UniqueConstraint Class
.NET Framework 4
Represents a restriction on a set of columns in which all values must be unique.
Namespace:
System.Data
Assembly: System.Data (in System.Data.dll)
The UniqueConstraint type exposes the following members.
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UniqueConstraint(DataColumn) | Initializes a new instance of the UniqueConstraint class with the specified DataColumn. |
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UniqueConstraint(DataColumn[]) | Initializes a new instance of the UniqueConstraint class with the given array of DataColumn objects. |
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UniqueConstraint(DataColumn, Boolean) | Initializes a new instance of the UniqueConstraint class with the DataColumn to constrain, and a value specifying whether the constraint is a primary key. |
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UniqueConstraint(DataColumn[], Boolean) | Initializes a new instance of the UniqueConstraint class with an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key. |
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UniqueConstraint(String, DataColumn) | Initializes a new instance of the UniqueConstraint class with the specified name and DataColumn. |
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UniqueConstraint(String, DataColumn[]) | Initializes a new instance of the UniqueConstraint class with the specified name and array of DataColumn objects. |
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UniqueConstraint(String, DataColumn, Boolean) | Initializes a new instance of the UniqueConstraint class with the specified name, the DataColumn to constrain, and a value specifying whether the constraint is a primary key. |
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UniqueConstraint(String, DataColumn[], Boolean) | Initializes a new instance of the UniqueConstraint class with the specified name, an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key. |
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UniqueConstraint(String, String[], Boolean) | Initializes a new instance of the UniqueConstraint class with the specified name, an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key. |
| Name | Description | |
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_DataSet | Infrastructure. Gets the DataSet to which this constraint belongs. (Inherited from Constraint.) |
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Columns | Gets the array of columns that this constraint affects. |
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ConstraintName | The name of a constraint in the ConstraintCollection. (Inherited from Constraint.) |
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ExtendedProperties | Gets the collection of user-defined constraint properties. (Inherited from Constraint.) |
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IsPrimaryKey | Gets a value indicating whether or not the constraint is on a primary key. |
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Table | Gets the table to which this constraint belongs. (Overrides Constraint.Table.) |
| Name | Description | |
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CheckStateForProperty | Infrastructure. Gets the DataSet to which this constraint belongs. (Inherited from Constraint.) |
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Equals | Compares this constraint to a second to determine if both are identical. (Overrides Object.Equals(Object).) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
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GetHashCode | Gets the hash code of this instance of the UniqueConstraint object. (Overrides Object.GetHashCode().) |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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SetDataSet | Sets the constraint's DataSet. (Inherited from Constraint.) |
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ToString | Gets the ConstraintName, if there is one, as a string. (Inherited from Constraint.) |
The UniqueConstraint is enforced on a single column (or columns) to ensure that a primary key value is unique.
Constraints are not enforced unless the EnforceConstraints property is set to true.
When the a DataSet is merged with a second DataSet, constraints are not enforced until all merges are completed.
The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true.
Public Sub CreateDataTable() Dim dataTable As DataTable = New DataTable dataTable.Columns.Add("CustomerID", Type.GetType("System.String")) dataTable.Columns.Add("CompanyName", Type.GetType("System.String")) Dim uniqueConstraint As UniqueConstraint = _ New UniqueConstraint("CustConstraint", _ New DataColumn() {dataTable.Columns("CustomerID"), _ dataTable.Columns("CompanyName")}) dataTable.Constraints.Add(uniqueConstraint) End Sub
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
