Improving upserts

README.rst

@@ -11,6 +11,9 @@ Getting Started
  - Write access to an empty `PostgreSQL <http://www.postgresql.org>`_ database.
  - A Python installation with `Jupyter Notebook <https://github.com/jupyter/notebook>`_ >= 5.0.
 
+PGContents will put its table in the `pgcontents` namespace. When you log onto the PostgreSQL database server, make
+sure the `pgcontents` schema is in the search path (e.g., `set search_path to 'pgcontents'`; see `PostgreSQL documentation`_).
+
 **Installation:**
 
 0. Install ``pgcontents`` from PyPI via ``pip install pgcontents``.
@@ -23,3 +26,4 @@ Demo Video
 You can see a demo of PGContents in action in `this presentation from JupyterCon 2017`_.
 
 .. _`this presentation from JupyterCon 2017` : https://youtu.be/TtsbspKHJGo?t=917
+.. _`PostgreSQL documentation` : https://www.postgresql.org/docs/14/ddl-schemas.html#DDL-SCHEMAS-PATH

pgcontents/query.py

@@ -10,6 +10,7 @@
     select,
     Unicode,
 )
+from sqlalchemy.dialects.postgresql import insert
 
 from sqlalchemy.exc import IntegrityError
 
@@ -500,41 +501,27 @@ def rename_directory(db, user_id, old_api_path, new_api_path):
 def save_file(db, user_id, path, content, encrypt_func, max_size_bytes):
     """
     Save a file.
-
-    TODO: Update-then-insert is probably cheaper than insert-then-update.
     """
     content = preprocess_incoming_content(
         content,
         encrypt_func,
         max_size_bytes,
     )
     directory, name = split_api_filepath(path)
-    with db.begin_nested() as savepoint:
-        try:
-            res = db.execute(
-                files.insert().values(
-                    name=name,
-                    user_id=user_id,
-                    parent_name=directory,
-                    content=content,
-                )
+    with db.begin_nested():
+        res = db.execute(
+            insert(files)
+            .values(
+                name=name,
+                user_id=user_id,
+                parent_name=directory,
+                content=content,
             )
-        except IntegrityError as error:
-            # The file already exists, so overwrite its content with the newer
-            # version.
-            if is_unique_violation(error):
-                savepoint.rollback()
-                res = db.execute(
-                    files.update().where(
-                        _file_where(user_id, path),
-                    ).values(
-                        content=content,
-                        created_at=func.now(),
-                    )
-                )
-            else:
-                # Unknown error.  Reraise
-                raise
+            .on_conflict_do_update(constraint="uix_filepath_username", set_={
+                "content": content,
+                "created_at": func.now()
+            })
+        )
 
     return res