Constraint 类
定义
重要
一些信息与预发行产品相关,相应产品在发行之前可能会进行重大修改。 对于此处提供的信息,Microsoft 不作任何明示或暗示的担保。
表示可在一个或多个 DataColumn 对象上强制执行的约束。
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
- 继承
-
Constraint
- 派生
- 属性
示例
以下示例检查 的约束 DataTable 集合,并确定每个约束是 还是 UniqueConstraintForeignKeyConstraint。 然后显示约束的属性。
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
注解
约束是用于维护 中数据完整性的规则 DataTable。 例如,删除在一个或多个相关表中使用的值时, ForeignKeyConstraint 将确定相关表中的值是否也被删除、设置为 null 值、设置为默认值,或者是否不执行任何操作。 另一 UniqueConstraint方面,只需确保特定表中的所有值都是唯一的。 有关详细信息,请参阅DataTable 约束。
不使用基 Constraint 构造函数。 主键或唯一键约束是使用 UniqueConstraint 构造函数创建的,外键约束是使用 ForeignKeyConstraint 构造函数创建的。
构造函数
Constraint() |
初始化 Constraint 类的新实例。 |
属性
_DataSet |
获取此约束所属的 DataSet。 |
ConstraintName |
ConstraintCollection 中的约束的名称。 |
ExtendedProperties |
获取用户定义的约束属性的集合。 |
Table |
获取向其应用约束的 DataTable。 |
方法
CheckStateForProperty() |
获取此约束所属的 DataSet。 |
Equals(Object) |
确定指定对象是否等于当前对象。 (继承自 Object) |
GetHashCode() |
作为默认哈希函数。 (继承自 Object) |
GetType() |
获取当前实例的 Type。 (继承自 Object) |
MemberwiseClone() |
创建当前 Object 的浅表副本。 (继承自 Object) |
SetDataSet(DataSet) |
设置约束的 DataSet。 |
ToString() |
获取 ConstraintName(如果存在)作为字符串。 |
适用于
线程安全性
此类型对于多线程读取操作是安全的。 必须同步所有写入操作。