The Miru API uses expansions to retrieve related objects in a single request rather than making multiple API calls. This simplifies code and minimizes the number of API calls. Response objects only include the core fields by default. Related objects (like the device associated with a config instance) have their IDs included but not their full object data. Using the expand[] query parameter, you can include related objects directly in the response. Expansions are powerful but add some latency. As such, they should be used strategically to balance performance with the data needed in an individual request.

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Object Expansions

Many response objects contain references to objects that are not included in the default response. For example, a config instance has the following default response structure: 
{
  "object": "config_instance",
  "id": "cfg_inst_123",
  "target_status": "created",
  "activity_status": "created",
  "error_status": "none",
  "status": "created",
  "relative_filepath": "/v1/motion-control.json",
  "created_at": "2021-01-01T00:00:00Z",
  "updated_at": "2021-01-01T00:00:00Z",
  "device_id": "dvc_123",
  "config_schema_id": "cfg_sch_123",
  "config_type_id": "cfg_type_123",
  "device": null,
  "config_schema": null,
  "config_type": null,
  "content": null,
}
The device, config_schema, config_type, and content objects are not included in the config instance response by default. To retrieve the device for a given config instance, you could make two separate requests:
  • First, fetch the config instance using the config instance ID (assuming you already know the ID).
  • Then, having obtained the device_id from the config instance response, fetch the device using the device ID.
This is workable but adds both latency and complexity to your code. A better approach is to use the expand[] parameter to include the device object directly in the config instance response, avoiding a second request. The following request expands the device field using expand[]=device : 
curl --request GET \
--url https://configs.api.miruml.com/v1/config_instances/cfg_inst_123?expand[]=device \
--header 'X-API-Key: <api-key>'
With the expansion, the response includes the device that the config instance belongs to, reducing the request count from two to one. To see a full list of expandable fields for an object, look for the expand[] parameter in the Query Parameters section of the API endpoint you are querying.

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Multiple Expansions

You can expand multiple fields by passing in multiple expand[] parameters separated by & . The following request expands both the device and content fields of the config instance using expand[]=device&expand[]=content. 
  curl --request GET \
    --url https://configs.api.miruml.com/v1/config_instances/cfg_inst_123?expand[]=device&expand[]=content \
    --header 'X-API-Key: <api-key>'

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Nested Expansions

When expanding an object, it’s often the case that the expanded object contains objects that can also expand. For example, config instances can expand their config schema, which in turn can expand their config type. To expand nested objects, use the dot (.) notation within the expand[] parameter. The following request expands the config_type inside the config_schema of the config instance using expand[]=config_schema.config_type : 
  curl --request GET \
    --url https://configs.api.miruml.com/v1/config_instances/cfg_inst_123?expand[]=config_schema.config_type \
    --header 'X-API-Key: <api-key>'
Expansions cannot be nested beyond four levels deep. expand[]=field1.field2.field3.field4 is the maximum depth.
When expanding nested fields, there’s no need to expand the parent field. Since the config schema must be expanded to expand its config type in the expand[]=config_schema.config_type query parameter, the config_schema field is automatically expanded as well.

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List Expansions

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Items

When listing config instances, you can expand fields in the same way you would for a single config instance. By default, listing config instances returns the following response structure. 
{
  "object": "list",
  "total_count": -1,
  "limit": 10,
  "offset": 0,
  "has_more": true,
  "data": [
    {
      "object": "config_instance",
      "id": "cfg_inst_123",
      ...
      "content": null,
    },
    {
      "object": "config_instance",
      "id": "cfg_inst_456",
      ...
      "content": null,
    },
    ...
  ],
}
To expand the content field for every config instance in a list response, use the expand[]=content, just as you would for a single object. Unlike other APIs you may encounter, you don’t need to prefix the field with data. (e.g., expand[]=data.content). Miru automatically applies the expansion to each item in the list, not the list itself. The following request expands the content field for every config instance in the list using expand[]=content: : 
  curl --request GET \
    --url 'https://configs.api.miruml.com/v1/config_instances?expand[]=content' \
    --header 'X-API-Key: <api-key>'

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Total Count

The total_count field in a list response represents the total number of items matching the query. Because Miru paginates list responses, this number is often greater than the number of items actually returned in a single page. If a list query matches 100 items but the limit parameter is set to 10, the list response would contain only 10 items despite the total count being 100. By default, Miru does not compute total_count to avoid performance overhead. Instead, the field is set to -1 unless explicitly expanded. To include the actual total count in the response, add expand[]=total_count to the request: 
  curl --request GET \
    --url 'https://configs.api.miruml.com/v1/config_instances?expand[]=total_count' \
    --header 'X-API-Key: <api-key>'
Computing the total count can add significant latency, especially for large datasets. Only use it when necessary!