feat(duckdb): support sqlalchemy 2

Author: cpcloud

.github/workflows/ibis-backends.yml

@@ -454,7 +454,7 @@ jobs:
       - run: python -m pip install --upgrade pip 'poetry<1.4'
 
       - name: remove deps that are not compatible with sqlalchemy 2
-        run: poetry remove duckdb-engine snowflake-sqlalchemy
+        run: poetry remove snowflake-sqlalchemy
 
       - name: add sqlalchemy 2
         run: poetry add --lock --optional 'sqlalchemy>=2,<3'
@@ -522,6 +522,10 @@ jobs:
             extras:
               - trino
               - postgres
+          - name: duckdb
+            title: DuckDB
+            extras:
+              - duckdb
     steps:
       - name: checkout
         uses: actions/checkout@v3

ibis/backends/duckdb/__init__.py

@@ -525,7 +525,16 @@ def to_pyarrow_batches(
         query_ast = self.compiler.to_ast_ensure_limit(expr, limit, params=params)
         sql = query_ast.compile()
 
-        cursor = self.con.connect().execute(sql)
+        con = self.con.connect()
+
+        # end the current transaction started by sqlalchemy; without this
+        # duckdb-engine raises an exception disallowing nested transactions
+        #
+        # not clear if the value of returning a RecordBatchReader versus an
+        # iterator of record batches is worth the cursor leakage here
+        con.exec_driver_sql("COMMIT")
+
+        cursor = con.execute(sql)
 
         reader = cursor.cursor.fetch_record_batch(chunk_size=chunk_size)
         return IbisRecordBatchReader(reader, cursor)

ibis/backends/duckdb/registry.py

@@ -53,23 +53,24 @@ def _round(t, op):
 }
 
 
-def _generic_log(arg, base):
-    return sa.func.ln(arg) / sa.func.ln(base)
+def _generic_log(arg, base, *, type_):
+    return sa.func.ln(arg, type_=type_) / sa.func.ln(base, type_=type_)
 
 
 def _log(t, op):
     arg, base = op.args
+    sqla_type = t.get_sqla_type(op.output_dtype)
     sa_arg = t.translate(arg)
     if base is not None:
         sa_base = t.translate(base)
         try:
             base_value = sa_base.value
         except AttributeError:
-            return _generic_log(sa_arg, sa_base)
+            return _generic_log(sa_arg, sa_base, type_=sqla_type)
         else:
             func = _LOG_BASE_FUNCS.get(base_value, _generic_log)
-            return func(sa_arg)
-    return sa.func.ln(sa_arg)
+            return func(sa_arg, type_=sqla_type)
+    return sa.func.ln(sa_arg, type_=sqla_type)
 
 
 def _timestamp_from_unix(t, op):