Lookup relationship options

When you create a lookup field on an object, you can choose whether the lookup field is required or optional. If it is set as optional, you can choose one of the following three actions to take place if the lookup record is deleted:

• Clear the value of this field:

  This is a default option and is a good choice when the field does not have to contain a value from the associated lookup record.

• Don't allow deletion of the lookup record that's part of a lookup relationship

  This option prevents the lookup record from being deleted and is a good choice for restricting deletions if you have dependencies, such as workflow rules, based on the lookup relationship.

• Delete this record also

  This option works similar to the master-detail relationship and deletes the record whenever the lookup record is deleted. However, such a deletion on a lookup relationship is known as a cascade-delete and bypasses security and sharing settings. As a result, users can delete records when the...