GraphQL @connection section:

Definition

    directive @connection(keyName: String, fields: [String!]) on FIELD_DEFINITION

Has one (One-to-One)

    type Project @model {
    id: ID!
    name: String
    team: Team @connection
    }

    type Team @model {
    id: ID!
    name: String!
    }

Has many (uni-directional One-to-Many)

    type Post @model {
    id: ID!
    title: String!
    comments: [Comment] @connection(keyName: "byPost", fields: ["id"])
    }

    type Comment @model
    @key(name: "byPost", fields: ["postID", "content"]) {
    id: ID!
    postID: ID!
    content: String!
    }

Belongs to (bi-directional One-to-Many)

    type Post @model {
    id: ID!
    title: String!
    comments: [Comment] @connection(keyName: "byPost", fields: ["id"])
    }

    type Comment @model
    @key(name: "byPost", fields: ["postID", "content"]) {
    id: ID!
    postID: ID!
    content: String!
    post: Post @connection(fields: ["postID"])
    }

Many-to-many connections

    type Post @model {
    id: ID!
    title: String!
    editors: [PostEditor] @connection(keyName: "byPost", fields: ["id"])
    }

    type PostEditor
    @model(queries: null)
    @key(name: "byPost", fields: ["postID", "editorID"])
    @key(name: "byEditor", fields: ["editorID", "postID"]) {
    id: ID!
    postID: ID!
    editorID: ID!
    post: Post! @connection(fields: ["postID"])
    editor: User! @connection(fields: ["editorID"])
    }

    type User @model {
    id: ID!
    username: String!
    posts: [PostEditor] @connection(keyName: "byEditor", fields: ["id"])
    }

resources:

https://docs.amplify.aws/cli/graphql-transformer/connection/#connection