc_num); 
    cmd.Parameters.Add(":PRM_IDOC_NUM", Lidoc_num);
    cmd.Parameters.Add(":PRM_PSEG_NUM", PSEG_NUM);
    cmd.Parameters.Add(":PRM_SEG_NUM", SEG_NUM);
    cmd.Parameters.Add(":PRM_COMP01", dr_art_custsuply["Id"]);
    cmd.Parameters.Add(":PRM_GLNO01", dr_art_custsuply["GLN"]);
    cmd.Parameters.Add(":PRM_NAME01", dr_art_custsuply["Name"]);

    cmd.ExecuteNonQuery();
  }

Answer 4

您可以这样做（并将其用于大多数预期的类型）：

var customerId = (CheckNull(dr_art_custsuply["Id"], String.Empty)).ToString();


public static object CheckNull(object value, object defaultValue)
{
     return ((value == null || value == DBNull.Value) ? defaultValue : value);
}

Answer 5

使用内联三元运算符：

 gln = (!dr_art_custsuply.Table.Columns.Contains("GLN") || dr_art_custsuply["GLN"].ToString().Length <= 0 ?  string.Empty : dr_art_custsuply["GLN"].ToString());

所以myQuery 变成：

myQuery = " INSERT INTO AGR3PL_CS (IDOC_NUM, PSEG_NUM, SEG_NUM, COMP01, GLNO01, NAME01) " +
          " VALUES (" + Lidoc_num + ", '" +
                        PSEG_NUM + "','" +
                        SEG_NUM + "','" +
                        dr_art_custsuply["Id"] + "','" +
                        (!dr_art_custsuply.Table.Columns.Contains("GLN") || dr_art_custsuply["GLN"].ToString().Length <= 0 ?  string.Empty : dr_art_custsuply["GLN"].ToString()) + "','" +
                        dr_art_custsuply["Name"] + "')";

编辑：回答您评论中的问题：

myQuery = " INSERT INTO AGR3PL_CS (IDOC_NUM, PSEG_NUM, SEG_NUM, COMP01, GLNO01, NAME01) " +
          " VALUES (" + Lidoc_num + ", '" +
                        PSEG_NUM + "','" +
                        SEG_NUM + "','" +
                        dr_art_custsuply["Id"] + "','" +
                        (!dr_art_custsuply.Table.Columns.Contains("GLN") || dr_art_custsuply["GLN"].ToString().Length <= 0 ? 0 : dr_art_custsuply["GLN"].ToString()) + "','" +
                        (!dr_art_custsuply.Table.Columns.Contains("Name") || dr_art_custsuply["Name"].ToString().Length <= 0 ? String.Empty : dr_art_custsuply["Name"].ToString()) + "')";