Example one-to-one

The rest of the topics in this section use the following business example.

Suppose the insurer had a regulatory requirement to have a set of activities periodically reviewed by the insurer's legal team. There are several fields needed to track this legal review, but they are applicable to only about 5% of all activities.

To improve database performance, the insurer opts to store this information in an ActivityLegalInfo_Ext entity and define it as a one-to-one with Activity.

• The Activity entity is the parent. Each activity can be associated with up to one ActivityLegalInfo_Ext.
• ActivityLegalInfo_Ext is the child. Each instance must be associated with exactly one Activity.

To implement this, the following has been added to the data model:

• Activity entity
  • ActivityLegalInfo_Ext
    • one-to-one
    • fkentity: ActivityLegalInfo_Ext
    • nullok: true
• ActivityLegalInfo_Ext entity
  • LegalCaseNumber
    • varchar with size 30
  • LegalReviewDate
    • datetime
  • Activity
    • foreign key
    • fkentity: Activity
    • nullok: false

Note the following:

• On Activity, the ActivityLegalInfo_Ext field has nullok set to true. This is because some Activity instances will have an associated ActivityLegalInfo_Ext, but most will not.
• On ActivityLegalInfo_Ext, the Activity field has nullok set to false. This is because every ActivityLegalInfo_Ext must be associated to an Activity.

For a complete list of all code used to build this example, see Complete code sample for one-to-ones.