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ChildViews and Relations

  • Bài viết

If a relationship exists between tables in a DataSet, you can create a DataView containing rows from the related child table by using the CreateChildView method of the DataRowView for the rows in the parent table. For example, the following code displays Categories and their related Products in alphabetical order sorted by CategoryName and ProductName.

Dim catTable As DataTable = catDS.Tables("Categories")  
Dim prodTable As DataTable = catDS.Tables("Products")  
  
' Create a relation between the Categories and Products tables.  
Dim relation As DataRelation = catDS.Relations.Add("CatProdRel", _  
  catTable.Columns("CategoryID"), _  
  prodTable.Columns("CategoryID"))  
  
' Create DataViews for the Categories and Products tables.  
Dim catView As DataView = New DataView(catTable, "", _  
  "CategoryName", DataViewRowState.CurrentRows)  
Dim prodView As DataView  
  
' Iterate through the Categories table.  
Dim catDRV, prodDRV As DataRowView  
  
For Each catDRV In catView  
  Console.WriteLine(catDRV("CategoryName"))  
  
  ' Create a DataView of the child product records.  
  prodView = catDRV.CreateChildView(relation)  
  prodView.Sort = "ProductName"  
  
  For Each prodDRV In prodView  
    Console.WriteLine(vbTab & prodDRV("ProductName"))  
  Next  
Next  

DataTable catTable = catDS.Tables["Categories"];  
DataTable prodTable = catDS.Tables["Products"];  
  
// Create a relation between the Categories and Products tables.  
DataRelation relation = catDS.Relations.Add("CatProdRel",
  catTable.Columns["CategoryID"],  
                                                            prodTable.Columns["CategoryID"]);  
  
// Create DataViews for the Categories and Products tables.  
DataView catView = new DataView(catTable, "", "CategoryName",
  DataViewRowState.CurrentRows);  
DataView prodView;  
  
// Iterate through the Categories table.  
foreach (DataRowView catDRV in catView)  
{  
  Console.WriteLine(catDRV["CategoryName"]);  
  
  // Create a DataView of the child product records.  
  prodView = catDRV.CreateChildView(relation);  
  prodView.Sort = "ProductName";  
  
  foreach (DataRowView prodDRV in prodView)  
    Console.WriteLine("\t" + prodDRV["ProductName"]);  
}

See also