Merge pull request #19 from cs50/expandable-parameters

adds support for expandable parameters

Author: dmalan

cs50/sql.py

@@ -1,4 +1,6 @@
+import datetime
 import sqlalchemy
+import sys
 
 class SQL(object):
     """Wrap SQLAlchemy to provide a simple SQL API."""
@@ -14,21 +16,91 @@ def __init__(self, url):
         try:
             self.engine = sqlalchemy.create_engine(url)
         except Exception as e:
+            e.__context__ = None
             raise RuntimeError(e)
 
-    def execute(self, text, *multiparams, **params):
+    def execute(self, text, **params):
         """
         Execute a SQL statement.
         """
+
+        class UserDefinedType(sqlalchemy.TypeDecorator):
+            """
+            Add support for expandable values, a la https://bitbucket.org/zzzeek/sqlalchemy/issues/3953/expanding-parameter.
+            """
+            impl = sqlalchemy.types.UserDefinedType
+            def process_literal_param(self, value, dialect):
+                """Receive a literal parameter value to be rendered inline within a statement."""
+                def process(value):
+                    """Render a literal value, escaping as needed."""
+
+                    # bool
+                    if isinstance(value, bool):
+                        return sqlalchemy.types.Boolean().literal_processor(dialect)(value)
+
+                    # datetime.date
+                    elif isinstance(value, datetime.date):
+                        return sqlalchemy.types.String().literal_processor(dialect)(value.strftime("%Y-%m-%d"))
+
+                    # datetime.datetime
+                    elif isinstance(value, datetime.datetime):
+                        return sqlalchemy.types.String().literal_processor(dialect)(value.strftime("%Y-%m-%d %H:%M:%S"))
+
+                    # datetime.time
+                    elif isinstance(value, datetime.time):
+                        return sqlalchemy.types.String().literal_processor(dialect)(value.strftime("%H:%M:%S"))
+
+                    # float
+                    elif isinstance(value, float):
+                        return sqlalchemy.types.Float().literal_processor(dialect)(value)
+
+                    # int
+                    elif isinstance(value, int):
+                        return sqlalchemy.types.Integer().literal_processor(dialect)(value)
+
+                    # long
+                    elif sys.version_info.major != 3 and isinstance(value, long):
+                        return sqlalchemy.types.Integer().literal_processor(dialect)(value)
+
+                    # str
+                    elif isinstance(value, str):
+                        return sqlalchemy.types.String().literal_processor(dialect)(value)
+
+                    # None
+                    elif isinstance(value, sqlalchemy.sql.elements.Null):
+                        return sqlalchemy.types.NullType().literal_processor(dialect)(value)
+
+                    # unsupported value
+                    raise RuntimeError("unsupported value")
+
+                # process value(s), separating with commas as needed
+                if type(value) is list:
+                    return ", ".join([process(v) for v in value])
+                else:
+                    return process(value)
+
         try:
 
-            # bind parameters before statement reaches database, so that bound parameters appear in exceptions
-            # http://docs.sqlalchemy.org/en/latest/core/sqlelement.html#sqlalchemy.sql.expression.text
-            # https://groups.google.com/forum/#!topic/sqlalchemy/FfLwKT1yQlg
-            # http://docs.sqlalchemy.org/en/latest/core/connections.html#sqlalchemy.engine.Engine.execute
+            # construct a new TextClause clause
+            statement = sqlalchemy.text(text)
+
+            # iterate over parameters
+            for key, value in params.items():
+
+                # translate None to NULL
+                if value is None:
+                    value = sqlalchemy.sql.null()
+
+                # bind parameters before statement reaches database, so that bound parameters appear in exceptions
+                # http://docs.sqlalchemy.org/en/latest/core/sqlelement.html#sqlalchemy.sql.expression.text
+                statement = statement.bindparams(sqlalchemy.bindparam(key, value=value, type_=UserDefinedType()))
+
+            # stringify bound parameters
             # http://docs.sqlalchemy.org/en/latest/faq/sqlexpressions.html#how-do-i-render-sql-expressions-as-strings-possibly-with-bound-parameters-inlined
-            statement = sqlalchemy.text(text).bindparams(*multiparams, **params)
-            result = self.engine.execute(str(statement.compile(compile_kwargs={"literal_binds": True})))
+            self.statement = str(statement.compile(compile_kwargs={"literal_binds": True}))
+
+            # execute statement
+            result = self.engine.execute(self.statement)
 
             # if SELECT (or INSERT with RETURNING), return result set as list of dict objects
             if result.returns_rows:
@@ -49,4 +121,5 @@ def execute(self, text, *multiparams, **params):
 
         # else raise error
         except Exception as e:
+            e.__context__ = None
             raise RuntimeError(e)