Add new "expanding" feature to bindparam()

Added a new kind of :func:`.bindparam` called "expanding".  This is
for use in ``IN`` expressions where the list of elements is rendered
into individual bound parameters at statement execution time, rather
than at statement compilation time.  This allows both a single bound
parameter name to be linked to an IN expression of multiple elements,
as well as allows query caching to be used with IN expressions.  The
new feature allows the related features of "select in" loading and
"polymorphic in" loading to make use of the baked query extension
to reduce call overhead.   This feature should be considered to be
**experimental** for 1.2.

Fixes: #3953
Change-Id: Ie708414a3ab9c0af29998a2c7f239ff7633b1f6e

1 files changed, 110 insertions, 3 deletions

diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index 628e23c9e..d1b54ab01 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -552,6 +552,8 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
     # result column names
     _translate_colname = None
 
+    _expanded_parameters = util.immutabledict()
+
     @classmethod
     def _init_ddl(cls, dialect, connection, dbapi_connection, compiled_ddl):
         """Initialize execution context for a DDLElement construct."""
@@ -645,6 +647,11 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
 
         processors = compiled._bind_processors
 
+        if compiled.contains_expanding_parameters:
+            positiontup = self._expand_in_parameters(compiled, processors)
+        elif compiled.positional:
+            positiontup = self.compiled.positiontup
+
         # Convert the dictionary of bind parameter values
         # into a dict or list to be sent to the DBAPI's
         # execute() or executemany() method.
@@ -652,7 +659,7 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
         if compiled.positional:
             for compiled_params in self.compiled_parameters:
                 param = []
-                for key in self.compiled.positiontup:
+                for key in positiontup:
                     if key in processors:
                         param.append(processors[key](compiled_params[key]))
                     else:
@@ -684,10 +691,97 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
                     )
 
                 parameters.append(param)
+
         self.parameters = dialect.execute_sequence_format(parameters)
 
         return self
 
+    def _expand_in_parameters(self, compiled, processors):
+        """handle special 'expanding' parameters, IN tuples that are rendered
+        on a per-parameter basis for an otherwise fixed SQL statement string.
+
+        """
+        if self.executemany:
+            raise exc.InvalidRequestError(
+                "'expanding' parameters can't be used with "
+                "executemany()")
+
+        if self.compiled.positional and self.compiled._numeric_binds:
+            # I'm not familiar with any DBAPI that uses 'numeric'
+            raise NotImplementedError(
+                "'expanding' bind parameters not supported with "
+                "'numeric' paramstyle at this time.")
+
+        self._expanded_parameters = {}
+
+        compiled_params = self.compiled_parameters[0]
+        if compiled.positional:
+            positiontup = []
+        else:
+            positiontup = None
+
+        replacement_expressions = {}
+        for name in (
+            self.compiled.positiontup if compiled.positional
+            else self.compiled.binds
+        ):
+            parameter = self.compiled.binds[name]
+            if parameter.expanding:
+                values = compiled_params.pop(name)
+                if not values:
+                    raise exc.InvalidRequestError(
+                        "'expanding' parameters can't be used with an "
+                        "empty list"
+                    )
+                elif isinstance(values[0], (tuple, list)):
+                    to_update = [
+                        ("%s_%s_%s" % (name, i, j), value)
+                        for i, tuple_element in enumerate(values, 1)
+                        for j, value in enumerate(tuple_element, 1)
+                    ]
+                    replacement_expressions[name] = ", ".join(
+                        "(%s)" % ", ".join(
+                            self.compiled.bindtemplate % {
+                                "name":
+                                to_update[i * len(tuple_element) + j][0]
+                            }
+                            for j, value in enumerate(tuple_element)
+                        )
+                        for i, tuple_element in enumerate(values)
+
+                    )
+                else:
+                    to_update = [
+                        ("%s_%s" % (name, i), value)
+                        for i, value in enumerate(values, 1)
+                    ]
+                    replacement_expressions[name] = ", ".join(
+                        self.compiled.bindtemplate % {
+                            "name": key}
+                        for key, value in to_update
+                    )
+                compiled_params.update(to_update)
+                processors.update(
+                    (key, processors[name])
+                    for key in to_update if name in processors
+                )
+                if compiled.positional:
+                    positiontup.extend(name for name, value in to_update)
+                self._expanded_parameters[name] = [
+                    expand_key for expand_key, value in to_update]
+            elif compiled.positional:
+                positiontup.append(name)
+
+        def process_expanding(m):
+            return replacement_expressions.pop(m.group(1))
+
+        self.statement = re.sub(
+            r"\[EXPANDING_(.+)\]",
+            process_expanding,
+            self.statement
+        )
+        return positiontup
+
     @classmethod
     def _init_statement(cls, dialect, connection, dbapi_connection,
                         statement, parameters):
@@ -1039,7 +1133,11 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
                     get_dbapi_type(self.dialect.dbapi)
                 if dbtype is not None and \
                         (not exclude_types or dbtype not in exclude_types):
-                    inputsizes.append(dbtype)
+                    if key in self._expanded_parameters:
+                        inputsizes.extend(
+                            [dbtype] * len(self._expanded_parameters[key]))
+                    else:
+                        inputsizes.append(dbtype)
             try:
                 self.cursor.setinputsizes(*inputsizes)
             except BaseException as e:
@@ -1054,10 +1152,19 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
                 if dbtype is not None and \
                         (not exclude_types or dbtype not in exclude_types):
                     if translate:
+                        # TODO: this part won't work w/ the
+                        # expanded_parameters feature, e.g. for cx_oracle
+                        # quoted bound names
                         key = translate.get(key, key)
                     if not self.dialect.supports_unicode_binds:
                         key = self.dialect._encoder(key)[0]
-                    inputsizes[key] = dbtype
+                    if key in self._expanded_parameters:
+                        inputsizes.update(
+                            (expand_key, dbtype) for expand_key
+                            in self._expanded_parameters[key]
+                        )
+                    else:
+                        inputsizes[key] = dbtype
             try:
                 self.cursor.setinputsizes(**inputsizes)
             except BaseException as e: