Query to find connection graphs

server/src/entities/connection/connection-graph.resolver.ts

@@ -0,0 +1,15 @@
+import { Args, Query, Resolver } from "@nestjs/graphql";
+import { ConnectionGraphService } from "./connection-graph.service";
+import { FindConnectionGraph } from "./dto/find-connection-graph.dto";
+
+@Resolver()
+export class ConnectionGraphResolver {
+  constructor(private connectionGraphService: ConnectionGraphService) {}
+
+  @Query(() => FindConnectionGraph)
+  async findConnectionGraph(
+    @Args("root") root: string,
+  ): Promise<FindConnectionGraph> {
+    return this.connectionGraphService.findBySystem(root);
+  }
+}

server/src/entities/connection/connection-graph.service.ts

@@ -0,0 +1,53 @@
+import { Injectable } from "@nestjs/common";
+import { InjectModel } from "@nestjs/mongoose";
+import { Model } from "mongoose";
+import { Connection } from "./connection.model";
+import { FindConnectionGraph } from "./dto/find-connection-graph.dto";
+
+@Injectable()
+export class ConnectionGraphService {
+  constructor(
+    @InjectModel(Connection.name) private connectionModel: Model<Connection>,
+  ) {}
+
+  async findBySystem(root: string): Promise<FindConnectionGraph> {
+    const chains = await this.connectionModel.aggregate([
+      { $match: { from: root } },
+      {
+        $graphLookup: {
+          from: "connections",
+          startWith: "$to",
+          connectFromField: "to",
+          connectToField: "from",
+          as: "children",
+          depthField: "depth",
+          maxDepth: 100,
+        },
+      },
+    ]);
+
+    return {
+      root,
+      // TODO: All children are repeated in each chain. Filter or return only one list of children?
+      chains: chains.map(this.addIdsToChain),
+    };
+  }
+
+  /**
+   * Mongo's default ID's (`_id`) need to be mapped manually to GraphQL `id`
+   * fields because Mongoose does not apply the model to aggregate pipeline
+   * results.
+   */
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  private addIdsToChain(chain: any) {
+    return {
+      ...chain,
+      id: chain._id,
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      children: chain.children.map((child: any) => ({
+        ...child,
+        id: child._id,
+      })),
+    };
+  }
+}

server/src/entities/connection/connection.module.ts

@@ -1,5 +1,7 @@
 import { Module } from "@nestjs/common";
 import { MongooseModule } from "@nestjs/mongoose";
+import { ConnectionGraphResolver } from "./connection-graph.resolver";
+import { ConnectionGraphService } from "./connection-graph.service";
 import { Connection, ConnectionSchema } from "./connection.model";
 import { ConnectionResolver } from "./connection.resolver";
 import { ConnectionService } from "./connection.service";
@@ -10,7 +12,12 @@ import { ConnectionService } from "./connection.service";
       { name: Connection.name, schema: ConnectionSchema },
     ]),
   ],
-  providers: [ConnectionService, ConnectionResolver],
-  exports: [MongooseModule, ConnectionService],
+  providers: [
+    ConnectionService,
+    ConnectionResolver,
+    ConnectionGraphService,
+    ConnectionGraphResolver,
+  ],
+  exports: [MongooseModule, ConnectionService, ConnectionGraphService],
 })
 export class ConnectionModule {}

server/src/entities/connection/dto/chain-root.dto.ts

@@ -0,0 +1,12 @@
+import { Field, ObjectType, OmitType } from "@nestjs/graphql";
+import { Connection } from "../connection.model";
+import { GraphConnection } from "./graph-connection.dto";
+
+@ObjectType()
+export class ChainRoot extends OmitType(Connection, ["reverse"]) {
+  @Field()
+  reverse: string;
+
+  @Field(() => [GraphConnection])
+  children: GraphConnection[];
+}

server/src/entities/connection/dto/find-connection-graph.dto.ts

@@ -0,0 +1,11 @@
+import { Field, ObjectType } from "@nestjs/graphql";
+import { ChainRoot } from "./chain-root.dto";
+
+@ObjectType()
+export class FindConnectionGraph {
+  @Field()
+  root: string;
+
+  @Field(() => [ChainRoot])
+  chains: ChainRoot[];
+}

server/src/entities/connection/dto/graph-connection.dto.ts

@@ -0,0 +1,11 @@
+import { Field, ObjectType, OmitType } from "@nestjs/graphql";
+import { Connection } from "../connection.model";
+
+@ObjectType()
+export class GraphConnection extends OmitType(Connection, ["reverse"]) {
+  @Field()
+  reverse: string;
+
+  @Field()
+  depth: number;
+}