如何检查数据读取器中是否存在列 [英] How to check if a column exists in a datareader

问题描述

我想在尝试读取数据列之前检查其是否存在列
我尝试下面的一些代码

I want to check if a column exists in the datareader before attempting to read it
i try some of code below

string ColumnValue;

if (dr["ColumnName"] != null)
      ColumnValue = dr["ColumnName"].ToString();

if (dr.GetSchemaTable().Columns["ColumnName"] != null)
      ColumnValue = dr["ColumnName"].ToString();

if (dr.GetSchemaTable().Columns.IndexOf("ColumnName")> 0)
      ColumnValue = dr["ColumnName"].ToString();

但它不起作用.关于这个的任何想法.
谢谢

but its not work. any idea about this.
Thanks

推荐答案

循环将为您解决问题.
遍历所有列的名称，并检查您的列是否存在.

looping will give u a solution of problem.
loop through the all columns name and check if your column is exist or not.

for (int i=0; i < dr.FieldCount; i++)
 {
            
         if (dr.GetName(i).Equals(columnName,StringComparison.InvariantCultureIgnoreCase))
          return true;
 }
return false; 

引用该线程

http://stackoverflow.com/questions/373230/check-for- column-name-in-a-sqldatareader-object [ ^ ]

Refer this thread

http://stackoverflow.com/questions/373230/check-for-column-name-in-a-sqldatareader-object[^]

我坚持使用GetSchemaTable()方法，如MSDN文档所述:

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getschematable.aspx [ ^ ]

样本中可能有一两个错字:

I''d stick with the GetSchemaTable() method as the MSDN documentation explains:

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getschematable.aspx[^]

maybe there''s a typo or two in your sample:

string ColumnName;

if (dr[ColumnName] != null)
      ColumnName = dr[ColumnName].ToString();

if (dr.GetSchemaTable().Columns[ColumnName] != null)
      ColumnName = dr[ColumnName].ToString();

if (dr.GetSchemaTable().Columns.IndexOf(ColumnName)> 0)
      ColumnName = dr[ColumnName].ToString();

尝试删除ColumnName周围的引号，以便您使用的是ColumnName的值，而不是文字"ColumnName".

try removing the quotes around ColumnName so you''re using the value of ColumnName and not the literal "ColumnName".

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