skip invalid default bind

CHANGES.rst

@@ -5,6 +5,8 @@ Unreleased
 
 -   Export typing information instead of using external typeshed definitions.
     :issue:`1112`
+-   If default engine options are set, but ``SQLALCHEMY_DATABASE_URI`` is not set, an
+    invalid default bind will not be configured. :issue:`1117`
 
 
 Version 3.0.0

src/flask_sqlalchemy/extension.py

@@ -294,7 +294,7 @@ def init_app(self, app: Flask) -> None:
         if basic_uri is not None:
             basic_engine_options["url"] = basic_uri
 
-        if basic_engine_options:
+        if "url" in basic_engine_options:
             engine_options.setdefault(None, {}).update(basic_engine_options)
 
         if not engine_options:

tests/test_engine.py

@@ -68,7 +68,7 @@ def test_url_type(app: Flask, value: str | sa.engine.URL) -> None:
     assert str(db.engines["a"].url) == "sqlite://"
 
 
-def test_no_default_url(app: Flask) -> None:
+def test_no_binds_error(app: Flask) -> None:
     del app.config["SQLALCHEMY_DATABASE_URI"]
 
     with pytest.raises(RuntimeError) as info:
@@ -78,6 +78,15 @@ def test_no_default_url(app: Flask) -> None:
     assert str(info.value) == e
 
 
+@pytest.mark.usefixtures("app_ctx")
+def test_no_default_url(app: Flask) -> None:
+    del app.config["SQLALCHEMY_DATABASE_URI"]
+    app.config["SQLALCHEMY_BINDS"] = {"a": "sqlite://"}
+    db = SQLAlchemy(app, engine_options={"echo": True})
+    assert None not in db.engines
+    assert "a" in db.engines
+
+
 @pytest.mark.usefixtures("app_ctx")
 def test_sqlite_relative_path(app: Flask) -> None:
     app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///test.db"