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packages/cloudflare/src/db/do-dialect.ts

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+/**
+ * Kysely dialect for Durable Object preview databases
+ *
+ * Proxies all queries to an EmDashPreviewDB DO instance via RPC.
+ * Preview mode is read-only — no transaction support needed.
+ */
+
+import type {
+	CompiledQuery,
+	DatabaseConnection,
+	DatabaseIntrospector,
+	Dialect,
+	Driver,
+	Kysely,
+	QueryResult,
+} from "kysely";
+import { SqliteAdapter, SqliteQueryCompiler } from "kysely";
+
+import { D1Introspector } from "./d1-introspector.js";
+import type { QueryResult as DOQueryResult } from "./do-class.js";
+
+/**
+ * Minimal interface for the DO stub's RPC methods.
+ *
+ * We define this instead of using DurableObjectStub<EmDashPreviewDB> directly
+ * because Rpc.Result<T> resolves to `never` when the return type contains
+ * `unknown` (Record<string, unknown> in QueryResult.rows). This interface
+ * gives us clean typing without fighting the Rpc type system.
+ */
+export interface PreviewDBStub {
+	query(sql: string, params?: unknown[]): Promise<DOQueryResult>;
+}
+
+export interface PreviewDODialectConfig {
+	/**
+	 * Factory that returns a fresh DO stub on each call.
+	 *
+	 * DO stubs are bound to the request context that created them.
+	 * Since the Kysely instance may be cached across requests, we can't
+	 * hold a single stub — each connection must get a fresh one via
+	 * namespace.get(id), which is cheap (no RPC, just a local ref).
+	 */
+	getStub: () => PreviewDBStub;
+}
+
+export class PreviewDODialect implements Dialect {
+	readonly #config: PreviewDODialectConfig;
+
+	constructor(config: PreviewDODialectConfig) {
+		this.#config = config;
+	}
+
+	createAdapter(): SqliteAdapter {
+		return new SqliteAdapter();
+	}
+
+	createDriver(): Driver {
+		return new PreviewDODriver(this.#config);
+	}
+
+	createQueryCompiler(): SqliteQueryCompiler {
+		return new SqliteQueryCompiler();
+	}
+
+	createIntrospector(db: Kysely<any>): DatabaseIntrospector {
+		return new D1Introspector(db);
+	}
+}
+
+class PreviewDODriver implements Driver {
+	readonly #config: PreviewDODialectConfig;
+
+	constructor(config: PreviewDODialectConfig) {
+		this.#config = config;
+	}
+
+	async init(): Promise<void> {}
+
+	async acquireConnection(): Promise<DatabaseConnection> {
+		return new PreviewDOConnection(this.#config.getStub());
+	}
+
+	async beginTransaction(): Promise<void> {
+		// No-op. Preview is read-only.
+	}
+
+	async commitTransaction(): Promise<void> {
+		// No-op.
+	}
+
+	async rollbackTransaction(): Promise<void> {
+		// No-op.
+	}
+
+	async releaseConnection(): Promise<void> {}
+
+	async destroy(): Promise<void> {}
+}
+
+class PreviewDOConnection implements DatabaseConnection {
+	readonly #stub: PreviewDBStub;
+
+	constructor(stub: PreviewDBStub) {
+		this.#stub = stub;
+	}
+
+	async executeQuery<O>(compiledQuery: CompiledQuery): Promise<QueryResult<O>> {
+		const sqlText = compiledQuery.sql;
+		// eslint-disable-next-line typescript-eslint(no-unsafe-type-assertion) -- CompiledQuery.parameters is ReadonlyArray<unknown>, stub expects unknown[]
+		const params = compiledQuery.parameters as unknown[];
+
+		const result = await this.#stub.query(sqlText, params);
+
+		return {
+			// eslint-disable-next-line typescript-eslint(no-unsafe-type-assertion) -- Kysely generic O is the caller's row type; we trust the DB returned matching rows
+			rows: result.rows as O[],
+			numAffectedRows: result.changes !== undefined ? BigInt(result.changes) : undefined,
+		};
+	}
+
+	// eslint-disable-next-line require-yield -- interface requires AsyncIterableIterator but DO doesn't support streaming
+	async *streamQuery<O>(): AsyncIterableIterator<QueryResult<O>> {
+		throw new Error("Preview DO dialect does not support streaming");
+	}
+}