vb.net 检查 DataReader 中是否存在列的有效方法
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Efficient way to check if Columns exist in the DataReader
提问by user1263981
There are tables with over 50 columns, I am using following code to loop through the dataReader for column existence.
有超过 50 列的表，我使用以下代码循环遍历 dataReader 以获取列存在。
If HasColumn(reader, "EmpCode") Then obj.OwningOfficeID = CType(reader("EmpCode"), Int32)
Protected Function HasColumn(ByRef reader As SqlDataReader, ByVal columnName As String) As Boolean
For i As Integer = 0 To reader.FieldCount - 1
If reader.GetName(i).Equals(columnName) Then
Return Not IsDBNull(reader(columnName))
End If
Next
Return False
End Function
I am wondering if there is any better way of checking the columns in the DataReader instead of looping through the DataReader each time i bind the object property?
我想知道是否有更好的方法来检查 DataReader 中的列而不是每次绑定对象属性时循环遍历 DataReader？
回答by Rajesh Subramanian
SqlDataReader.GetSchemaTableMethod will give the DataTable of the executed query, from there you can get all the columns
SqlDataReader.GetSchemaTable方法将给出执行查询的数据表，从那里你可以得到所有的列
Returns a DataTable that describes the column metadata.
MSDN http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getschematable.aspx
MSDN http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getschematable.aspx
回答by th1rdey3
currently I am using this extension method for this purpose
目前我正在为此目的使用此扩展方法
public static bool TryGetOrdinal(this IDataRecord dr, string column, out int ordinal)
{
try
{
ordinal = dr.GetOrdinal(column);
}
catch(Exception ex)
{
ordinal = -1; //Just setting a value that GetOrdinal doesn't return
return false;
}
return true;
}
so you use it as follows
所以你使用它如下
int ordinal = 0;
if(dr.TryGetOrdinal("column",out ordinal))
string val = dr.GetValue(ordinal).ToString();
My VB is not so good. Sorry couldn't convert it to VB for you. But I think you get the basic idea and can recode it in VB.
我的VB不太好。抱歉，无法为您将其转换为 VB。但我认为您已经掌握了基本思想，并且可以在 VB 中对其进行重新编码。
