Dask interface: Accept and forward the new if-exists query param

The new `if-exists` query parameter will be forwarded to Dask's
`to_sql()` method. By default, `influxio` will use `fail`.

When targeting the SQLAlchemy database interface, the target table will
be created automatically, if it does not exist. The `if-exists` URL
query parameter can be used to configure this behavior. The default
value is `fail`.

* fail: Raise a ValueError.
* replace: Drop the table before inserting new values.
* append: Insert new values to the existing table.

CHANGES.rst

@@ -5,6 +5,8 @@ Changelog
 
 in progress
 ===========
+- Dask interface: Accept and forward the new ``if-exists`` URL query
+  parameter to Dask's ``to_sql()`` method.
 
 2024-06-13 v0.3.1
 =================

README.rst

@@ -287,6 +287,29 @@ keystrokes on subsequent invocations.
     influxio copy "${SOURCE}" "${TARGET}"
 
 
+Parameters
+==========
+
+``if-exists``
+-------------
+When targeting the SQLAlchemy database interface, the target table will be
+created automatically, if it does not exist. The ``if-exists`` URL query
+parameter can be used to configure this behavior. The default value is
+``fail``.
+
+* fail: Raise a ValueError.
+* replace: Drop the table before inserting new values.
+* append: Insert new values to the existing table.
+
+Example usage:
+
+.. code-block:: shell
+
+    influxio copy \
+        "http://example:token@localhost:8086/testdrive/demo" \
+        "crate://crate@localhost:4200/testdrive?table=demo&if-exists=replace"
+
+
 *******************
 Project information
 *******************

examples/export_sqlalchemy.py

@@ -41,7 +41,7 @@ def main():
     logger.info("Transferring data")
     for df in influx.read_df():
         logger.info("Loading data frame into RDBMS/SQL database using pandas/Dask")
-        dataframe_to_sql(df, dburi=DBURI, tablename="demo", progress=True)
+        dataframe_to_sql(df, dburi=DBURI, tablename="demo", if_exists="replace", progress=True)
 
     # Read back data from target database.
     logger.info("Reading back data from the target database")

influxio/adapter.py

@@ -271,7 +271,8 @@ def __init__(self, url: t.Union[URL, str], progress: bool = False, debug: bool =
         if isinstance(url, str):
             url: URL = URL(url)
 
-        self.database, self.table = SqlAlchemyAdapter.decode_database_table(url)
+        self.database, self.table = self.decode_database_table(url)
+        self.if_exists = url.query.get("if-exists")
 
         # Special handling for SQLite and CrateDB databases.
         self.dburi = str(url.with_query(None))
@@ -301,9 +302,13 @@ def write(self, source: t.Union[pd.DataFrame, InfluxDbApiAdapter]):
         logger.info("Loading dataframes into RDBMS/SQL database using pandas/Dask")
         if isinstance(source, InfluxDbApiAdapter):
             for df in source.read_df():
-                dataframe_to_sql(df, dburi=self.dburi, tablename=self.table, progress=self.progress)
+                dataframe_to_sql(
+                    df, dburi=self.dburi, tablename=self.table, if_exists=self.if_exists, progress=self.progress
+                )
         elif isinstance(source, pd.DataFrame):
-            dataframe_to_sql(source, dburi=self.dburi, tablename=self.table, progress=self.progress)
+            dataframe_to_sql(
+                source, dburi=self.dburi, tablename=self.table, if_exists=self.if_exists, progress=self.progress
+            )
         else:
             raise NotImplementedError(f"Failed handling source: {source}")
 
@@ -329,13 +334,15 @@ def create_database(self):
     def run_sql(self, sql: str):
         engine = sa.create_engine(self.dburi)
         with engine.connect() as connection:
-            connection.connection.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
+            if hasattr(connection.connection, "set_isolation_level"):
+                connection.connection.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
             return connection.execute(sa.text(sql))
 
     def run_sql_raw(self, sql: str):
         engine = sa.create_engine(self.dburi)
         connection = engine.raw_connection()
-        connection.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
+        if hasattr(connection, "set_isolation_level"):
+            connection.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
         cursor = connection.cursor()
         cursor.execute(sql)
         result = cursor.fetchall()

influxio/io.py

@@ -97,18 +97,26 @@ def dataframe_to_sql(
     tablename: str,
     index=False,
     chunksize=None,
-    if_exists="replace",
+    if_exists="fail",
     npartitions: int = None,
     progress: bool = False,
 ):
     """
     Load pandas dataframe into database using Dask.
 
     https://stackoverflow.com/questions/62404502/using-dasks-new-to-sql-for-improved-efficiency-memory-speed-or-alternative-to
+
+    if_exists : {'fail', 'replace', 'append'}, default 'fail'
+        How to behave if the table already exists.
+
+        * fail: Raise a ValueError.
+        * replace: Drop the table before inserting new values.
+        * append: Insert new values to the existing table.
     """
     import dask.dataframe as dd
 
     # Set a few defaults.
+    if_exists = if_exists or "fail"
     chunksize = chunksize or 5_000
     npartitions = npartitions or int(os.cpu_count() / 2)
 

tests/test_adapter.py

@@ -42,6 +42,15 @@ def test_cratedb_adapter_database_table():
     assert adapter.database == "testdrive"
     assert adapter.table == "basic"
     assert adapter.dburi == "crate://localhost:4200/?schema=testdrive"
+    assert adapter.if_exists is None
+
+
+def test_cratedb_adapter_if_exists():
+    adapter = SqlAlchemyAdapter.from_url("crate://localhost:4200/?database=testdrive&table=basic&if-exists=append")
+    assert adapter.database == "testdrive"
+    assert adapter.table == "basic"
+    assert adapter.dburi == "crate://localhost:4200/?schema=testdrive"
+    assert adapter.if_exists == "append"
 
 
 def test_file_adapter_ilp_file():

tests/test_export.py

@@ -21,7 +21,9 @@ def influxdb() -> InfluxDbApiAdapter:
 
 @pytest.fixture
 def cratedb() -> SqlAlchemyAdapter:
-    return SqlAlchemyAdapter.from_url(CRATEDB_URL)
+    adapter = SqlAlchemyAdapter.from_url(CRATEDB_URL)
+    adapter.run_sql("DROP TABLE IF EXISTS basic")
+    return adapter
 
 
 @pytest.fixture
@@ -63,9 +65,9 @@ def provision_influxdb(influxdb, line_protocol_file_basic):
     influxio.core.copy(source_url, target_url)
 
 
-def test_export_cratedb(caplog, influxdb, provision_influxdb, cratedb):
+def test_export_cratedb_default(caplog, influxdb, provision_influxdb, cratedb):
     """
-    Export data from InfluxDB to CrateDB.
+    Export data from InfluxDB to CrateDB, happy path.
     """
 
     source_url = INFLUXDB_API_URL
@@ -84,6 +86,78 @@ def test_export_cratedb(caplog, influxdb, provision_influxdb, cratedb):
     assert len(records) == 2
 
 
+def test_export_cratedb_fail_if_target_exists(caplog, influxdb, provision_influxdb, cratedb):
+    """
+    Exporting data from InfluxDB to CrateDB should fail if target table exists.
+    """
+
+    source_url = INFLUXDB_API_URL
+    target_url = CRATEDB_URL
+
+    # Create a table that will cause the export process to fail.
+    cratedb.run_sql("CREATE TABLE basic (foo INT)")
+
+    # Transfer data.
+    with pytest.raises(ValueError) as ex:
+        influxio.core.copy(source_url, target_url)
+    ex.match("Table 'basic' already exists.")
+
+
+def test_export_cratedb_if_exists_unknown(caplog, influxdb, provision_influxdb, cratedb):
+    """
+    Exporting data from InfluxDB to CrateDB should fail if target table exists.
+    """
+
+    source_url = INFLUXDB_API_URL
+    target_url = CRATEDB_URL + "?if-exists=Hotzenplotz"
+
+    # Create a table that will cause the export process to fail.
+    cratedb.run_sql("CREATE TABLE basic (foo INT)")
+
+    # Transfer data.
+    with pytest.raises(ValueError) as ex:
+        influxio.core.copy(source_url, target_url)
+    ex.match("'Hotzenplotz' is not valid for if_exists")
+
+
+def test_export_cratedb_if_exists_replace(caplog, influxdb, provision_influxdb, cratedb):
+    """
+    Exporting data from InfluxDB to CrateDB will succeed with ``if-exists=replace``.
+    """
+
+    source_url = INFLUXDB_API_URL
+    target_url = CRATEDB_URL + "?if-exists=replace"
+
+    # Create a table that would cause the export process to fail.
+    cratedb.run_sql("CREATE TABLE basic (foo INT)")
+
+    # Transfer data.
+    influxio.core.copy(source_url, target_url)
+
+    # Verify number of records in target database.
+    cratedb.refresh_table()
+    records = cratedb.read_records()
+    assert len(records) == 2
+
+
+def test_export_cratedb_if_exists_append(caplog, influxdb, provision_influxdb, cratedb):
+    """
+    Exporting data from InfluxDB to CrateDB twice will succeed with ``if-exists=append``.
+    """
+
+    source_url = INFLUXDB_API_URL
+    target_url = CRATEDB_URL + "?if-exists=append"
+
+    # Transfer data.
+    influxio.core.copy(source_url, target_url)
+    influxio.core.copy(source_url, target_url)
+
+    # Verify number of records in target database.
+    cratedb.refresh_table()
+    records = cratedb.read_records()
+    assert len(records) == 4
+
+
 def test_export_postgresql(caplog, influxdb, provision_influxdb, postgresql):
     """
     Export data from InfluxDB to PostgreSQL.