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Oggetti ChildView e relazioni

  • Articolo

Se esiste una relazione tra le tabelle di un tipo DataSet, è possibile creare un tipo DataView contenente le righe della tabella figlio correlata usando il metodo CreateChildView di DataRowView per le righe della tabella padre. Il codice seguente, ad esempio, visualizza le tabelle Categories e le relative tabelle Products in ordine alfabetico per CategoryName e 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"]);  
}

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