Add bulk operations utilities

app/src/db/__init__.py

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+__all__ = ["bulk_ops"]

app/src/db/bulk_ops.py

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+"""Bulk database operations for performance.
+
+Provides a bulk_upsert function
+"""
+from typing import Any, Sequence
+
+import psycopg
+from psycopg import rows, sql
+
+Connection = psycopg.Connection
+Cursor = psycopg.Cursor
+kwargs_row = rows.kwargs_row
+
+
+def bulk_upsert(
+    cur: psycopg.Cursor,
+    table: str,
+    attributes: Sequence[str],
+    objects: Sequence[Any],
+    constraint: str,
+    update_condition: sql.SQL = sql.SQL(""),
+):
+    """Bulk insert or update a sequence of objects.
+
+    Insert a sequence of objects, or update on conflict.
+    Write data from one table to another.
+    If there are conflicts due to unique constraints, overwrite existing data.
+
+    Args:
+      cur: the Cursor object from the pyscopg library
+      table: the name of the table to insert into or update
+      attributes: a sequence of attribute names to copy from each object
+      objects: a sequence of objects to upsert
+      constraint: the table unique constraint to use to determine conflicts
+      update_condition: optional WHERE clause to limit updates for a
+        conflicting row
+    """
+    temp_table = f"temp_{table}"
+    create_temp_table(cur, temp_table=temp_table, src_table=table)
+    bulk_insert(cur, table=temp_table, columns=attributes, objects=objects)
+    write_from_table_to_table(
+        cur,
+        src_table=temp_table,
+        dest_table=table,
+        columns=attributes,
+        constraint=constraint,
+        update_condition=update_condition,
+    )
+
+
+def create_temp_table(cur: psycopg.Cursor, temp_table: str, src_table: str):
+    """
+    Create table that lives only for the current transaction.
+    Use an existing table to determine the table structure.
+    Once the transaction is committed the temp table will be deleted.
+    Args:
+      temp_table: the name of the temporary table to create
+      src_table: the name of the existing table
+    """
+    cur.execute(
+        sql.SQL(
+            "CREATE TEMP TABLE {temp_table}\
+      (LIKE {src_table})\
+      ON COMMIT DROP"
+        ).format(
+            temp_table=sql.Identifier(temp_table),
+            src_table=sql.Identifier(src_table),
+        )
+    )
+
+
+def bulk_insert(
+    cur: psycopg.Cursor,
+    table: str,
+    columns: Sequence[str],
+    objects: Sequence[Any],
+):
+    """
+    Write data from a sequence of objects to a temp table.
+    This function uses the PostgreSQL COPY command which is highly performant.
+    Args:
+      cur: the Cursor object from the pyscopg library
+      table: the name of the temporary table
+      columns: a sequence of column names that are attributes of each object
+      objects: a sequence of objects with attributes defined by columns
+    """
+    columns_sql = sql.SQL(",").join(map(sql.Identifier, columns))
+    query = sql.SQL("COPY {table}({columns}) FROM STDIN").format(
+        table=sql.Identifier(table),
+        columns=columns_sql,
+    )
+    with cur.copy(query) as copy:
+        for obj in objects:
+            values = [getattr(obj, column) for column in columns]
+            copy.write_row(values)
+
+
+def write_from_table_to_table(
+    cur: psycopg.Cursor,
+    src_table: str,
+    dest_table: str,
+    columns: Sequence[str],
+    constraint: str,
+    update_condition: sql.SQL = sql.SQL(""),
+):
+    """
+    Write data from one table to another.
+    If there are conflicts due to unique constraints, overwrite existing data.
+    Args:
+      cur: the Cursor object from the pyscopg library
+      src_table: the name of the table that will be copied from
+      dest_table: the name of the table that will be written to
+      columns: a sequence of column names to copy over
+      constraint: the arbiter constraint to use to determine conflicts
+      update_condition: optional WHERE clause to limit updates for a
+        conflicting row
+    """
+    columns_sql = sql.SQL(",").join(map(sql.Identifier, columns))
+    update_sql = sql.SQL(",").join(
+        [
+            sql.SQL("{column} = EXCLUDED.{column}").format(
+                column=sql.Identifier(column),
+            )
+            for column in columns
+        ]
+    )
+    query = sql.SQL(
+        "INSERT INTO {dest_table}({columns})\
+    SELECT {columns} FROM {src_table}\
+    ON CONFLICT ON CONSTRAINT {constraint} DO UPDATE SET {update_sql}\
+      {update_condition}"
+    ).format(
+        dest_table=sql.Identifier(dest_table),
+        columns=columns_sql,
+        src_table=sql.Identifier(src_table),
+        constraint=sql.Identifier(constraint),
+        update_sql=update_sql,
+        update_condition=update_condition,
+    )
+    cur.execute(query)
+
+
+__all__ = ["bulk_upsert"]

app/tests/src/db/test_bulk_ops.py

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+"""Tests for bulk_ops module"""
+import operator
+import random
+from dataclasses import dataclass
+
+from psycopg import rows, sql
+
+import src.adapters.db as db
+from src.db import bulk_ops
+
+
+def test_bulk_upsert(db_session: db.Session):
+    conn = db_session.connection().connection
+    # Override mypy, because SQLAlchemy's DBAPICursor type doesn't specify the row_factory attribute, or that it functions as a context manager
+    with conn.cursor(row_factory=rows.class_row(Number)) as cur:  # type: ignore
+        table = "temp_table"
+        attributes = ["id", "num"]
+        objects = [get_random_number_object() for i in range(100)]
+        constraint = "temp_table_pkey"
+
+        # Create a table for testing bulk upsert
+        cur.execute(
+            sql.SQL(
+                "CREATE TEMP TABLE {table}"
+                "("
+                "id TEXT NOT NULL,"
+                "num INT,"
+                "CONSTRAINT {constraint} PRIMARY KEY (id)"
+                ")"
+            ).format(
+                table=sql.Identifier(table),
+                constraint=sql.Identifier(constraint),
+            )
+        )
+
+        bulk_ops.bulk_upsert(
+            cur,
+            table,
+            attributes,
+            objects,
+            constraint,
+        )
+        conn.commit()
+
+        # Check that all the objects were inserted
+        cur.execute(
+            sql.SQL("SELECT id, num FROM {table} ORDER BY id ASC").format(
+                table=sql.Identifier(table)
+            )
+        )
+        records = cur.fetchall()
+        objects.sort(key=operator.attrgetter("id"))
+        assert records == objects
+
+        # Now modify half of the objects
+        for obj in objects[: int(len(objects) / 2)]:
+            obj.num = random.randint(1, 10000)
+
+        bulk_ops.bulk_upsert(
+            cur,
+            table,
+            attributes,
+            objects,
+            constraint,
+        )
+        conn.commit()
+
+        # Check that the objects were updated
+        cur.execute(
+            sql.SQL("SELECT id, num FROM {table} ORDER BY id ASC").format(
+                table=sql.Identifier(table)
+            )
+        )
+        records = cur.fetchall()
+        objects.sort(key=operator.attrgetter("id"))
+        assert records == objects
+
+
+@dataclass
+class Number:
+    id: str
+    num: int
+
+
+def get_random_number_object() -> Number:
+    return Number(
+        id=str(random.randint(1000000, 9999999)),
+        num=random.randint(1, 10000),
+    )