vb.net 合并两个数据表的最佳方法
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Best way to merge two Datatables
提问by dr alialadin
I need to marge two datatables with condition. I have a datatable where the data comes from a local XML Database and another datatable where the data comes from a remote SQL Server.
我需要用条件对两个数据表进行边缘处理。我有一个数据表，其中数据来自本地 XML 数据库和另一个数据表，其中数据来自远程 SQL Server。
If any update made in the remote datatable I need to update/merge with the local datatable. Here is what I have so far:
如果在远程数据表中进行了任何更新，我需要更新/与本地数据表合并。这是我到目前为止所拥有的：
Public Sub MargeTwoTable()
Dim SQL As String = ""
Dim RemoteTable As New DataTable
Dim LocalTable As DataTable
Dim dal As New DalComon
Dim yy As Integer = 0
Dim UpdateDate As String
Dim TableName As String = "V_Book_Price"
LocalTable = LoadDataTable(TableName, True)
UpdateDate = LocalTable.Compute("MAX(update_date)", Nothing)
SQL = "select * from V_Book_Price where Update_Date > '" & UpdateDate & "'"
RemoteTable = dal.GetDataSetBySQL(SQL).Tables(0)
If RemoteTable.Rows.Count > 0 Then
For i = 0 To RemoteTable.Rows.Count - 1
Dim st As DataRow
Dim mm() As DataRow = LocalTable.Select("ID = '" & RemoteTable.Rows(i).Item("ID") & "'")
If mm.Length = 0 Then
st = LocalTable.NewRow
For yy = 0 To RemoteTable.Columns.Count - 1
st(yy) = RemoteTable.Rows(i)(yy)
Next
LocalTable.Rows.Add(st)
Else
st = mm(0)
For yy = 0 To RemoteTable.Columns.Count - 1
If IsDate(RemoteTable.Rows(i)(yy)) Then
st(yy) = CDate(RemoteTable.Rows(i)(yy)).ToString("s")
Else
st(yy) = RemoteTable.Rows(i)(yy)
End If
Next
mm = Nothing
End If
Next
End If
End Sub
In this code data comes from the remote database which updates a date getter then the local database . Both tables have "ID" as the primary key. The code is working well, but the problem is that when more than 1000 records are updated this function takes too long using loops.
在这段代码中，数据来自远程数据库，它更新日期获取器，然后是本地数据库。两个表都将“ID”作为主键。代码运行良好，但问题是当更新超过 1000 条记录时，此函数使用循环花费的时间太长。
回答by Steve
Not sure if can be applicable, but have you ever looked at the
DataTable.LoadDataRow()method?.
It seems a good candidate to substitute all of you code above.
不确定是否适用，但您是否看过
DataTable.LoadDataRow()方法？。
替换上面的所有代码似乎是一个不错的选择。
Your code could be simplified to these lines
您的代码可以简化为这些行
Dim row as DataRow
For Each row in RemoteTable.Rows
LocalTable.LoadDataRow(row.ItemArray, false)
Next
Another alternative could be the DataTable.Mergethat could cut your code to a single line
另一种选择可能是DataTable.Merge，它可以将您的代码切成一行
LocalTable.Merge(RemoteTable, False)
However, the real effectiveness of these two methods depends on the schema compatibility and from the presence of AutoNumber (identity) columns.
但是，这两种方法的真正有效性取决于模式兼容性和自动编号（标识）列的存在。
