轻松玩转Typed DataSet, Part III
轻松玩转Typed DataSet, Part III
Written by: Rickie Lee
Dec. 10, 2004
本文继续前面《轻松玩转Typed DataSet, Part II》，这里演练在使用Typed DataSet过程中，如何有效地Debug程序中出现的错误。最常见的错误Exception应该是：
An unhandled exception of type 'System.Data.ConstraintException' occurred in system.data.dll
Additional information: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.
显然，通过VS.Net IDE显式的上述Exception信息，很难判断到底错误在什么地方。这里提供的一个有效的方法来Debug，尽快找到Bug的真正原因，并加以解决。
private void PrintAllErrs(DataSet myDataSet)
{
DataRow[] rowsInError;
foreach(DataTable myTable in myDataSet.Tables)
{
// Test if the table has errors. If not, skip it.
if(myTable.HasErrors)
{
// Get an array of all rows with errors.
rowsInError = myTable.GetErrors();
Console.WriteLine(myTable.TableName + " " + rowsInError.Length.ToString()
+ " " + rowsInError[0].RowError);
// Print the error of each column in each row.
/*for(int i = 0; i < rowsInError.Length; i++)
{
foreach(DataColumn myCol in myTable.Columns)
{
Console.WriteLine(myCol.ColumnName + " " +
rowsInError[i].GetColumnError(myCol));
}
// Clear the row errors
rowsInError[i].ClearErrors();
}*/
}
}
}
通过上面的PrintAllErrs()方法，明确输出错误的信息，其中注释的for语句根据时间情况来确定是否需要。
下面演示如何使用上述Code snippet，下面的代码与前面的post《轻松玩转Typed DataSet, Part II》相关，更详细的信息，请参考《轻松玩转Typed DataSet, Part II》：
AnnotationTypedDataset theOrderDS = new AnnotationTypedDataset();
try
{
string strSelectOrders = "Select top 5 * From Orders ";
strSelectOrders += "Select * From [Order Details]";
SqlHelper.FillDataset(connStr, CommandType.Text, strSelectOrders, theOrderDS, new string[] {"Orders", "OrderDetails"});
StringBuilder strResults = new StringBuilder();
foreach(AnnotationTypedDataset.Order theOrder in theOrderDS.Orders)
{
strResults.Append(theOrder.OrderID.ToString() + " "
+ theOrder.CustomerID.ToString() + " "
+ theOrder.EmployeeID.ToString() + Environment.NewLine);
strResults.Append("Order Details: ");
strResults.Append(theOrder.GetChildRows("OrdertoOrderDetails").Length.ToString() + " ");
strResults.Append(theOrder.GetOrderDetails().Length.ToString());
strResults.Append(Environment.NewLine);
}
txtResults.Text = strResults.ToString();
}
catch
{
PrintAllErrs(theOrderDS);
}
异常Exception输出结果：
OrderDetails 2141 ForeignKeyConstraint OrdertoOrderDetails requires the child key values (10253) to exist in the parent table.
包含有错误的table name，错误的Rows总数，并输出第1行错误的具体信息，如果要输出所有行的错误信息，则需要开发PrintAllErrs()方法的for循环。
通过上面输出的错误信息，可以很快发现是上面的SQL语句有问题，子表OrderDetails的key值在父表Orders不存在。
Any questions or errors, please leave comments below. Thanks.
References:
1. Rickie, 轻松玩转Typed DataSet, Part I
2. Rickie, 轻松玩转Typed DataSet, Part II
3. MSDN, DataTable.GetErrors Method, http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemDataDataTableClassGetErrorsTopic.asp
