Creating multiple documents within single operation while using the ref of one

Help
1

Hello!

I’m trying to create 2 documents within the same operation. The goal is to have one of them link to another via the ref. How can I do that?

Currently I’ve tried the following approach:

Map(
  [
    [
      "collection1",
      {
        coll1Prop1: "12345",
      }
    ],
    [
      "collection2",
      {
        collection1Ref: Call(Function("getDocRefByProp1"), "12345"),
        collection2Prop2: "randomProp"
      }
    ]
  ],
  Lambda(["collection", "data"],
    Create(
      Collection(Var("collection")),
      {
        data: Var("data")
      }
    )
  )
)

In this example I’m also using a Function getDocRefByProp1, which, as the name implies, returns the ref of document from collection1 by coll1Prop1 property.

I’m currently getting the following error:

Error: [
  {
    "position": [
      "collection",
      1,
      1,
      "object",
      "collection1Ref"
    ],
    "code": "call error",
    "description": "Calling the function resulted in an error.",
    "cause": [
      {
        "position": [
          "expr",
          "from"
        ],
        "code": "instance not found",
        "description": "Set not found."
      }
    ]
  }
]

Thank you in advance!

2

Hi Robert!

The error message shows that the problem occurs when calling the function. Can you share its current definition?

3

Hi Ewan, thanks for the prompt reply!

Here’s the function that’s being called:

Query(
  Lambda(
    "x",
    Select("ref", Get(Match(Index("docs_by_prop1"), Var("x"))))
  )
)

The index used is the following:

{
  name: "docs_by_prop1",
  unique: true,
  serialized: true,
  source: "collection1",
  terms: [
    {
      field: ["data", "coll1Prop1"]
    }
  ]
}

Am I right assuming that I’m trying to access a reference of a document which is not yet created within the transaction? If that’s the case, how can I add a reference to a document within the same transaction that it’s created?

4

When you create a document without a specified document ID, Fauna creates one for you:

> Create(Collection("foo"), { data: { bar: "xyzzy" }})
{
  ref: Ref(Collection("foo"), "332011350435824162"),
  ts: 1652889547700000,
  data: { bar: 'xyzzy' }
}

Notice that calling Create returns the document that was just created. So, you can do this:

> Select("ref", Create(Collection("foo"), { data: { bar: "xyzzy" }}))
Ref(Collection("foo"), "332011408194535970")

That’s most useful in a Let expression:

> Let(
  {
    newDocument:  Create(Collection("foo"), { data: { bar: "xyzzy" }}),
    newRef: Select("ref", Var("newDocument"))
  },
  {
    newDocument: Var("newDocument"),
    newRef: Var("newRef")
  }
)
{
  newDocument: {
    ref: Ref(Collection("foo"), "332011532657361442"),
    ts: 1652889721480000,
    data: { bar: 'xyzzy' }
  },
  newRef: Ref(Collection("foo"), "332011532657361442")
}

Another approach would be to call NewId to have a new document ID created:

> NewId()
'332011582404952610'

Then you can create a document with that document ID:

> Let(
  {
    newID: NewId(),
    newDocument: Create(
      Ref(Collection("foo"), Var("newID")),
      { data: { bar: "xyzzy" }}
    ),
    newRef: Select("ref", Var("newDocument"))
  },
  {
     newID: Var("newID"),
     newDocument: Var("newDocument"),
     newRef: Var("newRef")
  }
)
{
  newID: '332011779266708002',
  newDocument: {
    ref: Ref(Collection("foo"), "332011779266708002"),
    ts: 1652889956670000,
    data: { bar: 'xyzzy' }
  },
  newRef: Ref(Collection("foo"), "332011779266708002")
}

Using NewId might be useful if you need to work with that document ID before the document is actually created.

5

Awesome! I replaced my Map with Let and utilized the bindings. Thank you so much for helping me out :slight_smile:

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6

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