> For the complete documentation index, see [llms.txt](https://help.smallbuilder.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.smallbuilder.com/smallbuilder-line-items/builder/builder-setup-steps/setup-line-item-editor/source-field-assigning-default-values-from-parent-or-lookup-fields.md).
# Source Field: Assigning Default Values from Parent or Lookup Fields
When adding Line Items, you can assign specific field values from the Parent Object or Lookup Object as default values.
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Source field values are only assigned **when a Line Item is added for the first time.**
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### Example: Assigning Unit Price from PricebookEntry as Default Value for Opportunity Products
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This example demonstrates the configuration of a Line Item Editor for Opportunity Products:
* **Parent:** Opportunity
* **Line Item:** OpportunityLineItem
* **Lookup:** PricebookEntry
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When adding Opportunity Products, assign the selected product’s Unit Price as the default value for the Unit Price field in the Line Item.
The Line Item includes both List Price and Unit Price fields. These fields will be populated with values from the Unit Price field in the Lookup Object (PricebookEntry).
#### Configuration Steps
1. In the source field setting for List Price and Unit Price, select Lookup as the first option.
2. For the second option, select Unit Price.
#### Result
The selected products’ Unit Price is assigned as the default value to the List Price and Unit Price fields in the Line Item.