# Create a Custom App to Call App Runtime REST API
This section demonstrates how a **Custom Application** can interact with ONEWEB through the **App Runtime REST API** to retrieve entity data.\
The example uses a **Work Order entity** and shows a complete flow from authentication to displaying results in a custom UI.
***
### Objective
By the end of this section, you will understand how to:
* Authenticate using App Runtime REST API
* Retrieve entity data using REST endpoints
* Pass key parameters through the request URL
* Use REST responses in a Custom Application
* Display returned JSON data in the UI
***
### Use Case Overview
**Use case:**\
A Custom Application needs to retrieve **Work Order** information from ONEWEB and display related customer contact data using REST APIs.
***
### Step‑by‑Step: Get Entity Data Using REST API
***
#### Step 1: Configure Entity for REST Access
Create an Entity in **App Designer** named **Work Order**.
In this example:
* The entity contains **3 Tabs**
* Includes **4 Modules**
* Is configured to expose data through App Runtime APIs
***
#### Step 2: Identify Key Field for Query
Determine the **key field** used to retrieve entity data via REST.
In this example:
* Key field: `SALE_ORDER_NO`
* Key value: `0000000010`
This value will be passed as a query parameter to the REST API.
***
#### Step 3: Login to Obtain Authentication Token
Before calling entity APIs, authenticate using the **Login REST API**.
**Request**
* **Method:** POST
* **URL:**
```
http://localhost:9084/eaf-rest/login
```
* **Headers:**
```
Content-Type: application/json
```
* **Body (JSON):**
```
JSON{
"username": "administrator",
"password": "P@55w0rd",
"clientId": "123456789"
}
```
**Response**
* The system returns an **id\_token**
* This token must be used for authorization in subsequent API calls
***
#### Step 4: Call Entity GET API
Construct the GET request to retrieve data from the entity.
**URL Format**
```
ServerName:Port/ContextRoot/entity/{entityID}/get
```
**Example**
```
http://localhost:9084/eaf-rest/entity/EN_431959963131500/get
?handleForm=Y
&SALE_ORDER_NO=0000000010
&cbMethod=callback
```
***
#### Step 5: Set Required HTTP Headers
Include the following headers in the request:
```
Content-Type: application/json
Authorization: Bearer
clientId: 123456789
```
***
#### Step 6: Execute Requests and Receive JSON Response
After successful authentication and API call, the App Runtime responds with **JSON data** representing the entity.
***
#### Understanding Response Structure
The response JSON typically includes:
* `ENTITY_ID` – Entity identifier
* `MODULE_ID` – Module identifier
* `UPDATE` – Operation mode
* `SALE_ORDER_ITEM` – Table or module name
* Field names such as:
* `PRODUCT_ID`
* `PRODUCT_NAME`
* `KEY` – Primary key for records
This structured response allows Custom Apps to navigate and extract relevant information programmatically.
***
### Test API from a Custom Application
Now let’s simulate a **real Custom App flow** that uses JavaScript and AJAX to consume the App Runtime API.
***
#### Step 1: Login Screen
The user enters credentials in the Custom App UI and triggers a login request.
***
#### Step 2: Store Token in Session
Use **AJAX** to:
* Call Login REST API
* Store `id_token` securely in session or memory for reuse
***
#### Step 3: Input Order Number in UI
Prepare a screen where users can input a **Sales Order Number**.
***
#### Step 4: Trigger Entity API Call
User enters an Order No and clicks **Find Customer Contact**.
***
#### Step 5: Call REST API via JavaScript
Use JavaScript / AJAX to:
* Call the entity GET API
* Pass `SALE_ORDER_NO`
* Include headers:
* Content-Type
* Authorization (Bearer token)
* clientId
***
#### Step 6: Extract Required Data from JSON
Navigate the JSON response to retrieve:
```
MODULE_ID → UPDATE → SALE_ORDER_DELIVERY → CUST_CONTACT
```
This value represents the **Customer Contact** associated with the work order.
***
#### Step 7: Display Result in UI
Use JavaScript or JQuery to render the retrieved data on the screen.
***
### Summary
This example demonstrates how a **Custom Application** can:
* Authenticate via App Runtime REST API
* Retrieve entity data using key‑based queries
* Consume REST responses in JSON format
* Display backend data dynamically in a custom UI
By using **App Runtime REST APIs**, ONEWEB applications can act as powerful backend services for:
* Web apps
* Mobile apps
* Third‑party systems
---
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