Programming DAO: Data Definition Language - Access Database Design and Programming - page 238

Note that the difference between a primary key index and a unique values index is that a
primary key is not allowed to have NULL values.

15.5 Creating a Relation

Relations are created in DAO using the CreateRelation method. The syntax is:

Set RelationVar = DatabaseVar .CreateRelation _
([ RelName [, KeyTable [, ForeignTable [, Attributes ]]]])

where:

• RelName is the name of the new relation.
• KeyTable is the name of the referenced table in the relation (containing the key).
• ForeignTable is the name of the referencing table in the relation (containing the
foreign key).
• Attributes is a constant, whose values are shown in Table 15-2.

Table 15-2. Attributes for a Relation object

Constant Description

dbRelationUnique Relationship is one-to-one
d bRelationDontEnforce N o referential integrity
dbRelationInherited Relationship exists in a noncurrent database that contains the two attached
t ables
dbRelationUpdateCascade Cascading updates enabled
d bRelationDeleteCascade C ascading deletions enabled

15.5.1 Notes

All of the properties of a Relation object become read-only after the object is
appended to a Relations collection.

•

Field objects for the referenced and referencing tables must be appended to the
Fields collection prior to appending the Relation object to the Relations
collection.

•

Duplicate or invalid names will cause an error when the Append method is
invoked.

•

To remove a Relation object from a collection, use the Delete method for that
collection.

•

Example 15-4 illustrates the use of Relation objects. In this example, we will create a
new relation in the LIBRARY database. The first step is to create a new table, using
Microsoft Access. Call the table SALESREGIONS, and add two text fields: PubID and
SalesRegions . Then add a few rows shown in Table 15-3 to the table.