> ## Documentation Index
> Fetch the complete documentation index at: https://docs.alumio.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Array or object: Inherit from data

> Fills missing keys in the array or object from the supplied data.

Fills in any keys that are missing from the incoming array or object using a set of default values you supply. Anything already present in the input is kept as-is; only the gaps are filled from your defaults. Use this to guarantee that certain fields always exist, for example making sure every product carries a default colour, size, or material even when the source system left them out.

The fill happens at every level, so nested objects are completed as well, not just the top-level keys.

This documentation describes: [Schema](/schemas/mapper/list-inherit-from)

## Fields

**Array**

Required

The default values to fall back on, entered as JSON. Any key listed here that is not already present in the input is added with the value you provide. Where a key exists in both, the input keeps its own value and your default is ignored.

## Sample data

| Field | Value |
| - | - |
| Array | `{ "color": "black", "size": "One size", "material": "cotton" }` |

Input:

```json theme={null}
{ "attributes": { "color": "red", "size": "M" } }
```

Output:

```json theme={null}
{ "attributes": { "color": "red", "size": "M", "material": "cotton" } }
```

The input already had `color` and `size`, so those are kept untouched. Only the missing `material` is filled in from the supplied defaults.

```json Configuration theme={null}
{
  "prototype": "list-inherit-from",
  "parameters": {
    "array": {
      "color": "black",
      "size": "One size",
      "material": "cotton"
    }
  }
}
```


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