MCP DuckDB Knowledge Graph Memory Server

Instructions

Implementation Reference

• src/manager.ts:630-716 (handler)

  Implementation of the openNodes method in KnowledgeGraphManager. Retrieves entities by names using SQL queries, groups observations, fetches related relations, and returns a KnowledgeGraph.
  async openNodes(names: string[]): Promise<KnowledgeGraph> { if (names.length === 0) { return { entities: [], relations: [] }; } try { using conn = await this.getConn(); // Create placeholders const placeholders = names.map(() => "?").join(","); // Retrieve entities and observations at once using LEFT JOIN const reader = await conn.executeAndReadAll( ` SELECT e.name, e.entityType, o.content FROM entities e LEFT JOIN observations o ON e.name = o.entityName WHERE e.name IN (${placeholders}) `, names ); const rows = reader.getRows(); // Group results by entity const entitiesMap = new Map<string, Entity>(); for (const row of rows) { const name = row[0] as string; const entityType = row[1] as string; const content = row[2] as string | null; if (!entitiesMap.has(name)) { // Create a new entity entitiesMap.set(name, { name, entityType, observations: content ? [content] : [], }); } else if (content) { // Add observation to existing entity entitiesMap.get(name)!.observations.push(content); } } const entities = Array.from(entitiesMap.values()); // Create a set of entity names const entityNames = entities.map((entity) => entity.name); // Get related relations if (entityNames.length > 0) { const placeholders = entityNames.map(() => "?").join(","); const relationsReader = await conn.executeAndReadAll( ` SELECT from_entity as "from", to_entity as "to", relationType FROM relations WHERE from_entity IN (${placeholders}) OR to_entity IN (${placeholders}) `, [...entityNames, ...entityNames] ); const relationsData = relationsReader.getRows(); // Convert results to an array of Relation objects const relations = relationsData.map((row: any) => { return { from: row[0] as string, to: row[1] as string, relationType: row[2] as string, }; }); return { entities, relations, }; } else { return { entities, relations: [], }; } } catch (error: unknown) { this.logger.error("Error opening nodes", extractError(error)); return { entities: [], relations: [] }; } }
• src/server.ts:184-204 (registration)

  Registers the 'open_nodes' MCP tool with server.tool, defining input schema (array of strings for names) and delegating execution to knowledgeGraphManager.openNodes.
  server.tool( "open_nodes", "Open specific nodes in the knowledge graph by their names", { names: z .array(z.string()) .describe("An array of entity names to retrieve"), }, async ({ names }) => ({ content: [ { type: "text", text: JSON.stringify( await knowledgeGraphManager.openNodes(names), null, 2 ), }, ], }) );
• src/types.ts:63-63 (schema)

  TypeScript interface definition for the openNodes method in KnowledgeGraphManager.
  openNodes(names: string[]): Promise<KnowledgeGraph>;