List input to @connection fields parameter

Which Category is your question related to? API, GraphQL, schema defnitions, documentation

Amplify CLI Version 4.24.0

What AWS Services are you utilizing? API

Provide additional details e.g. code snippets Hi guys, I have a type of relation in my data that I have been trying to solve for quite a while now. I have gone over the documentation but could find any information on how to achieve the desired result.

Lets say that I have two @models, one for Characters and one for Items. Characters can own items, which means there is a one way connection. If we are restricted to just a single item per character, I could define the schema like below:

type Character @model
{
    id: ID!
    itemId: String
    item: Item @connection(fields: ["itemId"])
}
type Item @model
{
    id: ID!
}

In this, multiple characters could own the same item, but there wouldn’t have to be any duplicate entries in the item database (because the characters point to the same object).

But now to my question, how do I achieve this kind of relation when a character can own many items? My hope was that I could do something like this:

type Character @model
{
    id: ID!
    itemIds: [String]
    items: [Item] @connection(fields: ["itemIds"])
}
type Item @model
{
    id: ID!
}

and that the resolver would loop over itemIds in order to fetch all of the items specified. However, as you can probably guess it does not work in this way and does not accept list inputs. So what is the recommended approach for these kinds of relations?

[RossWilliams]

There are two approaches.

1. Create a many-to-many mapping. This means having a CharacterItems model that holds connections to both the Character and Items model. This has a latency impact, as there is another round trip to the database.
2. Create a custom resolver for Character.items.req.vtl instead of the auto-generated one created when you use the @connection directive. In your custom resolver, use a BatchGet dynamodb operation to get all items in your items list. There is an AppSync tutorial on using BatchGet / TransactGet in templates. Using this approach, you are limited to 100 items, so choose it if you have a bounded list of items < 100.

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