added foreign key constraint support to SQLite

.travis.yml

@@ -14,7 +14,7 @@ install:
 before_script:
 - mysql -e 'CREATE DATABASE IF NOT EXISTS test;'
 - psql -c 'create database test;' -U postgres
-- touch test.db
+- touch test.db test1.db
 script: python tests/sql.py
 after_script: rm -f test.db
 jobs:

setup.py

@@ -16,5 +16,5 @@
     package_dir={"": "src"},
     packages=["cs50"],
     url="https://github.com/cs50/python-cs50",
-    version="2.4.0"
+    version="2.4.1"
 )

src/cs50/sql.py

@@ -5,6 +5,7 @@
 import os
 import re
 import sqlalchemy
+import sqlite3
 import sqlparse
 import sys
 import termcolor
@@ -32,12 +33,25 @@ def __init__(self, url, **kwargs):
             if not os.path.isfile(matches.group(1)):
                 raise RuntimeError("not a file: {}".format(matches.group(1)))
 
-        # Create engine, raising exception if back end's module not installed
-        self.engine = sqlalchemy.create_engine(url, **kwargs)
+            # Remember foreign_keys and remove it from kwargs
+            foreign_keys = kwargs.pop("foreign_keys", False)
+
+            # Create engine, raising exception if back end's module not installed
+            self.engine = sqlalchemy.create_engine(url, **kwargs)
+
+            # Enable foreign key constraints
+            if foreign_keys:
+                sqlalchemy.event.listen(self.engine, "connect", _connect)
+        else:
+
+            # Create engine, raising exception if back end's module not installed
+            self.engine = sqlalchemy.create_engine(url, **kwargs)
+
 
         # Log statements to standard error
         logging.basicConfig(level=logging.DEBUG)
         self.logger = logging.getLogger("cs50")
+        disabled = self.logger.disabled
 
         # Test database
         try:
@@ -48,7 +62,7 @@ def __init__(self, url, **kwargs):
             e.__cause__ = None
             raise e
         else:
-            self.logger.disabled = False
+            self.logger.disabled = disabled
 
     def _parse(self, e):
         """Parses an exception, returns its message."""
@@ -133,6 +147,8 @@ def process(value):
                     return process(value)
 
         # Allow only one statement at a time
+        # SQLite does not support executing many statements
+        # https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.execute
         if len(sqlparse.split(text)) > 1:
             raise RuntimeError("too many statements at once")
 
@@ -211,3 +227,16 @@ def process(value):
         else:
             self.logger.debug(termcolor.colored(log, "green"))
             return ret
+
+
+# http://docs.sqlalchemy.org/en/latest/dialects/sqlite.html#foreign-key-support
+def _connect(dbapi_connection, connection_record):
+    """Enables foreign key support."""
+
+    # Ensure backend is sqlite
+    if type(dbapi_connection) is sqlite3.Connection:
+        cursor = dbapi_connection.cursor()
+
+        # Respect foreign key constraints by default
+        cursor.execute("PRAGMA foreign_keys=ON")
+        cursor.close()

tests/sql.py

@@ -107,18 +107,26 @@ class SQLiteTests(SQLTests):
     @classmethod
     def setUpClass(self):
         self.db = SQL("sqlite:///test.db")
+        self.db1 = SQL("sqlite:///test1.db", foreign_keys=True)
 
     def setUp(self):
         self.db.execute("CREATE TABLE cs50(id INTEGER PRIMARY KEY, val TEXT)")
 
-    def multi_inserts_enabled(self):
-        return False
+    def test_foreign_key_support(self):
+        self.db.execute("CREATE TABLE foo(id INTEGER PRIMARY KEY)")
+        self.db.execute("CREATE TABLE bar(foo_id INTEGER, FOREIGN KEY (foo_id) REFERENCES foo(id))")
+        self.assertEqual(self.db.execute("INSERT INTO bar VALUES(50)"), 1)
+
+        self.db1.execute("CREATE TABLE foo(id INTEGER PRIMARY KEY)")
+        self.db1.execute("CREATE TABLE bar(foo_id INTEGER, FOREIGN KEY (foo_id) REFERENCES foo(id))")
+        self.assertEqual(self.db1.execute("INSERT INTO bar VALUES(50)"), None)
 
 if __name__ == "__main__":
     suite = unittest.TestSuite([
         unittest.TestLoader().loadTestsFromTestCase(SQLiteTests),
         unittest.TestLoader().loadTestsFromTestCase(MySQLTests),
         unittest.TestLoader().loadTestsFromTestCase(PostgresTests)
     ])
-    logging.getLogger("cs50.sql").disabled = True
+
+    logging.getLogger("cs50").disabled = True
     sys.exit(not unittest.TextTestRunner(verbosity=2).run(suite).wasSuccessful())