fix(server-core): Handle empty query in getSqlGenerator (#9270)

api-gateway calls getSqlGenerator with empty query and concrete data source to initialize SQL API
But because query is empty `sqlGenerator.dataSource` can be undefined, and it would trigger re-creating query with new data source, which would be `default`

packages/cubejs-server-core/src/core/CompilerApi.js

@@ -137,19 +137,26 @@ export class CompilerApi {
       throw new Error(`Unknown dbType: ${dbType}`);
     }
 
+    // sqlGenerator.dataSource can return undefined for query without members
+    // Queries like this are used by api-gateway to initialize SQL API
+    // At the same time, those queries should use concrete dataSource, so we should be good to go with it
     dataSource = compilers.compiler.withQuery(sqlGenerator, () => sqlGenerator.dataSource);
-    const _dbType = await this.getDbType(dataSource);
-    if (dataSource !== 'default' && dbType !== _dbType) {
-      // TODO consider more efficient way than instantiating query
-      sqlGenerator = await this.createQueryByDataSource(
-        compilers,
-        query,
-        dataSource,
-        _dbType
-      );
+    if (dataSource !== undefined) {
+      const _dbType = await this.getDbType(dataSource);
+      if (dataSource !== 'default' && dbType !== _dbType) {
+        // TODO consider more efficient way than instantiating query
+        sqlGenerator = await this.createQueryByDataSource(
+          compilers,
+          query,
+          dataSource,
+          _dbType
+        );
 
-      if (!sqlGenerator) {
-        throw new Error(`Can't find dialect for '${dataSource}' data source: ${_dbType}`);
+        if (!sqlGenerator) {
+          throw new Error(
+            `Can't find dialect for '${dataSource}' data source: ${_dbType}`
+          );
+        }
       }
     }
 

packages/cubejs-testing/test/__snapshots__/smoke-multidb.test.ts.snap

@@ -1,5 +1,21 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`multidb SQL pushdown queries to different data sources: Products 1`] = `
+Array [
+  Object {
+    "name": "apples",
+  },
+]
+`;
+
+exports[`multidb SQL pushdown queries to different data sources: Suppliers 1`] = `
+Array [
+  Object {
+    "company": "Fruits Inc",
+  },
+]
+`;
+
 exports[`multidb query: query 1`] = `
 Array [
   Object {

packages/cubejs-testing/test/smoke-multidb.test.ts

@@ -3,6 +3,7 @@ import { MysqlDBRunner, PostgresDBRunner } from '@cubejs-backend/testing-shared'
 import cubejs, { CubeApi } from '@cubejs-client/core';
 // eslint-disable-next-line import/no-extraneous-dependencies
 import { afterAll, beforeAll, expect, jest } from '@jest/globals';
+import { Client as PgClient } from 'pg';
 import { BirdBox, getBirdbox } from '../src';
 import {
   DEFAULT_API_TOKEN,
@@ -11,12 +12,43 @@ import {
   JEST_BEFORE_ALL_DEFAULT_TIMEOUT,
 } from './smoke-tests';
 
+// TODO: Random port?
+const pgPort = 5656;
+let connectionId = 0;
+
+async function createPostgresClient(user: string, password: string) {
+  connectionId++;
+  const currentConnId = connectionId;
+
+  console.debug(`[pg] new connection ${currentConnId}`);
+
+  const conn = new PgClient({
+    database: 'db',
+    port: pgPort,
+    host: '127.0.0.1',
+    user,
+    password,
+    ssl: false,
+  });
+  conn.on('error', (err) => {
+    console.log(err);
+  });
+  conn.on('end', () => {
+    console.debug(`[pg] end ${currentConnId}`);
+  });
+
+  await conn.connect();
+
+  return conn;
+}
+
 describe('multidb', () => {
   jest.setTimeout(60 * 5 * 1000);
   let db: StartedTestContainer;
   let db2: StartedTestContainer;
   let birdbox: BirdBox;
   let client: CubeApi;
+  let connection: PgClient;
 
   beforeAll(async () => {
     db = await PostgresDBRunner.startContainer({});
@@ -39,6 +71,9 @@ describe('multidb', () => {
         CUBEJS_DB_USER2: 'root',
         CUBEJS_DB_PASS2: 'Test1test',
 
+        CUBEJS_PG_SQL_PORT: `${pgPort}`,
+        CUBESQL_SQL_PUSH_DOWN: 'true',
+
         ...DEFAULT_CONFIG,
       },
       {
@@ -49,6 +84,7 @@ describe('multidb', () => {
     client = cubejs(async () => DEFAULT_API_TOKEN, {
       apiUrl: birdbox.configuration.apiUrl,
     });
+    connection = await createPostgresClient('admin', 'admin_password');
   }, JEST_BEFORE_ALL_DEFAULT_TIMEOUT);
 
   afterAll(async () => {
@@ -69,4 +105,32 @@ describe('multidb', () => {
     });
     expect(response.rawData()).toMatchSnapshot('query');
   });
+
+  test('SQL pushdown queries to different data sources: Products', async () => {
+    const res = await connection.query(`
+  SELECT
+    name
+  FROM
+    Products
+  WHERE
+    LOWER(name) = 'apples'
+  GROUP BY
+    1
+    `);
+    expect(res.rows).toMatchSnapshot();
+  });
+
+  test('SQL pushdown queries to different data sources: Suppliers', async () => {
+    const res = await connection.query(`
+  SELECT
+    company
+  FROM
+    Suppliers
+  WHERE
+    LOWER(company) = 'fruits inc'
+  GROUP BY
+    1
+    `);
+    expect(res.rows).toMatchSnapshot();
+  });
 });