# Struct Mask (StructMaskGenerator)

The [Struct Mask](/app/generation/generators/generator-reference/struct-mask.md) generator applies selected generators to specific StructFields within a StructType in a Spark database.

## Link object structure <a href="#generator-api-struct-mask-link-object" id="generator-api-struct-mask-link-object"></a>

For the Struct Mask generator, there is a link object for each path expression value to assign a sub-generator to.

The generator does not itself support consistency or differential privacy.

The `metadata` object is populated from the [`JsonMaskMetadata`](https://app.tonic.ai/apidocs/index.html#/models/JsonMaskMetadata) object, and includes:

* `pathExpression`, which is the expression that identifies the value to apply the sub-generator to.
* The types of values to apply the sub-generator to.
* The `subGeneratorMetadata` object, which identifies and configures the selected sub-generator.

{% code overflow="wrap" %}

```json
{
  "schema": "string",
  "table": "string",
  "column": "string"
  "metadata": {
    "generatorId": "StructMaskGenerator",
    "customValueProcessor": "string" //If custom value processor applied
    "pathExpression": "string",
    "jsonFilterTypes": [ enum ],
    "subGeneratorMetadata": {
      "presetId": "string",
      "generatorId": "string",
      //Metadata for the selected sub-generator
      "customValueProcessor": "string",  //If custom value processor applied to the sub-generator
    }
}
```

{% endcode %}

## Example replacement <a href="#generator-api-struct-mask-replacement" id="generator-api-struct-mask-replacement"></a>

In the following example replacement for the StructMask generator:

* The value at the path expression `$.address.city` is assigned the Address generator. The generator is configured to produce a city value. Consistency is disabled.
* The value at the path expression `$.address.zip` is also assigned the Address generator. The generator is configured to produce a zip code value. Consistency is disabled.

```json
{
  "name": "value",
  "schema": "",
  "table": "simple_struct",
  "links": [
    {
      "schema": "",
      "table": "simple_struct",
      "column": "value",
      "metadata": {
        "generatorId": "StructMaskGenerator",
        "presetId": "StructMaskGenerator",
        "pathExpression": "$.address.city",
        "jsonFilterTypes": [
          0
        ],
        "subGeneratorMetadata": {
          "presetId": "AddressGenerator",
          "generatorId": "AddressGenerator",
          "addressType": "City",
          "isConsistent": false
        }
      }
    },
    {
      "schema": "",
      "table": "simple_struct",
      "column": "value",
      "metadata": {
        "generatorId": "StructMaskGenerator",
        "presetId": "StructMaskGenerator",
        "pathExpression": "$.address.zip",
        "jsonFilterTypes": [
          0
        ],
        "subGeneratorMetadata": {
          "presetId": "AddressGenerator",
          "generatorId": "AddressGenerator",
          "addressType": "ZipCode",
          "isConsistent": false
        }
      }
    }
  ]
}
```


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