Constraint Classe

Definição

public ref class Constraint abstract

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

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

public abstract class Constraint

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

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

type Constraint = class

Public MustInherit Class Constraint

Herança

Object

Constraint

Derivado

System.Data.ForeignKeyConstraint

System.Data.UniqueConstraint

Atributos

TypeConverterAttribute SerializableAttribute

Exemplos

O exemplo a seguir examina a coleção de restrições para um DataTable e determina se cada restrição é um UniqueConstraint ou um ForeignKeyConstraint. Em seguida, as propriedades da restrição são exibidas.

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

Comentários

Uma restrição é uma regra usada para manter a integridade dos dados no DataTable. Por exemplo, quando você exclui um valor usado em uma ou mais tabelas relacionadas, determina ForeignKeyConstraint se os valores nas tabelas relacionadas também são excluídos, definidos como valores nulos, definidos como valores padrão ou se nenhuma ação ocorre. Um UniqueConstraint, por outro lado, apenas garante que todos os valores em uma tabela específica sejam exclusivos. Para obter mais informações, consulte Restrições de DataTable.

Um construtor base Constraint não é usado. Restrições de chave primárias ou exclusivas são criadas usando o UniqueConstraint construtor e restrições de chave estrangeira são criadas usando o ForeignKeyConstraint construtor.

Acesso thread-safe

Esse tipo é seguro para operações de leitura multithreaded. Você deve sincronizar todas as operações de gravação.

Confira também

• ConstraintCollection
• Constraints
• ForeignKeyConstraint
• UniqueConstraint