What is the difference between a
required lookup filter and
optional lookup filter.
I found those three concepts in many tests of
salesforce and i didn't understand it.
They are all lookup filters it's just whether or not the user can use the filter optionally or bypass the filter(optional) or if the user is restricted to only selections based on the filter(required) and dependant reference a field on the source object so basically using a field on the source object to filter the choices from the target objects as outlined in the third example below.
Administrators specify the restrictions by configuring filter criteria that compare fields and values on:
The current record (source)
The lookup object (target)
The user's record, permissions, and role
Records directly related to the target object
For example, you can:
Restrict the Account Name field on opportunities to allow only accounts with a record type of Customer, filtering out Partner and Competitor.
Restrict the Account Name field on opportunities to allow only active accounts.
Restrict the Contact field on cases to allow only contacts associated with the account specified in the Account Name field on the case record.
Restrict the Account Name field on cases to allow only users with the “International Sales” profile to create or edit cases for accounts outside the United States.
A dependent lookup is a relationship field with a lookup filter that references fields on the source object. For example, you can configure the case Contact field to only show contacts associated with the account selected in the case Account Name field.
When a user changes the value of a referenced field on the source object, Salesforce immediately verifies that the value in the dependent lookup still meets the lookup filter criteria. If the value doesn't meet the criteria, an error message is displayed and users can't save the record until the value is valid.
If the referenced field on the source object is a lookup, master-detail, or hierarchy field, users can't change its value by typing. Instead, users must click the lookup icon and select a value in the lookup search dialog.
Administrators can make lookup filters required or optional.
For fields with required lookup filters, only values that match the lookup filter criteria appear in the lookup dialog. Also, users can't save invalid values manually typed in the field when editing the record. If a user tries to save an invalid value, Salesforce displays an error message, which administrators can customize.
For fields with optional lookup filters, only values that match the lookup filter criteria appear in the lookup dialog initially; however, users can click the Show all results link in the lookup dialog to remove the filter and view all search result values for the lookup field. Also, optional lookup filters allow users to save values that don't match the lookup filter criteria, and Salesforce does not display an error message if a user tries to save such values.