请考虑以下情况：
使用.NET的DataSet.Merge(DataSet)方法，我们可以将B应用到A，创建一个新的DataSetC，即C = A.Merge(B)。
DataSet.Merge(DataSet) Merge 方法的问题在于，对于在 B 中标记为已删除的任何行 r，r 将在 C 中被标记为已修改。同时，很明显，C 中的 r 也应标记为已删除。
一个可行但我觉得没有吸引力的解决方案是手动枚举 B 中所有已删除的行，并使用它们的标识符在 C 中找到相同的行，然后将 C 中该行的 RowState 也更改为 Deleted。
上述问题的正确解决方案是什么？
【问题讨论】：
我一直在玩数据集，并想出了下面的演示代码（基于MSDN）来测试您提出的一些问题。 （.net框架4.0 VS2010）
我发现合并是无效的，所以在查看您的问题时，我们有 A.Merge(B) 并且 A 与 B 合并。
正常合并（没有 preserveChanges 标志）使 B 领先，因此当 B 中删除某些内容并且它存在于 A 中时，它也将在新 A 中删除。如果我正确阅读了您的问题，这就是您想要的行为. （测试输出 A）
如果您将 preservechanges 标志设置为 True，那么奇怪的事情就会开始发生，例如，已删除的标志将在新 A 中被修改。（测试输出 B）
如果您将 preservechnages 标志设置为 true，请将其设置为 false。据我所知，默认行为是您想要的，而您不是您所看到的。我怀疑还有其他问题，希望这可以帮助您朝着正确的方向前进
private static void DemonstrateMergeTable()
{
// Create a DataSet with one table, two columns, and data.
DataSet originalDataSet = new DataSet("dataSet");
DataSet mergeDataSet = new DataSet("mergeSet");
DataTable originalTable = CreateItemsTable(originalDataSet);
DataTable mergeTable = CreateTableToMergeWith(originalTable, mergeDataSet);
CreateTestSets(originalTable, mergeTable);
PrintValues(originalDataSet, "Original values");
PrintValues(mergeDataSet, "Table to merge with");
// Merge the table into the DataSet
Console.WriteLine("Merging");
//originalDataSet.Merge(mergeTable,false,MissingSchemaAction.Add);
//originalDataSet.Merge(mergeTable,true, MissingSchemaAction.Add);
originalDataSet.Merge(mergeTable);
PrintValues(originalDataSet, "Merged With table.");
}
private static void CreateTestSets(DataTable originalTable, DataTable mergeTable)
{
// a new row to the mergetable, no matching row in the original
mergeTable.Rows.Add(new Object[] { 30, 0 });
//deletedRow in original, added row in mergetable
originalTable.Rows[0].Delete(); //id = 0
mergeTable.Rows.Add(new Object[] { 0, 100 });
//deletedRow in mergeset, corresponding row in original
mergeTable.Rows[0].Delete(); //id = 5
//deletedRow in original, corrosponding row in merging
originalTable.Rows[6].Delete();
}
private static DataTable CreateItemsTable(DataSet dataSet)
{
DataTable table = new DataTable("Items");
// Add columns
DataColumn c1 = new DataColumn("id",
Type.GetType("System.Int32"), "");
DataColumn c2 = new DataColumn("Item",
Type.GetType("System.Int32"), "");
table.Columns.Add(c1);
table.Columns.Add(c2);
// DataColumn array to set primary key.
DataColumn[] keyCol = new DataColumn[1];
// Set primary key column.
keyCol[0] = c1;
table.PrimaryKey = keyCol;
// Add rows.
for (int i = 0; i < 10; i++)
{
DataRow row = table.NewRow();
row["id"] = i;
row["Item"] = i;
table.Rows.Add(row);
}
// Add table to the DataSet
dataSet.Tables.Add(table);
// Accept changes.
dataSet.AcceptChanges();
return table;
}
private static DataTable CreateTableToMergeWith(DataTable table, DataSet mergeSet)
{
DataTable t2 = table.Clone();
// Add rows.
for (int i = 5; i < 15; i++)
{
DataRow row = t2.NewRow();
row["id"] = i;
row["Item"] = i;
t2.Rows.Add(row);
}
mergeSet.Tables.Add(t2);
t2.AcceptChanges();
return t2;
}
private static void PrintValues(DataSet dataSet, string label)
{
Console.WriteLine("\n" + label);
foreach (DataTable table in dataSet.Tables)
{
PrintTable(table);
}
}
private static void PrintTable(DataTable table)
{
Console.WriteLine("TableName: " + table.TableName);
foreach (DataRow row in table.Rows)
{
DataRowState dataRowState = row.RowState;
foreach (DataColumn column in table.Columns)
{
string columnName = column.ColumnName;
Object o = dataRowState != DataRowState.Deleted ? row[column] : row[column, DataRowVersion.Original];
Console.Write("\t {0} \t:{1}",columnName, o);
}
Console.Write("\t ({0})", dataRowState);
Console.WriteLine();
}
}
TestOutput A (preservechanges = false)
Original values
TableName: Items
id :0 Item :0 (Deleted)
id :1 Item :1 (Unchanged)
id :2 Item :2 (Unchanged)
id :3 Item :3 (Unchanged)
id :4 Item :4 (Unchanged)
id :5 Item :5 (Unchanged)
id :6 Item :6 (Deleted)
id :7 Item :7 (Unchanged)
id :8 Item :8 (Unchanged)
id :9 Item :9 (Unchanged)
Table to merge with
TableName: Items
id :5 Item :5 (Deleted)
id :6 Item :6 (Unchanged)
id :7 Item :7 (Unchanged)
id :8 Item :8 (Unchanged)
id :9 Item :9 (Unchanged)
id :10 Item :10 (Unchanged)
id :11 Item :11 (Unchanged)
id :12 Item :12 (Unchanged)
id :13 Item :13 (Unchanged)
id :14 Item :14 (Unchanged)
id :30 Item :0 (Added)
id :0 Item :100 (Added)
Merging
Merged With table.
TableName: Items
id :0 Item :100 (Modified)
id :1 Item :1 (Unchanged)
id :2 Item :2 (Unchanged)
id :3 Item :3 (Unchanged)
id :4 Item :4 (Unchanged)
id :5 Item :5 (Deleted)
id :6 Item :6 (Modified)
id :7 Item :7 (Unchanged)
id :8 Item :8 (Unchanged)
id :9 Item :9 (Unchanged)
id :10 Item :10 (Unchanged)
id :11 Item :11 (Unchanged)
id :12 Item :12 (Unchanged)
id :13 Item :13 (Unchanged)
id :14 Item :14 (Unchanged)
id :30 Item :0 (Added)
测试输出 B（preservechanges 为 true）
Original values
TableName: Items
id :0 Item :0 (Deleted)
id :1 Item :1 (Unchanged)
id :2 Item :2 (Unchanged)
id :3 Item :3 (Unchanged)
id :4 Item :4 (Unchanged)
id :5 Item :5 (Unchanged)
id :6 Item :6 (Deleted)
id :7 Item :7 (Unchanged)
id :8 Item :8 (Unchanged)
id :9 Item :9 (Unchanged)
Table to merge with
TableName: Items
id :5 Item :5 (Deleted)
id :6 Item :6 (Unchanged)
id :7 Item :7 (Unchanged)
id :8 Item :8 (Unchanged)
id :9 Item :9 (Unchanged)
id :10 Item :10 (Unchanged)
id :11 Item :11 (Unchanged)
id :12 Item :12 (Unchanged)
id :13 Item :13 (Unchanged)
id :14 Item :14 (Unchanged)
id :30 Item :0 (Added)
id :0 Item :100 (Added)
Merging
Merged With table.
TableName: Items
id :0 Item :0 (Deleted)
id :1 Item :1 (Unchanged)
id :2 Item :2 (Unchanged)
id :3 Item :3 (Unchanged)
id :4 Item :4 (Unchanged)
id :5 Item :5 (Modified)
id :6 Item :6 (Deleted)
id :7 Item :7 (Modified)
id :8 Item :8 (Modified)
id :9 Item :9 (Modified)
id :10 Item :10 (Unchanged)
id :11 Item :11 (Unchanged)
id :12 Item :12 (Unchanged)
id :13 Item :13 (Unchanged)
id :14 Item :14 (Unchanged)
id :30 Item :0 (Added)
【讨论】：