Refactoring: Modularize CrateCompiler

By refactoring the SQLAlchemy 1.0-1.3 vs. 1.4 specialities of the
`CrateCompiler` (`visit_update` and `_get_crud_params`) into dedicated
modules, the new layout is more suitable for bringing in support for
SQLAlchemy 2.0.

src/crate/client/sqlalchemy/compat/core10.py

@@ -0,0 +1,256 @@
+# -*- coding: utf-8; -*-
+#
+# Licensed to CRATE Technology GmbH ("Crate") under one or more contributor
+# license agreements.  See the NOTICE file distributed with this work for
+# additional information regarding copyright ownership.  Crate licenses
+# this file to you under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.  You may
+# obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+# However, if you have executed another commercial license agreement
+# with Crate these terms will supersede the license and you may use the
+# software solely pursuant to the terms of the relevant commercial agreement.
+
+import sqlalchemy as sa
+from sqlalchemy.sql.crud import (REQUIRED, _create_bind_param,
+                                 _extend_values_for_multiparams,
+                                 _get_multitable_params,
+                                 _get_stmt_parameters_params,
+                                 _key_getters_for_crud_column, _scan_cols,
+                                 _scan_insert_from_select_cols)
+
+from crate.client.sqlalchemy.compiler import CrateCompiler
+
+
+class CrateCompilerSA10(CrateCompiler):
+
+    def visit_update(self, update_stmt, **kw):
+        """
+        used to compile <sql.expression.Update> expressions
+        Parts are taken from the SQLCompiler base class.
+        """
+
+        if not update_stmt.parameters and \
+                not hasattr(update_stmt, '_crate_specific'):
+            return super(CrateCompiler, self).visit_update(update_stmt, **kw)
+
+        self.isupdate = True
+
+        extra_froms = update_stmt._extra_froms
+
+        text = 'UPDATE '
+
+        if update_stmt._prefixes:
+            text += self._generate_prefixes(update_stmt,
+                                            update_stmt._prefixes, **kw)
+
+        table_text = self.update_tables_clause(update_stmt, update_stmt.table,
+                                               extra_froms, **kw)
+
+        dialect_hints = None
+        if update_stmt._hints:
+            dialect_hints, table_text = self._setup_crud_hints(
+                update_stmt, table_text
+            )
+
+        # [10] CrateDB patch.
+        crud_params = _get_crud_params(self, update_stmt, **kw)
+
+        text += table_text
+
+        text += ' SET '
+
+        # [10] CrateDB patch begin.
+        include_table = \
+            extra_froms and self.render_table_with_column_in_update_from
+
+        set_clauses = []
+
+        for k, v in crud_params:
+            clause = k._compiler_dispatch(self,
+                                          include_table=include_table) + \
+                ' = ' + v
+            set_clauses.append(clause)
+
+        for k, v in update_stmt.parameters.items():
+            if isinstance(k, str) and '[' in k:
+                bindparam = sa.sql.bindparam(k, v)
+                set_clauses.append(k + ' = ' + self.process(bindparam))
+
+        text += ', '.join(set_clauses)
+        # [10] CrateDB patch end.
+
+        if self.returning or update_stmt._returning:
+            if not self.returning:
+                self.returning = update_stmt._returning
+            if self.returning_precedes_values:
+                text += " " + self.returning_clause(
+                    update_stmt, self.returning)
+
+        if extra_froms:
+            extra_from_text = self.update_from_clause(
+                update_stmt,
+                update_stmt.table,
+                extra_froms,
+                dialect_hints,
+                **kw)
+            if extra_from_text:
+                text += " " + extra_from_text
+
+        if update_stmt._whereclause is not None:
+            t = self.process(update_stmt._whereclause)
+            if t:
+                text += " WHERE " + t
+
+        limit_clause = self.update_limit_clause(update_stmt)
+        if limit_clause:
+            text += " " + limit_clause
+
+        if self.returning and not self.returning_precedes_values:
+            text += " " + self.returning_clause(
+                update_stmt, self.returning)
+
+        return text
+
+
+def _get_crud_params(compiler, stmt, **kw):
+    """create a set of tuples representing column/string pairs for use
+    in an INSERT or UPDATE statement.
+
+    Also generates the Compiled object's postfetch, prefetch, and
+    returning column collections, used for default handling and ultimately
+    populating the ResultProxy's prefetch_cols() and postfetch_cols()
+    collections.
+
+    """
+
+    compiler.postfetch = []
+    compiler.insert_prefetch = []
+    compiler.update_prefetch = []
+    compiler.returning = []
+
+    # no parameters in the statement, no parameters in the
+    # compiled params - return binds for all columns
+    if compiler.column_keys is None and stmt.parameters is None:
+        return [
+            (c, _create_bind_param(compiler, c, None, required=True))
+            for c in stmt.table.columns
+        ]
+
+    if stmt._has_multi_parameters:
+        stmt_parameters = stmt.parameters[0]
+    else:
+        stmt_parameters = stmt.parameters
+
+    # getters - these are normally just column.key,
+    # but in the case of mysql multi-table update, the rules for
+    # .key must conditionally take tablename into account
+    (
+        _column_as_key,
+        _getattr_col_key,
+        _col_bind_name,
+    ) = _key_getters_for_crud_column(compiler, stmt)
+
+    # if we have statement parameters - set defaults in the
+    # compiled params
+    if compiler.column_keys is None:
+        parameters = {}
+    else:
+        parameters = dict(
+            (_column_as_key(key), REQUIRED)
+            for key in compiler.column_keys
+            if not stmt_parameters or key not in stmt_parameters
+        )
+
+    # create a list of column assignment clauses as tuples
+    values = []
+
+    if stmt_parameters is not None:
+        _get_stmt_parameters_params(
+            compiler, parameters, stmt_parameters, _column_as_key, values, kw
+        )
+
+    check_columns = {}
+
+    # special logic that only occurs for multi-table UPDATE
+    # statements
+    if compiler.isupdate and stmt._extra_froms and stmt_parameters:
+        _get_multitable_params(
+            compiler,
+            stmt,
+            stmt_parameters,
+            check_columns,
+            _col_bind_name,
+            _getattr_col_key,
+            values,
+            kw,
+        )
+
+    if compiler.isinsert and stmt.select_names:
+        _scan_insert_from_select_cols(
+            compiler,
+            stmt,
+            parameters,
+            _getattr_col_key,
+            _column_as_key,
+            _col_bind_name,
+            check_columns,
+            values,
+            kw,
+        )
+    else:
+        _scan_cols(
+            compiler,
+            stmt,
+            parameters,
+            _getattr_col_key,
+            _column_as_key,
+            _col_bind_name,
+            check_columns,
+            values,
+            kw,
+        )
+
+    # [10] CrateDB patch.
+    #
+    # This sanity check performed by SQLAlchemy currently needs to be
+    # deactivated in order to satisfy the rewriting logic of the CrateDB
+    # dialect in `rewrite_update` and `visit_update`.
+    #
+    # It can be quickly reproduced by activating this section and running the
+    # test cases::
+    #
+    #   ./bin/test -vvvv -t dict_test
+    #
+    # That croaks like::
+    #
+    #   sqlalchemy.exc.CompileError: Unconsumed column names: characters_name, data['nested']
+    #
+    # TODO: Investigate why this is actually happening and eventually mitigate
+    #       the root cause.
+    """
+    if parameters and stmt_parameters:
+        check = (
+            set(parameters)
+            .intersection(_column_as_key(k) for k in stmt_parameters)
+            .difference(check_columns)
+        )
+        if check:
+            raise exc.CompileError(
+                "Unconsumed column names: %s"
+                % (", ".join("%s" % c for c in check))
+            )
+    """
+
+    if stmt._has_multi_parameters:
+        values = _extend_values_for_multiparams(compiler, stmt, values, kw)
+
+    return values