Remove single relationships

.changeset/little-lemons-fail.md

@@ -0,0 +1,38 @@
+---
+"@neo4j/graphql": major
+---
+
+Single element relationships have been removed in favor of list relationships:
+
+Before
+
+```graphql
+type Movie {
+    director: Person @relationship(type: "DIRECTED", direction: "IN")
+}
+```
+
+After
+
+```graphql
+type Movie {
+    director: [Person!]! @relationship(type: "DIRECTED", direction: "IN")
+}
+```
+
+This requires updating filters, clients and auth rules to use the list filter operations.
+
+Single element relationships cannot be reliably enforced, leading to a data inconsistent with the schema. If the GraphQL model requires 1-1 relationships (such as in federations) these can now be achieved with the `@cypher` directive instead:
+
+```graphql
+type Movie {
+    director: Person
+        @cypher(
+            statement: """
+            MATCH(this)-[:ACTED_IN]->(p:Person)
+            RETURN p
+            """
+            columnName: "p"
+        )
+}
+```

packages/apollo-federation-subgraph-compatibility/src/type-defs.ts

@@ -42,39 +42,75 @@ export const typeDefs = gql`
 
     directive @custom on OBJECT
 
-    type Product @custom @key(fields: "id") @key(fields: "sku package") @key(fields: "sku variation { id }") {
+    type Product @custom @key(fields: "id") @key(fields: "sku package") @key(fields: "sku variation { id }") @node {
         id: ID!
         sku: String
         package: String
-        variation: ProductVariation @relationship(type: "HAS_VARIATION", direction: OUT)
-        dimensions: ProductDimension @relationship(type: "HAS_DIMENSIONS", direction: OUT)
-        createdBy: User @provides(fields: "totalProductsCreated") @relationship(type: "CREATED_BY", direction: OUT)
+        variation: ProductVariation
+            @cypher(
+                statement: """
+                MATCH (this)-[:HAS_VARIATION]->(res:ProductVariation)
+                RETURN res
+                """
+                columnName: "res"
+            )
+        dimensions: ProductDimension
+            @cypher(
+                statement: """
+                MATCH (this)-[:HAS_DIMENSIONS]->(res:ProductDimension)
+                RETURN res
+                """
+                columnName: "res"
+            )
+        createdBy: User
+            @provides(fields: "totalProductsCreated")
+            @cypher(
+                statement: """
+                MATCH (this)-[:CREATED_BY]->(res:User)
+                RETURN res
+                """
+                columnName: "res"
+            )
         notes: String @tag(name: "internal")
         research: [ProductResearch!]! @relationship(type: "HAS_RESEARCH", direction: OUT)
     }
 
-    type DeprecatedProduct @key(fields: "sku package") {
+    type DeprecatedProduct @key(fields: "sku package") @node {
         sku: String!
         package: String!
         reason: String
-        createdBy: User @relationship(type: "CREATED_BY", direction: OUT)
+        createdBy: User
+            @cypher(
+                statement: """
+                MATCH (this)-[:CREATED_BY]->(res:User)
+                RETURN res
+                """
+                columnName: "res"
+            )
     }
 
-    type ProductVariation {
+    type ProductVariation @node {
         id: ID!
     }
 
-    type ProductResearch @key(fields: "study { caseNumber }") {
-        study: CaseStudy! @relationship(type: "HAS_STUDY", direction: OUT)
+    type ProductResearch @key(fields: "study { caseNumber }") @node {
+        study: CaseStudy!
+            @cypher(
+                statement: """
+                MATCH (this)-[:HAS_STUDY]->(res:CaseStudy)
+                RETURN res
+                """
+                columnName: "res"
+            )
         outcome: String
     }
 
-    type CaseStudy {
+    type CaseStudy @node {
         caseNumber: ID!
         description: String
     }
 
-    type ProductDimension @shareable {
+    type ProductDimension @shareable @node {
         size: String
         weight: Float
         unit: String @inaccessible
@@ -93,7 +129,7 @@ export const typeDefs = gql`
 
     # Should be extend type as below
     # extend type User @key(fields: "email") {
-    type User @key(fields: "email") @extends {
+    type User @key(fields: "email") @node @extends {
         averageProductsCreatedPerYear: Int @requires(fields: "totalProductsCreated yearsOfEmployment")
         email: ID! @external
         name: String @override(from: "users")

packages/graphql/src/schema/create-relationship-fields/create-relationship-fields.ts

@@ -176,6 +176,7 @@ export function createRelationshipFields({
     userDefinedFieldDirectivesForNode: Map<string, Map<string, DirectiveNode[]>>;
     features?: Neo4jFeaturesSettings;
 }): void {
+    // HERE?
     const relationships =
         entityAdapter instanceof ConcreteEntityAdapter
             ? entityAdapter.relationships
@@ -190,6 +191,12 @@ export function createRelationshipFields({
             return;
         }
 
+        if (!relationshipAdapter.isList) {
+            throw new Error(
+                `@relationship on non-list field [${relationshipAdapter.source.name}.${relationshipAdapter.name}] not supported`
+            );
+        }
+
         // TODO: find a way to merge these 2 into 1 RelationshipProperties generation function
         if (relationshipAdapter instanceof RelationshipDeclarationAdapter) {
             doForRelationshipDeclaration({