You can use this option to generate a dataset that is slightly more efficient and that contains fewer methods than one with the related-records capability.
When you create a DataRelation object, you have the option of specifying that the relation be used only to enforce constraints-that is, it will not also be used to access related records. With this setting, child records can contain references to invalid parent records.įor more information about updates in dataset tables, see Save data back to the database. No change is made to related child records. The foreign key in the related child records is set to its default value (as established by the column's DefaultValue property). Note: Using this rule can result in invalid data in the child table. With this setting, child records can be left as "orphans"-that is, they have no relationship to parent records. The change (update or delete) made to the parent record is also made in related records in the child table.Ĭhild records are not deleted, but the foreign key in the child records is set to DBNull. The rules that you can make are specified in the Rule enumeration and are listed in the following table.
Referential integrity rulesĪs part of the foreign-key constraint, you can specify referential integrity rules that are applied at three points: For information on suspending constraints in a dataset, see Turn off constraints while filling a dataset. If you create a foreign-key constraint by using the DataRelation object, instances of the ForeignKe圜onstraint class are added to the DataRelation object's ChildKe圜onstraint property.Ī unique constraint is implemented either by simply setting the Unique property of a data column to true or by adding an instance of the UniqueConstraint class to the DataRelation object's ParentKe圜onstraint property. DataRelation objects and constraintsĪ DataRelation object is also used to create and enforce the following constraints:Ī unique constraint, which guarantees that a column in the table contains no duplicates.Ī foreign-key constraint, which can be used to maintain referential integrity between a parent and child table in a dataset.Ĭonstraints that you specify in a DataRelation object are implemented by automatically creating appropriate objects or setting properties. Instead, the DataRelation tracks the relationship between tables and keeps parent and child records in sync. When you use a DataRelation object, no new recordset is created. In a true join, records are taken from parent and child tables and put into a single, flat recordset. It is important to understand the difference between a true join and the function of a DataRelation object. It can enforce constraints for referential integrity, such as deleting related child records when you delete a parent record.
It provides child records if you are in a parent record ( GetChildRows) and a parent record if you are working with a child record ( GetParentRow). It can make available the records related to a record you are working with. The DataRelation object performs two functions: Adding related tables to datasets by using the Data Source Configuration Wizard, or the Dataset Designer, creates and configures the DataRelation object for you.
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Applies to: Visual Studio Visual Studio for Mac Visual Studio Codeĭatasets that contain related data tables use DataRelation objects to represent a parent/child relationship between the tables and to return related records from one another.
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