The ForeignKeyConstraint Class

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The ForeignKeyConstraint Class You use an object of the ForeignKeyConstraint class to represent a foreign key constraint between two DataTable objects.

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Nội dung Text: The ForeignKeyConstraint Class

The ForeignKeyConstraint Class You use an object of the ForeignKeyConstraint class to represent a foreign key constraint between two DataTable objects. This ensures that each DataRow in your child DataTable has a matching DataRow in your parent DataTable. The ForeignKeyConstraint class is derived from the System.Data.Constraint class. Table 12.2 shows the ForeignKeyConstraint properties. Table 12.2: ForeignKeyConstraint PROPERTIES PROPERTY TYPE DESCRIPTION AcceptRejectRule AcceptRejectRule Gets or sets the AcceptRejectRule that indicates the action that is to take place when the AcceptChanges() method of the DataTable is called. The members of the System.Data.AcceptRejectRule enumeration are • Cascade, which indicates that the changes to the DataRow objects in the parent DataTable are also made in the child DataTable. • None, which indicates that no action takes place. The default is None. Columns DataColumn[] Gets the array of DataColumn objects from the child DataTable. ConstraintName string Gets the name of the UniqueConstraint object. DeleteRule Rule Gets or sets the Rule that indicates the action that is to take place when a DataRow in the parent DataTable is deleted. The members of the System.Data.Rule enumeration are • Cascade, which indicates that the delete or update to the DataRow objects in the parent DataTable is also made in the child DataTable.
Table 12.2: ForeignKeyConstraint PROPERTIES PROPERTY TYPE DESCRIPTION • None, which indicates that no action takes place. • SetDefault, which indicates that the DataColumn values in the child DataTable are to be set to the value in the DefaultValue property of the DataColumn. • SetNull, which indicates that the DataColumn values in the child DataTable are to be set to DBNull. The default is Cascade. ExtendedProperties PropertyCollection Gets the PropertyCollection object that you can use to store strings of additional information. RelatedColumns DataColumn[] Gets the array of DataColumn objects in the parent DataTable for the UniqueConstraint. RelatedTable DataTable Gets the parent DataTable for the UniqueConstraint. Table DataTable Gets the child DataTable to which the UniqueConstraint belongs. UpdateRule Rule Gets or sets the Rule that indicates the action that is to take place when a DataRow in the parent DataTable is updated. See the DeleteRule property for the members of the Rule enumeration. The default is Cascade.