# Map function

Use the JSONata map function to sync multiple entities dynamically. When building a solution, the number of entities to sync and the parameters for each are not always known; for example, when syncing the attachments, files, or documents for a message, there can be zero, one, or more. It is necessary to dynamically specify a list of the entities, functions, and function parameters to return from the database using an expression.

* The **basic expression** structure is `=$.map(array, function)`.
  * Specify the array you will consult, i.e., a datasource `@ctx.datasources.{datasourceName}`.
  * For the function, specify `($item)`.
  * Example of the basic structure `=$map(@ctx.datasources.{datasourceName}, function($item))`.
* After defining the basic structure, **map out** relevant properties from the array to the relevant `entity`/`function`/`parameters` and specify the dynamic entry using the `$.item` property, e.g., `"calenderId": $.item.id`. This will run through all the records in the datasource and perform a sync-entities action for each record in the table.

```yaml
# Example of dynamic sync-entities expression
actions:
  - children:
      - type: action.sync-entities
        options:
          title: Show events
          provider: DATA_PROVIDER_REST
          entities: | 
            =$map(@ctx.datasources.list-calendars-rest, function($item) {
              $.{
                "entity": "events-from-calendar"
                "function": "get-calendar-event-list"
                "parameters": {
                  "accessToken": "jigx.graph.oauth",
                  "calendarId": $item.id
                }
              }
            })[]
```


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