# 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) --- # 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://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?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.