database.py

@@ -0,0 +1,140 @@
+"""This module contains functionality for interacting with a PostgreSQL database. It will automatically handle error
+conditions (i.e. missing columns) without terminating the entire program. Use the :py:class:`DBConnector` class to
+handle database interactions, either as a standalone object or in a context manager."""
+from __future__ import annotations
+
+import os
+import psycopg2
+from psycopg2 import DatabaseError, OperationalError
+from psycopg2.errors import UndefinedColumn
+
+DB_ADDRESS = os.getenv('DB_ADDRESS', 'localhost')
+DB_PORT = os.getenv('DB_PORT', 5432)
+DB_USER = os.getenv('DB_USER', 'postgres')
+DB_PASSWORD = os.getenv('DB_PASSWORD', '')
+DB_NAME = os.getenv('DB_NAME', 'postgres')
+DB_TABLE = os.getenv('DB_TABLE', 'cables')
+
+
+class DBConnector:
+    """Context managed database class. Use with statements to automatically open and close the database connection, like
+    so:
+
+    .. code-block:: python
+       with DBConnector() as db:
+           db.read()
+    """
+
+    def _db_start(self):
+        """Setup the database connection and cursor."""
+        try:
+            self.conn = psycopg2.connect(
+                f"host={DB_ADDRESS} port={DB_PORT} dbname={DB_NAME} user={DB_USER} password={DB_PASSWORD}")
+            self.cur = self.conn.cursor()
+        except OperationalError as e:
+            raise e
+
+    def _db_stop(self):
+        """Close the cursor and connection."""
+        self.cur.close()
+        self.conn.close()
+
+    def __init__(self):
+        self._db_start()
+
+    def __del__(self):
+        self._db_stop()
+
+    def __enter__(self):
+        self._db_start()
+
+    def __exit__(self):
+        self._db_stop()
+
+    def _get_cols(self) -> set[str]:
+        """Get the list of columns in the database.
+
+        :return: A list of column names."""
+        query = f"select COLUMN_NAME from information_schema.columns where table_name={DB_TABLE}"
+        rows = {x["COLUMN_NAME"] for x in self._query(query)}
+        return rows
+
+    def _column_parity(self, columns: list[str] | set[str]) -> set[str]:
+        """If the listed columns are not in the database, add them.
+
+        :param columns: The columns we expect are in the database.
+        :return: The list of columns in the database after querying."""
+        cols = set(columns)
+        existing = self._get_cols()
+        needs = cols.difference(existing.intersection(cols))
+        if len(needs) > 0:
+            query = f"ALTER TABLE {DB_TABLE} {', '.join([f'ADD COLUMN {c}' for c in needs])}"
+            self._query(query)
+            existing = self._get_cols()
+        return existing
+
+    def _query(self, sql) -> list[dict]:
+        """Basic function for running queries.
+
+        :param sql: SQL query as plaintext.
+        :return: Results of the query, or an empty list if none."""
+        result = []
+        try:
+            self.cur.execute(sql)
+            result = self._read_dict()
+        except DatabaseError as e:
+            print(f"ERROR {e.pgcode}: {e.pgerror}\n"
+                  f"Caused by query: {sql}")
+        finally:
+            return result
+
+    def _read_dict(self) -> list[dict]:
+        """Read the cursor as a list of dictionaries. psycopg2 defaults to using a list of tuples, so we want to convert
+        each row into a dictionary before we return it."""
+        cols = [i.name for i in self.cur.description]
+        results = []
+        for row in self.cur:
+            row_dict = {}
+            for i in range(0, len(row)):
+                if row[i]:
+                    row_dict = {**row_dict, cols[i]: row[i]}
+            results.append(row_dict)
+        return results
+
+    def read(self, **kwargs) -> list[dict]:
+        """Read rows from a database that match the specified filters.
+
+        :param kwargs: Column constraints; i.e. what value to filter by in what column.
+        :returns: A list of dictionaries of all matching rows, or an empty list if no match."""
+        args = []
+        for kw in kwargs.keys():
+            args.append(f"{kw} ILIKE {kwargs['kw']}")
+        query = f"SELECT * FROM {DB_TABLE}"
+        if len(args) > 0:
+            query += f" WHERE {' AND '.join(args)}"
+        return self._query(query)
+
+    def write(self, **kwargs) -> dict:
+        """Write a row to the database.
+
+        :param kwargs: Values to write for each database; specify each column separately!
+        :returns: The row you just added."""
+        self._column_parity(set(kwargs.keys()))
+        values = []
+        for val in kwargs.keys():
+            values.append(kwargs[val])
+        query = f"INSERT INTO {DB_TABLE} ({', '.join(kwargs.keys())}) VALUES ({', '.join(values)})"
+        self._query(query)
+        return kwargs
+
+    def write_all(self, items: list[dict]) -> list[dict]:
+        """Write multiple rows to the database.
+
+        :param items: Rows to write, as a list of dictionaries.
+        :returns: The rows that were added successfully."""
+        successes = []
+        for i in items:
+            res0 = self.write(**i)
+            if res0:
+                successes.append(res0)
+        return successes