152 lines
3.9 KiB
Python
152 lines
3.9 KiB
Python
# SQLite3 does not support parameterized table and field names,
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# for CREATE TABLE and PRAGMA so we must use Python string formatting.
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# Applying `check_identifier` to parameters prevents SQL injection.
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import sqlite3
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from typing import NamedTuple
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DEFAULT_DB_PATH = ':memory:'
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CONNECTION = None
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SQL_TYPES = {
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int: 'INTEGER',
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str: 'TEXT',
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float: 'REAL',
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bytes: 'BLOB',
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}
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class NoConnection(Exception):
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"""Call connect() to open connection."""
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class SchemaMismatch(ValueError):
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"""The table's schema doesn't match the class."""
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def __init__(self, table_name):
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self.table_name = table_name
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class NoSuchRecord(LookupError):
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"""The given primary key does not exist."""
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def __init__(self, pk):
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self.pk = pk
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class UnexpectedMultipleResults(Exception):
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"""Query returned more than 1 row."""
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class ColumnSchema(NamedTuple):
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name: str
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sql_type: str
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def check_identifier(name):
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if not name.isidentifier():
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raise ValueError(f'{name!r} is not an identifier')
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def connect(db_path=DEFAULT_DB_PATH):
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global CONNECTION
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CONNECTION = sqlite3.connect(db_path)
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return CONNECTION
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def get_connection():
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if CONNECTION is None:
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raise NoConnection()
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return CONNECTION
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def gen_columns_sql(fields):
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for name, py_type in fields.items():
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check_identifier(name)
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try:
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sql_type = SQL_TYPES[py_type]
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except KeyError as e:
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raise ValueError(f'type {py_type!r} is not supported') from e
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yield ColumnSchema(name, sql_type)
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def make_schema_sql(table_name, fields):
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check_identifier(table_name)
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pk = 'pk INTEGER PRIMARY KEY,'
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spcs = ' ' * 4
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columns = ',\n '.join(
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f'{field_name} {sql_type}'
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for field_name, sql_type in gen_columns_sql(fields)
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)
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return f'CREATE TABLE {table_name} (\n{spcs}{pk}\n{spcs}{columns}\n)'
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def create_table(table_name, fields):
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con = get_connection()
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con.execute(make_schema_sql(table_name, fields))
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def read_columns_sql(table_name):
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con = get_connection()
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check_identifier(table_name)
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rows = con.execute(f'PRAGMA table_info({table_name!r})')
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# row fields: cid name type notnull dflt_value pk
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return [ColumnSchema(r[1], r[2]) for r in rows]
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def valid_table(table_name, fields):
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table_columns = read_columns_sql(table_name)
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return set(gen_columns_sql(fields)) <= set(table_columns)
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def ensure_table(table_name, fields):
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table_columns = read_columns_sql(table_name)
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if len(table_columns) == 0:
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create_table(table_name, fields)
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if not valid_table(table_name, fields):
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raise SchemaMismatch(table_name)
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def insert_record(table_name, fields):
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con = get_connection()
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check_identifier(table_name)
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placeholders = ', '.join(['?'] * len(fields))
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sql = f'INSERT INTO {table_name} VALUES (NULL, {placeholders})'
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cursor = con.execute(sql, tuple(fields.values()))
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pk = cursor.lastrowid
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con.commit()
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cursor.close()
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return pk
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def fetch_record(table_name, pk):
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con = get_connection()
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check_identifier(table_name)
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sql = f'SELECT * FROM {table_name} WHERE pk = ? LIMIT 2'
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result = list(con.execute(sql, (pk,)))
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if len(result) == 0:
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raise NoSuchRecord(pk)
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elif len(result) == 1:
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return result[0]
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else:
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raise UnexpectedMultipleResults()
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def update_record(table_name, pk, fields):
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check_identifier(table_name)
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con = get_connection()
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names = ', '.join(fields.keys())
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placeholders = ', '.join(['?'] * len(fields))
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values = tuple(fields.values()) + (pk,)
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sql = f'UPDATE {table_name} SET ({names}) = ({placeholders}) WHERE pk = ?'
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con.execute(sql, values)
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con.commit()
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return sql, values
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def delete_record(table_name, pk):
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con = get_connection()
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check_identifier(table_name)
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sql = f'DELETE FROM {table_name} WHERE pk = ?'
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return con.execute(sql, (pk,))
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