Constraint 類別

定義

命名空間:

System.Data

組件:

System.Data.dll

表示可以在一或多個 DataColumn 對象上強制執行的條件約束。

public ref class Constraint abstract

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

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

Public MustInherit Class Constraint

繼承

Object

Constraint

衍生

System.Data.ForeignKeyConstraint

System.Data.UniqueConstraint

屬性

TypeConverterAttribute

範例

以下範例檢視 a DataTable 的限制集合，並判定每個限制是 a UniqueConstraint 還是 ForeignKeyConstraint。 然後顯示約束的性質。

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

備註

約束是一種用來維持資料 DataTable完整性的規則。 例如，當你刪除一個或多個相關資料表中的值時，a ForeignKeyConstraint 會判斷相關資料表中的值是否也被刪除、設為空值、設為預設值，或是否不發生任何動作。 而 A UniqueConstraint則確保特定表格中的所有值都是唯一的。 如需詳細資訊，請參閱 DataTable 條件約束。

不使用基礎 Constraint 建構器。 主要或唯一鍵約束是透過建 UniqueConstraint 構子建立的，外鍵限制則是透過建 ForeignKeyConstraint 構子建立。

建構函式

名稱	Description
Constraint()	初始化 Constraint 類別的新執行個體。

屬性

名稱	Description
_DataSet	取得這個條件約束所屬 DataSet。
ConstraintName	ConstraintCollection中的條件約束名稱。
ExtendedProperties	取得使用者定義條件約束屬性的集合。
Table	取得約束適用的 。DataTable

方法

名稱	Description
CheckStateForProperty()	取得這個條件約束所屬 DataSet。
Equals(Object)	判斷指定的 物件是否等於目前的物件。 (繼承來源 Object)
GetHashCode()	做為預設雜湊函式。 (繼承來源 Object)
GetType()	取得目前實例的 Type。 (繼承來源 Object)
MemberwiseClone()	建立目前 Object的淺層複本。 (繼承來源 Object)
SetDataSet(DataSet)	設定條件約束的 DataSet。
ToString()	取得 ConstraintName，如果有字串，則為 。

執行緒安全性

此類型適合多執行緒讀取操作。 您必須同步處理任何寫入作業。

另請參閱

• ConstraintCollection
• Constraints
• ForeignKeyConstraint
• UniqueConstraint