RQL - Projections of linked documents in an array?

[dieeisenefaust]

How can you project the fields you want to pull from a linked document in an array within the primary document?

In an article here, an example is provided in pulling all the Product Names in the each Order (Product Name being a field that exists directly in the Order document):

from Orders
where Lines.Count > 4
select Lines[].ProductName as ProductNames, OrderedAt, ShipTo.City

which resulted in the query returning an array of only those names:

{
    "ProductNames": [
        "Ikura",
        "Gorgonzola Telino",
        "Geitost",
        "Boston Crab Meat",
        "Lakkalikööri"
    ],
    "OrderedAt": "1996-08-05T00:00:00.0000000",
    "ShipTo.City": "Cunewalde",
    "@metadata": {
        "@flags": "HasRevisions",
        "@id": "orders/26-A",
        "@last-modified": "2018-02-28T11:21:24.1689975Z",
        "@change-vector": "A:275-ZzT6GeIVUkewYXBKQ6vJ9g",
        "@projection": true,
        "@index-score": 1
    }
}

However, lets say you want to return some information from within the Product document itself.

This query works to pull back the Product document:

from Orders as o
load o.Lines[].Product as p[]
select 
{
    OrderedAt: o.OrderedAt
    Freight: o.Freight
    Product: p
}

And will return something like:

{
    "OrderedAt": "1996-07-04T00:00:00.0000000",
    "Freight": 32.38,
    "Product": [
        {
            "Name": "Queso Cabrales",
            "Supplier": "suppliers/5-A",
            "Category": "categories/4-A",
            "QuantityPerUnit": "1 kg pkg.",
            "PricePerUnit": 21,
            "UnitsInStock": 5,
            "UnitsOnOrder": 718,
            "Discontinued": false,
            "ReorderLevel": 30,
            "@metadata": {
                "@collection": "Products",
                "@counters": [
                    "⭐",
                    "⭐⭐",
                    "⭐⭐⭐",
                    "⭐⭐⭐⭐",
                    "⭐⭐⭐⭐⭐"
                ],
                "@timeseries": [
                    "INC:Views"
                ],
                "@id": "products/11-A"
            }
        },
        ...
    ]
}

Using an array index will allow you to pull back the field you want for that specific Product:

from Orders as o
load o.Lines[].Product as p[]
select 
{
    OrderedAt: o.OrderedAt
    Freight: o.Freight
    Product: p[0].Name
}

Result:

{
    "OrderedAt": "1996-07-04T00:00:00.0000000",
    "Freight": 32.38,
    "Product": "Queso Cabrales",
    "@metadata": {
        "@id": "orders/1-A",
        "@last-modified": "2018-07-27T12:11:53.0447651Z",
        "@change-vector": "A:81-x863iZJD70mi2zJ6vSEiqw",
        "@projection": true,
        "@index-score": 0
    }
}

But I want to retrieve something from each Product document.

Any of the approaches I have tried have either returned an error or null

Have tried
`
Product: p.Name (null)

Product: p[].Name (error)

Product: [p.Name] (array containing null)
`

Or is this not possible in RQL and you have to use a programming language and perform a loop?

[ayende]

You can use this, no?

from Orders as o
load o.Lines[].Product as p[]
select 
{
    OrderedAt: o.OrderedAt
    Freight: o.Freight
    ProductNames: p.map(x=>x.Name)
}

[dieeisenefaust]

That's the ticket! Thank you.

Maybe I just haven't found the right documentation, but so far I had only seen 'map' used in the coding examples, not in any RQL examples, but it makes sense since you can use javascript in your RQL queries.