Fixed issue where we call connectDatabaseToEmulator twice

.changeset/nervous-ads-pretend.md

@@ -0,0 +1,5 @@
+---
+"@firebase/database": patch
+---
+
+Fixed issue where connectDatabaseToEmulator can be called twice during a hot reload

packages/database/src/api/Database.ts

@@ -320,9 +320,11 @@ export function getDatabase(
   const db = _getProvider(app, 'database').getImmediate({
     identifier: url
   }) as Database;
-  const emulator = getDefaultEmulatorHostnameAndPort('database');
-  if (emulator) {
-    connectDatabaseEmulator(db, ...emulator);
+  if (!db._instanceStarted) {
+    const emulator = getDefaultEmulatorHostnameAndPort('database');
+    if (emulator) {
+      connectDatabaseEmulator(db, ...emulator);
+    }
   }
   return db;
 }

packages/database/test/exp/integration.test.ts

@@ -77,6 +77,24 @@ describe('Database@exp Tests', () => {
     const db = getDatabase(defaultApp);
     expect(db).to.be.ok;
   });
+  it("doesn't try to connect to emulator after database has already started", async () => {
+    const db = getDatabase(defaultApp);
+    const r = ref(db, '.info/connected');
+    const deferred = new Deferred();
+    onValue(r, snapshot => {
+      if (snapshot.val()) {
+        deferred.resolve();
+      }
+    });
+    await deferred.promise;
+    process.env.__FIREBASE_DEFAULTS__ = JSON.stringify({
+      emulatorHosts: {
+        database: 'localhost:9000'
+      }
+    });
+    expect(() => getDatabase(defaultApp)).to.not.throw();
+    delete process.env.__FIREBASE_DEFAULTS__;
+  });
 
   it('Can get database with custom URL', () => {
     const db = getDatabase(defaultApp, 'http://foo.bar.com');