> For the complete documentation index, see [llms.txt](https://doc.wearepatchworks.com/product-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.wearepatchworks.com/product-documentation/process-flows/building-process-flows/process-flow-shapes/standard-shapes/map-shape/mappings-tips-and-tricks/mapping-array-fields.md). # Mapping array fields ## Introduction This page provides guidance on mapping array fields, where the value from another field needs to be added to the array output. To achieve this, wildcard (`*`) syntax is used to navigate and transform the JSON structure. Each asterisk represents a level in the data hierarchy, so you can copy values from parent objects into nested array elements without explicitly naming field names. When an asterisk encounters an array, it means *apply to every element in the array*. This enables you to propagate data from higher levels down into all elements within nested arrays. ## Need to know * Each asterisk (`*`) represents one level of depth in the JSON structure. * When an asterisk encounters an array, it applies to every element in that array. * Field names are used to navigate to specific elements in the structure. * The pattern reads from left to right, with each component specifying the next\ step in the traversal. * Values are copied from higher levels down to lower levels, not moved or\ deleted from their original location ## Example 1 (top-level array) Consider the example below: {% code lineNumbers="true" %} ```json { "category": 1111, "fruit": [ { "sku": "apples", "qty": 2 }, { "sku": "pears", "qty": 2 } ] } ``` {% endcode %} We can map the `fruit` field very simply, as below:


Mapping rule
Output `{ "fruit": [ { "sku": "apples", "qty": 2 }, { "sku": "pears", "qty": 2 } ] }`

Mapping rule

Output

{
  "fruit": [
    {
      "sku": "apples",
      "qty": 2
    },
    {
      "sku": "pears",
      "qty": 2
    }
  ]
}

### The problem Suppose we want to add the `category` field value to each item in the array, so the output is as shown below: ```json { "fruit": [ { "sku": "apples", "qty": 2, "category": 1111 }, { "sku": "pears", "qty": 2, "category": 1111 } ] } ``` ### The solution We can achieve this with the mapping rules below:

These rules can be summarised as follows:

Mapping rule	Summary
`fruit` ➤ `fruit`	The field mapping sequence matters. Before we can add a field value to another element, that element must be mapped. In this example, we need to add the `category` value to each item in the `fruit` array, so we map the `fruit` field first.
`category` ➤ `..*.category`	The field name to add/update in each item. Here we use wildcards to traverse the JSON structure.

#### JSON traversal The `*.*.*.category` target mapping traverses the JSON structure as follows:

Expression	JSON traversal
*	Start at the root: `{category: 1111, fruit:[...]}`
*	Enter the `fruit` array.
*	Access every item in the `fruit` array: `{"sku": "apples","qty": 2},{"sku": "pears","qty": 2}`
category	Add the `category` value (`1111`) to each array item.

## Example 2 (nested array) Consider the example below: {% code lineNumbers="true" %} ```json { "category": 1111, "fruit": [ { "sku": "apples", "qty": 2, "options":[{"type:":"pink lady"},{"type:":"granny smith"},{"type:":"russet"}] }, { "sku": "pears", "qty": 2, "options":[{"type:":"conference"},{"type:":"blush gold"}] } ] } ``` {% endcode %} ### The problem Suppose we want to add the `category` field value to each item in the second array (`options`), so the output is as shown below: ```json { "fruit": [ { "sku": "apples", "qty": 2, "options": [ { "type:": "pink lady", "category": 1111 }, { "type:": "granny smith", "category": 1111 }, { "type:": "russet", "category": 1111 } ] }, { "sku": "pears", "qty": 2, "options": [ { "type:": "conference", "category": 1111 }, { "type:": "blush gold", "category": 1111 } ] } ] } ``` ### The solution We can achieve this with the mapping rules below:

These rules can be summarised as follows:

Mapping rule	Summary
`fruit` ➤ `fruit`	The field mapping sequence matters. Before we can add a field value to another element, that element must be mapped. In this example, we need to add the `category` value to each item in the `fruit` array, so we map the `fruit` field first.
`category` ➤ `...options..category`	The field name to add/update in each item. Here we use wildcards to traverse the JSON structure.

#### JSON traversal The `*.*.*.options.*.category` target mapping traverses the JSON structure as follows:

Expression	JSON traversal
*	Start at the root: `{category: 1111, fruit:[...]}`
*	Enter the `fruit` array.
*	Access every item in the `fruit` array: `{"sku": "apples","qty": 2},{"sku": "pears","qty": 2, options: [...]}`
options	Access the `options` array in each `fruit` item.
*	Apply to all items in the `options` array.
category	Add the `category` value (`1111`) to each `options` array item.

## Related pages * [The array join transform function](/product-documentation/process-flows/building-process-flows/process-flow-shapes/standard-shapes/map-shape/working-with-field-transformations/available-transform-functions/array-transform-functions/array-join-transform-function.md)