# App Designer Customize

When building a real‑world application, basic **Create, Read, Update, Delete (CRUD)** operations are often not sufficient.\
Applications frequently require **additional logic**, **data validation**, and **data transformation** to support complex business rules and workflows.

In the **Order Management App (Web)**, these advanced requirements are handled at the **App Designer level** using **Customization** features.

This section introduces how App Designer can be customized to extend the default behavior of entity screens and support more advanced application needs.

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### Purpose of App Designer Customization

App Designer Customization enables developers to:

* Perform **additional data processing** before or after standard actions
* Validate data beyond basic field‑level validation
* Convert or transform data formats for display or processing
* Control UI behavior dynamically based on user role or data state
* Enforce business rules directly at the screen level

Customization allows applications to move beyond simple CRUD and become **process‑aware and rule‑driven systems**.

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### Customization in the Context of Order Management App

In the Order Management App, customization is commonly used to:

* Calculate derived values such as **total amount** or **summary price**
* Validate business conditions before saving or submitting a request
* Control field behavior (read‑only, hidden, calculated) based on workflow stage
* Prepare data before linking to **Process Designer workflows**
* Support role‑specific UI behavior (Requester, Back Office, Approver, Admin PO)

These capabilities ensure that each user role interacts with the system correctly and consistently.

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### What You Will Learn in This Section

In the following sub‑sections, you will learn how to use **App Designer Customization** to:

* Customize entity behavior beyond default actions
* Implement additional validation logic
* Handle data conversion and processing at the UI level
* Integrate customized screens with backend processes

Each example builds on the Order Management entities created earlier and demonstrates how customization improves usability and correctness.

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### Summary

**App Designer Customization** is a key capability that allows ONEWEB applications to support **complex enterprise requirements**.

Instead of relying only on basic CRUD behavior, customization enables:

* Smarter data handling
* Stronger validation
* Better alignment between UI, business rules, and workflows

In the next sections, you will explore **practical customization examples** within the **Order Management App (Web)** to see how these concepts are applied in real scenarios.


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