ADO.NET Constraints

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Questions and Answers

What is the purpose of the DataRelation class?

To delete child DataRow objects when the parent DataRow object is deleted

To create a primary key constraint on the parent DataTable object

To create a unique constraint on the parent DataTable object and a foreign key constraint on the child DataTable object (correct)

To update child DataRow objects when the parent DataRow object is updated

What happens when a foreign key constraint is set to a DataColumn object that allows nulls?

The parent DataRow object is deleted when the child DataRow object is deleted

The child DataRow object can exist without a parent DataRow object (correct)

The child DataRow object cannot exist without a parent DataRow object

The child DataRow object is updated when the parent DataRow object is updated

What is the default setting for the DeleteRule property of the ForeignKeyConstraint?

Cascade (correct)

SetNull

SetDefault

None

What is the purpose of setting the DeleteRule property to Cascade?

To force the deletion of child DataRow objects when the parent DataRow object is deleted Signup and view all the answers

What is the purpose of verifying the AllowDBNull property of the DataColumn objects being used as foreign keys?

To ensure that the child DataRow object cannot exist without a parent DataRow object Signup and view all the answers

What is the purpose of setting the ChangeRule property?

To update child DataRow objects when the parent DataRow object is updated Signup and view all the answers

What is the result of creating a DataRelation object with a unique constraint on the parent DataTable object and a foreign key constraint on the child DataTable object?

The child DataRow object cannot exist without a parent DataRow object Signup and view all the answers

What is the purpose of the DataRelation class in terms of data integrity?

To ensure that a parent DataRow object exists for any child DataRow object Signup and view all the answers

What is the primary purpose of using a DataRelation object in ADO.NET?

To connect and coordinate data between multiple DataTables Signup and view all the answers

What is the benefit of using cascading deletes in a DataSet?

To prevent data inconsistencies when deleting related records Signup and view all the answers

How can you navigate through a DataTable in ADO.NET?

Enumerating the DataTable using a foreach loop Signup and view all the answers

What is the purpose of a primary key constraint in a DataTable?

To ensure data uniqueness and integrity Signup and view all the answers

What happens when you use the AcceptChanges method on a DataRow object?

The DataRow object's state is reset to Unchanged Signup and view all the answers

How can you create a foreign key constraint in a DataTable?

Using a DataRelation object Signup and view all the answers

What is the purpose of using a DataSet object in ADO.NET?

To coordinate work between multiple DataTables Signup and view all the answers

What happens when you use the RejectChanges method on a DataRow object?

The DataRow object's state is reset to its original state Signup and view all the answers

What is the default behavior of a ForeignKeyConstraint object when the parent DataRow object is deleted or its unique key is changed?

Deletes or updates the child DataRow objects Signup and view all the answers

What is the effect of setting the DeleteRule property of a ForeignKeyConstraint object to Rule.None?

Throws an InvalidConstraintException when the parent DataRow object is deleted or its unique key is changed Signup and view all the answers

What is the purpose of the Merge method in the DataSet class?

To combine data from multiple DataSet objects Signup and view all the answers

What type of exception is thrown when a parent DataRow object is deleted or its unique key is changed and the DeleteRule property is set to Rule.None?

InvalidConstraintException Signup and view all the answers

What is the result of setting the DeleteRule property of a ForeignKeyConstraint object to Rule.SetDefault?

The foreign key column(s) value is set to the default value of the DataColumn object(s) Signup and view all the answers

What is the purpose of using a ForeignKeyConstraint object?

To enforce data integrity in a DataSet Signup and view all the answers

What is the effect of setting the DeleteRule property of a ForeignKeyConstraint object to Rule.SetNull?

The foreign key column(s) value is set to DBNull Signup and view all the answers

What is the benefit of using the Merge method to combine data from multiple DataSet objects?

It allows for the combination of data from multiple sources Signup and view all the answers

Study Notes

ForeignKeyConstraint

Deletes or updates child DataRow objects when the parent DataRow object is deleted or its unique key is changed.
Default behavior is to cascade the changes.
Can be set to throw an InvalidConstraintException if the parent DataRow object is deleted or its unique key is changed.
Can be set to set the foreign key column(s) value to the default value of the DataColumn object(s) if the parent DataRow object is deleted or its unique key is changed.
Can be set to set the foreign key column(s) value to DBNull if the parent DataRow object is deleted or its unique key is changed.

Merge Method

Used to combine data from multiple DataSet objects.
Has several overloads to merge data from DataSet, DataTable, or DataRow objects.
Can be used to merge changes from one data set into another data set.

DataRelation

Provides a constructor that enables the creation of a unique constraint on the parent DataTable object and a foreign key constraint on the child DataTable object.
Ensures data integrity by ensuring that a parent DataRow object exists for any child DataRow object.
Can be created with or without constraints.

Cascade Deletes and Cascade Updates

Ensures that child DataRow objects cannot be added unless a valid parent DataRow object exists.
Can be set to delete child DataRow objects when the parent DataRow object is deleted.
Can be set to cascade changes to a unique key in the parent DataRow object to the child DataRow object's foreign key.

Constraints

Can be set to ensure data integrity.
Can be set to allow or disallow nulls in the DataColumn objects being used as foreign keys.

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Description

This quiz covers the different types of constraints in ADO.NET, including their behavior when the parent DataRow object is deleted or its unique key is changed.