added the examples/check.py file

Author: jprakash-db

examples/check.py

@@ -0,0 +1,119 @@
+"""
+databricks-sql-connector includes a SQLAlchemy dialect compatible with Databricks SQL.
+It aims to be a drop-in replacement for the crflynn/sqlalchemy-databricks project, that implements
+more of the Databricks API, particularly around table reflection, Alembic usage, and data
+ingestion with pandas.
+
+Expected URI format is: databricks+thrift://token:dapi***@***.cloud.databricks.com?http_path=/sql/***
+
+Because of the extent of SQLAlchemy's capabilities it isn't feasible to provide examples of every
+usage in a single script, so we only provide a basic one here. More examples are found in our test
+suite at tests/e2e/sqlalchemy/test_basic.py and in the PR that implements this change: 
+
+https://github.com/databricks/databricks-sql-python/pull/57
+
+# What's already supported
+
+Most of the functionality is demonstrated in the e2e tests mentioned above. The below list we
+derived from those test method names:
+
+    - Create and drop tables with SQLAlchemy Core
+    - Create and drop tables with SQLAlchemy ORM
+    - Read created tables via reflection
+    - Modify column nullability
+    - Insert records manually
+    - Insert records with pandas.to_sql (note that this does not work for DataFrames with indexes)
+
+This connector also aims to support Alembic for programmatic delta table schema maintenance. This
+behaviour is not yet backed by integration tests, which will follow in a subsequent PR as we learn
+more about customer use cases there. That said, the following behaviours have been tested manually:
+
+    - Autogenerate revisions with alembic revision --autogenerate
+    - Upgrade and downgrade between revisions with `alembic upgrade <revision hash>` and
+      `alembic downgrade <revision hash>`
+
+# Known Gaps
+    - MAP, ARRAY, and STRUCT types: this dialect can read these types out as strings. But you cannot
+      define a SQLAlchemy model with databricks.sqlalchemy.dialect.types.DatabricksMap (e.g.) because
+      we haven't implemented them yet.
+    - Constraints: with the addition of information_schema to Unity Catalog, Databricks SQL supports
+      foreign key and primary key constraints. This dialect can write these constraints but the ability
+      for alembic to reflect and modify them programmatically has not been tested.
+"""
+
+import os
+import sqlalchemy
+from sqlalchemy.orm import Session
+from sqlalchemy import Column, String, Integer, BOOLEAN, create_engine, select
+
+try:
+    from sqlalchemy.orm import declarative_base
+except ImportError:
+    from sqlalchemy.ext.declarative import declarative_base
+
+host = os.getenv("MY_SERVER_HOSTNAME")
+http_path = os.getenv("MY_HTTP_PATH")
+access_token = os.getenv("MY_TOKEN")
+catalog = os.getenv("MY_CATALOG")
+schema = "jprakash"
+
+
+# Extra arguments are passed untouched to the driver
+# See thrift_backend.py for complete list
+extra_connect_args = {
+    "_tls_verify_hostname": True,
+    "_user_agent_entry": "PySQL Example Script",
+}
+
+if sqlalchemy.__version__.startswith("1.3"):
+    # SQLAlchemy 1.3.x fails to parse the http_path, catalog, and schema from our connection string
+    # Pass these in as connect_args instead
+
+    conn_string = f"databricks://token:{access_token}@{host}"
+    connect_args = dict(catalog=catalog, schema=schema, http_path=http_path)
+    all_connect_args = {**extra_connect_args, **connect_args}
+    engine = create_engine(conn_string, connect_args=all_connect_args)
+else:
+    engine = create_engine(
+        f"databricks://token:{access_token}@{host}?http_path={http_path}&catalog={catalog}&schema={schema}",
+        connect_args=extra_connect_args,
+    )
+
+session = Session(bind=engine)
+base = declarative_base(bind=engine)
+
+
+class SampleObject(base):
+
+    __tablename__ = "mySampleTable"
+
+    name = Column(String(255), primary_key=True)
+    episodes = Column(Integer)
+    some_bool = Column(BOOLEAN)
+
+
+base.metadata.create_all()
+
+sample_object_1 = SampleObject(name="Bim Adewunmi", episodes=6, some_bool=True)
+sample_object_2 = SampleObject(name="Miki Meek", episodes=12, some_bool=False)
+
+session.add(sample_object_1)
+session.add(sample_object_2)
+
+session.commit()
+
+# SQLAlchemy 1.3 has slightly different methods
+if sqlalchemy.__version__.startswith("1.3"):
+    stmt = select([SampleObject]).where(
+        SampleObject.name.in_(["Bim Adewunmi", "Miki Meek"])
+    )
+    output = [i for i in session.execute(stmt)]
+else:
+    stmt = select(SampleObject).where(
+        SampleObject.name.in_(["Bim Adewunmi", "Miki Meek"])
+    )
+    output = [i for i in session.scalars(stmt)]
+
+assert len(output) == 2
+
+base.metadata.drop_all()