Constraint Classe

Definizione

public ref class Constraint abstract

[System.ComponentModel.TypeConverter(typeof(System.Data.ConstraintConverter))]
public abstract class Constraint

public abstract class Constraint

[System.ComponentModel.TypeConverter(typeof(System.Data.ConstraintConverter))]
[System.Serializable]
public abstract class Constraint

[<System.ComponentModel.TypeConverter(typeof(System.Data.ConstraintConverter))>]
type Constraint = class

type Constraint = class

[<System.ComponentModel.TypeConverter(typeof(System.Data.ConstraintConverter))>]
[<System.Serializable>]
type Constraint = class

Public MustInherit Class Constraint

Ereditarietà

Object

Constraint

Derivato

System.Data.ForeignKeyConstraint

System.Data.UniqueConstraint

Attributi

TypeConverterAttribute SerializableAttribute

Esempio

Nell'esempio seguente viene esaminata la raccolta di vincoli per un DataTable oggetto e viene determinato se ogni vincolo è o UniqueConstraint .ForeignKeyConstraint Le proprietà del vincolo vengono quindi visualizzate.

private void GetConstraints(DataTable dataTable)
{
    Console.WriteLine();

    // Print the table's name.
    Console.WriteLine("TableName: " + dataTable.TableName);

    // Iterate through the collection and
    // print each name and type value.
    foreach(Constraint constraint in dataTable.Constraints )
    {
        Console.WriteLine("Constraint Name: "
            + constraint.ConstraintName);
        Console.WriteLine("Type: "
            + constraint.GetType().ToString());

        // If the constraint is a UniqueConstraint,
        // print its properties using a function below.
        if(constraint is UniqueConstraint)
        {
            PrintUniqueConstraintProperties(constraint);
        }
        // If the constraint is a ForeignKeyConstraint,
        // print its properties using a function below.
        if(constraint is ForeignKeyConstraint)
        {
            PrintForeignKeyConstraintProperties(constraint);
        }
    }
}

private void PrintUniqueConstraintProperties(
    Constraint constraint)
{
    UniqueConstraint uniqueConstraint;
    uniqueConstraint = (UniqueConstraint) constraint;

    // Get the Columns as an array.
    DataColumn[] columnArray;
    columnArray = uniqueConstraint.Columns;

    // Print each column's name.
    for(int i = 0;i<columnArray.Length ;i++)
    {
        Console.WriteLine("Column Name: "
            + columnArray[i].ColumnName);
    }
}

private void PrintForeignKeyConstraintProperties(
    Constraint constraint)
{
    ForeignKeyConstraint fkConstraint;
    fkConstraint = (ForeignKeyConstraint) constraint;

    // Get the Columns as an array.
    DataColumn[] columnArray;
    columnArray = fkConstraint.Columns;

    // Print each column's name.
    for(int i = 0;i<columnArray.Length ;i++)
    {
        Console.WriteLine("Column Name: "
            + columnArray[i].ColumnName);
    }
    Console.WriteLine();

    // Get the related columns and print each columns name.
    columnArray = fkConstraint.RelatedColumns ;
    for(int i = 0;i<columnArray.Length ;i++)
    {
        Console.WriteLine("Related Column Name: "
            + columnArray[i].ColumnName);
    }
    Console.WriteLine();
}

Private Sub GetConstraints(dataTable As DataTable)
    Console.WriteLine()

    ' Print the table's name.
    Console.WriteLine("TableName: " & dataTable.TableName)

    ' Iterate through the collection and print 
    ' each name and type value.
    Dim constraint As Constraint
    For Each constraint In  dataTable.Constraints
        Console.WriteLine("Constraint Name: " _
            & constraint.ConstraintName)
        Console.WriteLine("Type: " _
            & constraint.GetType().ToString())

        ' If the constraint is a UniqueConstraint, 
        ' print its properties using a function below.
        If TypeOf constraint Is UniqueConstraint Then
            PrintUniqueConstraintProperties(constraint)
        End If

        ' If the constraint is a ForeignKeyConstraint, 
        ' print its properties using a function below.
        If TypeOf constraint Is ForeignKeyConstraint Then
            PrintForeigKeyConstraintProperties(constraint)
        End If
    Next constraint
End Sub

Private Sub PrintUniqueConstraintProperties( _
    constraint As Constraint)

    Dim uniqueConstraint As UniqueConstraint
    uniqueConstraint = CType(constraint, UniqueConstraint)

    ' Get the Columns as an array.
    Dim columnArray() As DataColumn
    columnArray = uniqueConstraint.Columns

    ' Print each column's name.
    Dim i As Integer
    For i = 0 To columnArray.Length - 1
        Console.WriteLine("Column Name: " _
            & columnArray(i).ColumnName)
    Next i
End Sub

Private Sub PrintForeigKeyConstraintProperties( _
    constraint As Constraint)

    Dim fkConstraint As ForeignKeyConstraint
    fkConstraint = CType(constraint, ForeignKeyConstraint)
    
    ' Get the Columns as an array.
    Dim columnArray() As DataColumn
    columnArray = fkConstraint.Columns
    
    ' Print each column's name.
    Dim i As Integer
    For i = 0 To columnArray.Length - 1
        Console.WriteLine("Column Name: " _
            & columnArray(i).ColumnName)
    Next i
    Console.WriteLine()
    
    ' Get the related columns and print each columns name.
    columnArray = fkConstraint.RelatedColumns
    For i = 0 To columnArray.Length - 1
        Console.WriteLine("Related Column Name: " _
            & columnArray(i).ColumnName)
    Next i
    Console.WriteLine()
End Sub

Commenti

Un vincolo è una regola usata per mantenere l'integrità dei dati in DataTable. Ad esempio, quando si elimina un valore utilizzato in una o più tabelle correlate, un oggetto ForeignKeyConstraint determina se anche i valori nelle tabelle correlate vengono eliminati, impostati su valori Null, impostati su valori predefiniti o se non si verifica alcuna azione. Un UniqueConstraintoggetto , d'altra parte, garantisce solo che tutti i valori all'interno di una determinata tabella siano univoci. Per altre informazioni, vedere Vincoli DataTable.

Non viene utilizzato un costruttore di base Constraint . I vincoli di chiave primaria o univoca vengono creati usando il UniqueConstraint costruttore e i vincoli di chiave esterna vengono creati usando il ForeignKeyConstraint costruttore .

Costruttori

Proprietà

Metodi

Si applica a

Thread safety

Questo tipo è sicuro per le operazioni di lettura multithreading. È necessario sincronizzare tutte le operazioni di scrittura.

Vedi anche

• ConstraintCollection
• Constraints
• ForeignKeyConstraint
• UniqueConstraint