# Is there a way of assigning a UID to a field with type string OR can I sort the parent node by an edge UID in GraphQL? **URL:** \ **Category:** Dgraph Cloud\ **Tags:** graphql, kind:question\ **Created:** [March 15, 2023, 12:39pm UTC](https://discuss.dgraph.io/t/is-there-a-way-of-assigning-a-uid-to-a-field-with-type-string-or-can-i-sort-the-parent-node-by-an-edge-uid-in-graphql/18385 "2023-03-15T12:39:40Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Poolshark](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/poolshark/32/10074_2.png) [@Poolshark](https://discuss.dgraph.io/u/Poolshark)\ **Post date:** [March 15, 2023, 12:39pm UTC](https://discuss.dgraph.io/t/is-there-a-way-of-assigning-a-uid-to-a-field-with-type-string-or-can-i-sort-the-parent-node-by-an-edge-uid-in-graphql/18385/1 "2023-03-15T12:39:40Z")
Consider the following schema ```gql interface Sortable { id: ID! sortings: [Sorting!]! } type Sorting { id: ID! sequence: Int! contextRef: String! @search(by: [exact]) } type Course { id: ID! title: String! chapters: [Chapter!] } type Chapter implements Sortable { id: ID! title: String! # from Sortable # sortings: [Sorting!]! } ``` So one `Course` can have multiple `Chapters` which again have multiple `Sortings`. I have multiple sortings because I want to allow that **one** chapter can also belong to many courses but with a **different** sorting. Here’s a sketch to visualise the data model: ![Schematic data model](https://canada1.discourse-cdn.com/flex007/uploads/dgraph/original/2X/3/373a59eb8b706d352df67c217341ada03d160bab.png) Hence the `contextRef` basically tells me in which context _(in this case type `Course`)_ one specific sorting is valid. I should mention that the context reference not necessarily needs to be the parent node! I have `contextRef` of type `String` because I need the ability to filter _sortings_ according to the scope I’m dealing with. ```gql query Course($id: ID!, $string_id: String!) { queryCourse(filter: { id: $id }) { id title chapters { id title sortings(filter: { contextRef: { eq: $string_id } }) { sequence } } } } ``` Note that `$id` and `$string_id` are **the same values** - specifically the course `UID`. So far so good. This will work but I have problems with assigning `contextRef` properly in a single `upsert` block. ### 1. Assiging a UID as a string If I create a new chapter inside a course, I would run this DQL upsert mutation. I have to run the query since the parent node of `Chapter` is not necessarily the reference node! Thus, I cannot rely on getting the correct reference UID submitted in my custom resolver. ```json { "query": "{ qCourse(func: uid()) { c as uid } }", "set": { "uid": "uid(c)", "Course.chapters": { "dgraph.type": ["Chapter", "Sortable"], "Chapter.title": "Chapter Z", "Sorting.sequence": 0, "Sorting.contextRef": "uid(c)" } } } ``` Unfortunately extracting “uid(c)” for a field of type string is prohibited and thus this is not an option. > Is there a way to assign a `UID` to a _value variable_ which can be extracted with `val()`? ### 2. Filtering by an edge UID The other approach would be having a proper **edge** to the node which serves as reference. Thus, I’d extend the schema like so ```gql interface Node { id: ID! } interface Sortable { id: ID! sortings: [Sorting!]! } type Sorting { id: ID! sequence: Int! contextRef: Node! } type Course implements Node { id: ID! title: String! chapters: [Chapter!] } type Chapter implements Sortable { id: ID! title: String! # from Sortable # sortings: [Sorting!]! } ``` Now I can easily assign the reference node to the new chapter by ```json { "query": "{ qCourse(func: uid()) { c as uid } }", "set": { "uid": "uid(c)", "Course.chapters": { "dgraph.type": ["Chapter", "Sortable"], "Chapter.title": "Chapter Z", "Sortable.sortings": { "dgraph.type": "Sorting", "Sorting.sequence": 0, "Sorting.contextRef": "uid(c)" } } } } ``` The problem is that I have no clue if I could filter by an edge UID but I guess this is not possible. ```gql query Course($id: ID!) { queryCourse(filter: { id: $id }) { id title chapters { id title sortings(filter: { contextRef: {id: $id} }) { sequence } } } } ``` > Is there a way of filtering by an edge UID? The only solution that I found so far, is having an additional `@id` field for all nodes which are referenceable and either mapping the `UID` to this field or introducing `UUIDs`. The concept with UUIDs would allow a single DQL mutation on create, whereas the “mapping” of the UID would require to generate the node first and afterwards assign the UID (as string) in a separate mutation. Any help appreciated! ---
**Author:** ![Poolshark](https://yyz1.discourse-cdn.com/flex007/user_avatar/discuss.dgraph.io/poolshark/32/10074_2.png) [@Poolshark](https://discuss.dgraph.io/u/Poolshark)\ **Post date:** [March 17, 2023, 6:07am UTC](https://discuss.dgraph.io/t/is-there-a-way-of-assigning-a-uid-to-a-field-with-type-string-or-can-i-sort-the-parent-node-by-an-edge-uid-in-graphql/18385/2 "2023-03-17T06:07:57Z")
I found the solution. Totally forgot about `@cascade`. 🙈 I can implement a `Node` interface to all types _(or at least the types I want to be referencable by `Sorting`)_. Sorting then references to Node and I a combination of `@cascade` on Sorting and `@filter` on `contextRef` does the job. Additionally, introducing the `Node` interface and applying it to **all** types has additional advantages in case you use Relay. I’ve wrote a post about this in case someone is interested > **[Support for Relay Modern](https://discuss.dgraph.io/t/support-for-relay-modern/12807/28)** > > Hi! I know this is a little old but I found a (admittedly very questionable) workaround for Assumption 1 (also part of the GraphQL specs) that a server must provide a root field called node which returns an interface Node. Doing this, will check... ### Full example ##### Schema ```auto interface Node { id: ID! } interface Sortable { id: ID! sortings: [Sorting!]! } type Sorting { id: ID! sequence: Int! contextRef: Node! } type Course implements Node { id: ID! title: String! chapters: [Chapter!] } type Chapter implements Sortable { id: ID! title: String! # from Sortable # sortings: [Sorting!]! } ``` ##### Filtered query ```auto query CourseQuery($id: ID!) { queryCourse(filter: { id: [$id] }) { chapters { sortings @cascade(fields: ["contextRef"]) { sequence contextRef(filter: { id: [$id] }) { id } } } } } ```