向DataTable问题添加行

Question

Greetings everyone-

In my code below I'm trying to add a Row from an existing DataTable (dtResult) into a new DataTable (dtCopyResult) if email address does not match. So I guess my knowledge of ADO.NET is not up to par because whenever I try to run my below code, I get an "This Row already belongs to another table". Please let me know how I can fix this..

Many Thanks

 if (checkBox1.Checked)  
                    {

                        for (int i = dtResult.Rows.Count - 1; i >= 0; i--)  //dtResult is a DataTable
                        {
                            foreach (object email in emails)  //emails is an ArrayList of email addresses
                            {
                                if (email.ToString().ToUpper() != dtResult.Rows[i][3].ToString().ToUpper())
                                {
                                    dtCopyResult.Rows.Add(dtResult.Rows[i]);  //dtCopyResult is a new blank DataTable that I'm trying to add rows to
                                }
                            }

                        }

                    }

Answer 1

As the error message tells you, a DataRow belongs to a particular DataTable; you cannot just take it and add it to another one. What you can do is either

• create a new DataRow and fill it with the values from the old DataRow or

• use the DataTable.ImportRow method:

   dtCopyResult.ImportRow(dtResult.Rows[i]); 

Answer 2

您可以使用ImportRow函数，完整的示例在这里http://support.microsoft.com/kb/308909

Answer 3

One thing I noticed is that the new row will get added multiple times; once for each item in the emails collection. You either need to keep a local list of items already added or loop through dtCopyResult to make sure you have not already added the email.

List<string> alreadyAdded = new List<string>();

if (email.ToString().ToUpper() != dtResult.Rows[i][0].ToString().ToUpper() 
    && !alreadyAdded.Contains(email.ToString()))
{
    dtCopyResult.ImportRow(_dt1.Rows[i]);
    alreadyAdded.Add(email.ToString());
}

Answer 4

it means the adding row is belong to "dtResult" and DataRow is an "Object" that represent data. Not data itselfs. so in this case u try to add DataRow object that belong to another table which will error.

another way to do is copy everything to dtCopy and delete it if condition mismatch. Array is mainly to used to stored various type of object. In this case, if u gonna store only email u should use

List<string> emails = new List<string>();
emails.Add("test@example.com");

to enumerate rows for deleteing data

List<DataRow> removing = new List<DataRow>();
foreach(var row in table.AsEnumerable()) // or table.Rows
if(...condition)removing.Add(row);

foreach(var row in removing)table.Rows.Remove(row);

the reason to use 'removing' is if u loop through rows and removing it at the same time, means u change the enumerate which will cause error. becus .Net is not happy when u pull out something its looping.

Answer 5

Try replacing

 dtCopyResult.Rows.Add(dtResult.Rows[i]);

with

DataRow rowToBeCopied = dtCopyResult.NewRow();
//Copy the row values..
rowToBeCopied.X = dtResult.Rows[i].X;
//Copy the remaining row values
dtCopyResult.Rows.Add(rowToBeCopied);