> 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/relate-objects/lookup-object/select-lookup-reference-field.md).

# Select Lookup Reference Field

Start by selecting the parent object, then move to the child object (line item), and finally configure the lookup object that the line item refers to. When defining the lookup object, you must select the field in the line item that references the lookup object.

### How to Set Up the Lookup Object

Let’s assume you are setting up the builder for OpportunityLineItem based on the Opportunity object. As shown in the object structure diagram below, OpportunityLineItem has two key relationships:

* **Opportunity**\
  The parent object of OpportunityLineItem, referenced via the `OpportunityId` field.
* **PricebookEntry**\
  The object referenced by OpportunityLineItem for product and pricing information, linked via the `PricebookEntryId` field.

<figure><img src="/files/e93pxJTdtnMCO2rXtcXN" alt=""><figcaption></figcaption></figure>

#### Step 1: Select the Parent Object

Choose **Opportunity** as the parent object.

<figure><img src="/files/Uaxns3Sa3WUI2rmcvf8l" alt=""><figcaption></figcaption></figure>

#### Step 2: Select the Line Item Object

Choose **OpportunityLineItem** as the line item object.

<figure><img src="/files/DGug9D81etelFM8j1J2W" alt=""><figcaption></figcaption></figure>

#### <mark style="color:orange;">Step 3: Define the Lookup Object</mark>

Since **OpportunityLineItem references PricebookEntry**, select the <mark style="color:orange;">`PricebookEntryId`</mark> field in the line item object as the lookup reference field.

<figure><img src="/files/UlHZNMaheXie78jUnpyB" alt=""><figcaption></figcaption></figure>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://help.smallbuilder.com/smallbuilder-line-items/builder/builder-setup-steps/relate-objects/lookup-object/select-lookup-reference-field.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.