# Create an Entity ## Introduction This guide explains how to create entities. **Entities** are containers into which (input) data and rules acting on that data can be integrated, as in a JavaScript `class`. Using entities is the most natural/logical way to implement a business rule in a ruleset, and therefore, they improve the manageability of your rulesets. Within an entity, data become regular properties and rules calculated properties of the entity, like in this `Person` entity: * `Name` (regular property) * `Address` (regular property) * `DateOfBirth` (regular property) * `Age` (calculated property – rule) ### Elementary and compound entities The `Person` entity is self-contained and therefore a so-called **elementary entity**. Elementary entities cover many real-world business rule scenarios, but Rulecube goes even further with **compound entities** that are composed of two or more connected entities to cover all possible business scenarios. For example, a compound `Invoice` entity consists of its own properties and properties based on the `InvoiceItem` entity, where one invoice can have one or more items. Furthermore, the `InvoiceItem` entity is connected to the `ProductItem` entity that holds product details: **`Invoice`** (entity):\ `InvoiceDate`\ `TotalAmount`\ `InvoiceItems` -> **`InvoiceItem`** (entity):\ `Count`\ `Amount`\ `Product` -> **`ProductItem`** (entity):\ `ProductID`\ `Description`\ `Price` This way, you can cover each data structure you need in your rulesets. ## Procedure Let's create a compound entity because if you master that, you'll also know how to create elementary entities. You'll create the compound `Invoice` entity as shown above, including the calculation of `Amount` at the `InvoiceItem` level and the `TotalAmount` at the Invoice level. For compound entities, it's necessary to work bottom-up because parent entities require child entities to be available. So, first, create `ProductItem`, then `InvoiceItem`, and finally, `Invoice`: ### Step 1: Create the `ProductItem` entity 1. Create a ruleset named `TotalInvoiceAmount`. 2. Create an entity named `entProductItem`. 3. Click **Add property**.\ ↳ The **Input/Property** page opens. 4. In The **Name** field, enter `ProductID`. And in the **Type** list, select `string`. 5. Save the property. 6. Repeat steps 3 to 5 to create the `Description` property as a `string` and the `Price` property as a `number`.\ ↳ Finally, your entity should look like this:
### Step 2: Create the `InvoiceItem` entity 1. Create an entity named `entInvoiceItem`. 2. Add a property named `Count` (**Type**=`number`). 3. Add a property named Product. And in the **Type** list, select `entProductItem`.\ ↳ Now, `entInvoiceItem` and `entProductItem` are connected, and `entInvoiceItem` has become a compound entity. Rulecube shows this with a little cube icon in front of the `entInvoiceItem` entity:
4. Add a calculated property for `Amount` (**Type**=`number`) and set its **Expression** to:
```javascript Count * Product.Price ``` \ **Explanation**\ Because `entInvoiceItem` and `entProductItem` are connected, you can use the `Product.Price` to calculate the amount for invoice items.
5. Save the entity.\ ↳ The content of `entInvoiceItem` should look like this:
Notice that Rulecube places the of *input* in front of regular properties and the ![](/files/LxkpHh3R7gTAst1x4oA1) of *rule* in front of calculated properties. ### Step 3: Create the `Invoice` entity 1. Create an entity named `entInvoice`. 2. Add a property named `InvoiceItems` and set its **Type** to `array` with **Sub type** = `entInvoiceItem`.\ ↳ By defining this property as an array, an invoice can have multiple items. Furthermore, `entInvoice` and `entInvoiceItem` are connected now. And because `entInvoiceItem` is connected to `entProductItem`, `entInvoice` is also connected to `entProductItem`. 3. Add a calculated property for `TotalAmount` (**Type**=`number`) and set its **Expression** to:
```javascript InvoiceItems.sum(item => item.Amount) ``` \ **Explanation**\ This is an [arrow function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions) that summarizes all the item amounts into the `TotalAmount`.
4. Save the entity.\ ↳ Your compound entity structure now should look like this:
### Step 4: Test your ruleset [Try out the ruleset](/how-to-guides/ruleset-development/try-out-a-ruleset.md) and enter input like this: ```json { "Invoice": { "InvoiceItems": [ { "Product": { "ProductID": "PK-207-U", "Description": "Rubber bands", "Price": 11.75 }, "Count": 8 }, { "Product": { "ProductID": "KD-883-J", "Description": "6mm tube - 1mtr", "Price": 5.15 }, "Count": 5 } ] } } ``` After executing, you should get a result like this: ```json { "InvoiceItems": [ { "Product": { "ProductID": "PK-207-U", "Description": "Rubber bands", "Price": 11.75 }, "Count": 8, "Amount": 94 }, { "Product": { "ProductID": "KD-883-J", "Description": "6mm tube - 1mtr", "Price": 5.15 }, "Count": 5, "Amount": 25.75 } ], "TotalAmount": 119.75 } ``` With the amount calculated per item and the total amount calculated for the invoice. ## Additional resources If you have a JSON schema or an XSD for your entity structure, Rulecube has a much easier and quicker way to create entities as described in the [Drag and Drop](/how-to-guides/ruleset-development/entities/drag-and-drop-a-json-schema-or-xsd-to-create-entities.md) guide. --- # Agent Instructions: 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: ``` GET https://docs.rulecube.com/how-to-guides/ruleset-development/entities/create-an-entity.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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.