{
  "customers": [
    {
      "id": 1,
      "name": "bob",
      "orders": [{"id": 1, "customerId": 1, "itemId": 6}]
    },
    {
      "id": 2,
      "name": "jane",
      "orders": [{"id": 2, "customerId": 2, "itemId": 7}]
    }
  ]
}

...odata/customers?$expand=orders&$filter=orders/any(order: order/itemId eq 6)

{
  "customers": [
    {
      "id": 1,
      "name": "bob",
      "orders": [{"id": 1, "customerId": 1, "itemId": 6}]
    },
    {
      "id": 2,
      "name": "jane",
      "orders": []
    }
  ]
}

{
  "customers": [
    {
      "id": 1,
      "name": "bob",
      "orders": [{"id": 1, "customerId": 1, "itemId": 6}]
    }
  ]
}