# $Id: database.krb 4dca5ad0f397 2010-03-10 mtnyogi $
#
# Copyright © 2008 Bruce Frederiksen
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.


#
# This logic adds inheritance to the database tables.  This means that when
# table A includes a foreign key to table B, all of the columns in table B are
# inherited by table A and can be used as if they appeared directly in table A.
# The logic will automatically add the necessary joins from table A to table B.
# This inheritance goes on any number of levels, so columns inherited by
# table B are also included in table A.
#
# This example is simplified in the following ways:
#    - it is assumed that the primary key to all tables is called 'id'.
#    - it is assumed that all foreign keys linking to table 'B' are called
#      'B_id'.
#    - functions and operators are not supported (in the 'where' or 'select'
#      clause).
#        - thus no aggregation is possible; so no need for a "group by" clause
#          which would otherwise be added automatically.
#    - updates are not supported (insert, update, delete).
#    - column_name qualification is not supported to disambiguate between
#      multiple columns being inherited with the same name.


# get_data($starting_tables, $needed_data) taking(db_cursor, starting_keys)
#
# This is the top-level goal to generate a plan to retrieve a set of data.
#   Input goal arguments:
#     $starting_tables      - a tuple of table_names that keys will be
#                             provided for when the plan is called (e.g.,
#                             ('movie',)).
#     $needed_data          - a tuple of data descriptors describing the data
#                             that should be returned (as a dict) from
#                             executing the plan.  Each data descriptor is one
#                             of the following:
#                                column_name
#                                  -- binds a single (ie, unique) value to
#                                     column_name
#                                (name, (option...), needed_data...)
#                                  -- binds a tuple of dictionaries to name
#                                  -- an option is:
#                                       ('linked_to' table_name)
#                                           -- table_name is the "1" table in
#                                              the many_to_1 link
#                                       ('order_by' 'asc'|'desc'|column_name...)
#                                  -- needed_data can only be a column_name at
#                                     this point (no nested multirow queries).
#   plan arguments:
#     db_cursor             - an open cursor to the database.
#     starting_keys         - a dict mapping the table_names in
#                             $starting_tables to their key values (e.g.,
#                             {'movie': 4}).
#   plan return:
#     The plan returns a dict mapping the names in $needed_data to their
#     values from the database.
get_data
    use get_data($starting_tables, $needed_data)
        taking(db_cursor, starting_keys)
    when
        #python print("get_data: starting_tables: %s" % str($starting_tables))
        #python print("get_data: needed_data: %s" % str($needed_data))
        !parse_needed_data($starting_tables, $needed_data,
                           $multi_plans, $unique_queries)
        !process_unique_queries($unique_queries)
            ans = {}
            $$(db_cursor, starting_keys, ans)
    with
        for row_name, plan in $multi_plans:
            ans[row_name] = plan(db_cursor, starting_keys)
        return ans

# parse_needed_data($starting_tables, $needed_data,
#                   $multi_plans, $unique_queries)
#
# This parses all of the $needed_data and produces two outputs: one for the
# multi_row data, and the other for the unique data.
#   Input goal arguments:
#     $starting_tables      - a tuple of table_names that keys will be
#                             provided for when the plan is called (e.g.,
#                             ('movie',)).
#     $needed_data          - a tuple of data descriptors describing the data
#                             that should be returned (as a dict) from
#                             executing the plan.  Each data descriptor is one
#                             of the following:
#                                column_name
#                                  -- binds a single (ie, unique) value to
#                                     column_name
#                                (name, (option...), needed_data...)
#                                  -- binds a tuple of dictionaries to name
#                                  -- an option is:
#                                       ('linked_to' table_name)
#                                           -- table_name is the "1" table in
#                                              the many_to_1 link
#                                       ('order_by' 'asc'|'desc'|column_name...)
#                                  -- needed_data can only be a column_name at
#                                     this point (no nested multirow queries).
#   Output goal arguments:
#     $multi_plans              - A tuple of two-tuples; one for each request
#                                 for multi-row data.  Each two-tuple has: 
#                                   row_name
#                                     - the key to set in the top-level dict.
#                                   plan
#                                     - a function taking (db_cursor,
#                                       starting_keys)
#     $unique_queries           - A tuple of three-tuples; one for each
#                                 request for a unique data value.  Each
#                                 three-tuple has:
#                                   from clause
#                                     - a tuple starting with table_name_a
#                                       followed by:
#                                         (table_name_b, from_table,
#                                          from_columns, b_columns)...
#                                   select clause
#                                     - a column_name in the last table of the
#                                       from clause
#                                   name binding
#                                     - the key in the resulting dict
# No plan is returned.
parse_needed_data
    use parse_needed_data($starting_tables, $needed_data,
                          $multi_plans, $unique_queries)
    when
        #python print("parse_needed_data(%s, %s, _, _)" %
        #                ($starting_tables, $needed_data))

        # Note difference between multi_plans and $multi_plans!
        python multi_plans = []
        python unique_queries = []

        forall
            $needed_element in $needed_data
        require
            parse_needed_element($starting_tables, $needed_element,
                                 $multi_plan, $unique_queries1)
            python if $multi_plan: multi_plans.append($multi_plan)
            python if $unique_queries1: unique_queries.append($unique_queries1)
        $multi_plans = tuple(multi_plans)
        $unique_queries = tuple(unique_queries)


# parse_needed_element($starting_tables, $needed_element,
#                      $multi_plan, $unique_query)
#
# This processes one element in $needed_data.
#   Input goal arguments:
#     $starting_tables      - a tuple of table_names that keys will be
#                             provided for when the plan is called (e.g.,
#                             ('movie',)).
#     $needed_element       - one of the following:
#                                column_name
#                                  -- binds a single (ie, unique) value to
#                                     column_name
#                                (name, (option...), needed_data...)
#                                  -- binds a tuple of dictionaries to name
#                                  -- an option is:
#                                       ('linked_to' table_name)
#                                           -- table_name is the "1" table in
#                                              the many_to_1 link
#                                       ('order_by' 'asc'|'desc'|column_name...)
#                                  -- needed_data can only be a column_name at
#                                     this point (no nested multirow queries).
#   Output goal arguments:
#     $multi_plan               - a two-tuple: (row_name, plan), or None
#                                   row_name
#                                     - the key to set in the top-level dict.
#                                   plan
#                                     - a function taking (db_cursor,
#                                       starting_keys)
#     $unique_query             - This element is a three-tuple or None:
#                                   from clause
#                                     - a tuple starting with table_name_a
#                                       followed by:
#                                         (table_name_b, from_table,
#                                          from_columns, b_columns)...
#                                   select clause
#                                     - a column_name in the last table of the
#                                       from clause
#                                   name binding
#                                     - the key in the resulting dict
# No plan is returned.
parse_needed_element_multi
    use parse_needed_element($starting_tables,
                             ($row_name, $options, *$multi_data),
                             ($row_name, $plan),
                             None)
    when
        # Multi-row request.
        special.claim_goal()
        get_multi($starting_tables, $options, $multi_data, $plan)

parse_needed_element_unique
    use parse_needed_element($starting_tables, $unique_data, None, $unique_out)
    when
        # Single-row (unique) request.
        get_unique($starting_tables, $unique_data, $unique_out)

# get_unique($starting_tables, $column, $unique_query)
#
# This processes one column in $needed_data.
#   Input goal arguments:
#     $starting_tables      - a tuple of table_names that keys will be
#                             provided for when the plan is called (e.g.,
#                             ('movie',)).
#     $column               - the desired column_name
#   Output goal arguments:
#     $unique_query         - A three-tuple:
#                                from clause
#                                  - a tuple starting with table_name_a
#                                    followed by:
#                                      (table_name_b, from_table,
#                                       from_columns, b_columns)...
#                                select clause
#                                  - a column_name in the last table of the
#                                    from clause
#                                name binding
#                                  - the key in the resulting dict
# No plan is returned.
get_unique_direct
    use get_unique($starting_tables, $column, (($table), $column, $column))
    when
        # This handles the case where $column is directly in one of the
        # $starting_tables.
        lookup_column($column, $starting_tables, $table)
        special.claim_goal()
        # lookup_column sets $table to None if there were multiple matches...
        # (which is an error and should cause get_unique to fail).
        check $table

get_unique_indirect
    use get_unique($starting_tables, $column, ($from_clause, $column, $column))
    when
        # This handles the case where $column is inherited into one of the
        # $starting_tables.
        lookup_indirect(1, $column, $starting_tables, $from_clause)

# lookup_column($column, $starting_tables, $table)
#
# This figures out which unique table within $starting_tables contains $column.
#
# This succeeds with None, after printing an error message, if $column appears
# in more than one $table within $starting_tables.  This is done so that the
# invoking goal does not try to find inherited columns in this situation.
#
# It fails if none of the tables in $starting_tables contain $column.
#
#   Input goal arguments:
#     $column               - The desired column_name.
#     $starting_tables      - A tuple of table_names.
#   Output goal arguments:
#     $table                - The table_name of the table in $starting_tables
#                             containing $column, or None.
# No plan is returned.
lookup_column
    use lookup_column($column, $starting_tables, $table)
    when
        # Find all of the tables in $starting_tables that have $column.
        find_columns($column, $starting_tables, $tables)
        unique_table($column, $tables, $table)

# find_columns($column, $tables_in, $matching_tables)
#
# Produces a list of the table in $tables_in that directly contain $column.
#   Input goal arguments:
#     $column               - The column_name to look for.
#     $tables_in            - A tuple of table_names.
#   Output goal arguments:
#     $matching_tables      - A tuple of the table_names in $tables_in that
#                             directly contain $column.
# No plan is returned.
find_columns
    use find_columns($column, $tables_in, $matching_tables)
    when
        python matching_tables = []
        forall
            $table in $tables_in
            schema.column($table, $column, $_, $_, $_, $_, $_)
            python matching_tables.append($table)
        $matching_tables = tuple(matching_tables)

# unique_table($column, $table_list, $table)
#
# This checks to see if $table_list contains only one table.
#
# If so, it returns it.
# If $table_list is empty, it fails.
# If $table_list has more than one table, it prints an error message and
# succeeds with $table set to None.
#
#   Input goal arguments:
#     $column               - The column_name to use in the error message.
#     $table_list           - A tuple of table_names.
#   Output goal arguments:
#     $table                - The table_name of the only table in $table_list,
#                             or None.
# No plan is returned.
unique_table_success
    use unique_table($_, ($table), $table)
    when
        # A single table was found: Success!
        special.claim_goal()

unique_table_not_found
    use unique_table($_, (), $_)
    when
        # No tables were found: cause the unique_table goal to fail!
        special.claim_goal()
        check False

unique_table_dups
    use unique_table($column, $tables, None)
    when
        # Multiple tables were found!
        # Print error message:
        python print("duplicate column %s, found in %s" % ($column, $tables))
        # Then succeed with None to flag the problem...

# lookup_indirect($depth, $column, $starting_tables, $from_clause)
#
# This implements a depth first search of the tables inherited by the tables
# in $starting_tables looking for $column.  It calls itself recursively to
# search at ever greater $depth values (starting with 1).
#
# It will fail if the $column can't be found, or if the $column exists in more
# than one inherited table at the same $depth when first encountered.  (It's
# OK if the first encounter is unique, but there are more $columns at a
# greater depth).
#
# No plan is returned.
lookup_indirect
    use lookup_indirect($depth, $column, $starting_tables, $from_clause)
    when
        #python print("lookup_indirect: "
        #                "find_at_depth(%s, %s, %s, _, _)" %
        #                ($depth, $column, $starting_tables))
        !find_at_depth($depth, $column, $starting_tables,
                       $got_depth, $from_clauses)
        #python print("lookup_indirect: "
        #                "lookup_indirect2(%s, %s, %s, %s, %s, _)" %
        #                ($depth, $column, $starting_tables, $got_depth,
        #                 $tables))
        lookup_indirect2($depth, $column, $starting_tables, $got_depth,
                         $from_clauses, $from_clause)


# lookup_indirect2($depth, $column, $starting_tables, $got_depth, $from_clauses,
#                  $from_clause)
#
# This finishes the job for lookup_indirect after find_at_depth has looked for
# $column at $depth.  $got_depth is a bool indicating whether there were any
# inherited tables at $depth.  This is how lookup_indirect2 knows when to stop
# searching at greater depths.
#
# No plan is returned.
lookup_indirect2_success
    # $column found in one table.  Success!
    use lookup_indirect2($_depth, $_column, $_starting_tables, $_got_depth,
                         ($from_clause), $from_clause)
    when
        # Found it!
        special.claim_goal()

lookup_indirect2_next_depth
    # $column not found, but there are still tables at this $depth.
    # Try the next higher $depth...
    use lookup_indirect2($depth, $column, $starting_tables, True, (),
                         $from_clause)
    when
        # $column not found, but the inherited tables haven't hit $depth yet!
        special.claim_goal()
        $depth2 = $depth + 1
        lookup_indirect($depth2, $column, $starting_tables, $from_clause)

lookup_indirect2_dups
    # We're using $got_depth of True here so that we don't match empty $froms.
    # We can do this because $got_depth must be True if there are any $froms.
    # If $got_depth is False, let lookup_indirect2 fail silently...
    use lookup_indirect2($_depth, $column, $_starting_tables, True, $froms, $_)
    when
        python print("duplicate tables for %s: %s" %
                         ($column, tuple(from_[0] for from_ in $froms)))
        check False

# find_at_depth($depth, $column, $starting_tables, $got_depth, $from_clauses)
#
# This looks for $column at an inheritance depth of $depth from each table in
# $starting_tables.  It returns $got_depth of True if any tables were found at
# this depth and the $from_clauses of all the matches.
#
# No plan is returned.
find_at_depth
    use find_at_depth($depth, $column, $starting_tables,
                      $got_depth, $from_clauses)
    when
        python got_depth = False
        python from_clauses = []
        forall
            $table in $starting_tables
        require
            ($got_depth1, $from) = find_at_depth1(engine, $depth, $column,
                                                  $table)
            python got_depth = got_depth or $got_depth1
            python from_clauses.extend($from)
        $got_depth = got_depth
        $from_clauses = tuple(from_clauses)

# process_unique_queries($unique_queries) taking(db_cursor, starting_keys, dict)
#
# This groups queries from a common root table into one sql select statement
# to minimize the number of sql statements issued to the database.  It does
# this by:
#    1. Taking the first item in $unique_queries
#    2. Going through the rest of the items in $unique_queries sorting out
#       those that can be combined and those that can't.
#    3. For all of the combined queries it generates a single sql select
#       statement.
#    4. Then it repeats the process on those queries that can't be combined
#       until no queries remain.
#
# It returns a plan that will execute these sql statements and populate a dict
# with the answers.
process_unique_queries_done
    # All done!
    use process_unique_queries(()) taking(db_cursor, starting_keys, dict)
    with
        pass

process_unique_queries_step
    use process_unique_queries((($from, $select, $key), *$rest))
        taking(db_cursor, starting_keys, dict)
    when
        $select2 = "%s.%s" % (($from[0] if len($from) == 1 else $from[-1][0]),
                              $select)
        #python print("process_unique_queries_step: "
        #             "combine_queries(%s, %s, _, _)" %
        #                (($from, ($select2,), ($key,)), $rest))
        !combine_queries(($from, ($select2), ($key)), $rest, $combined_query,
                         $uncombined_queries)
        #python print("process_unique_queries_step: combined_query is: %s" %
        #                str($combined_query))
        !run_query($combined_query)
            $$(db_cursor, starting_keys, dict)
        !process_unique_queries($uncombined_queries)
            $$(db_cursor, starting_keys, dict)

# combine_queries($unique_query, $rest_unique_queries,
#                 $combined_query, $uncombined_queries)
#
# This combines $unique_query with as many queries in $rest_unique_queries as
# it can.  The combined query is returned in $combined_query and the
# uncombined queries are returned as a tuple in $uncombined_queries.
#
# No plan is returned.
combine_queries_done_n
    # All done!
    use combine_queries($query, (), $query, ())

combine_queries_match_n
    # The next query in $rest_unique_queries can be combined!
    use combine_queries((($table1, *$joins1), $select_columns1, $dict_keys1),
                        ((($table1, *$joins2), $select_column2, $dict_key2),
                         *$rest),
                        $combined_query,
                        $uncombined_queries)
    when
        special.claim_goal()
        #python print("merge_joins(%s, %s, $merged_join)" % 
        #                ($joins1, $joins2))
        !merge_joins($joins1, $joins2, $merged_join)
        $select2 = "%s.%s" % (($table1 if not $joins2 else $joins2[-1][0]),
                              $select_column2)
        !combine_queries((($table1, *$merged_join),
                          ($select2, *$select_columns1),
                          ($dict_key2, *$dict_keys1)),
                         $rest, $combined_query, $uncombined_queries)

combine_queries_match
    # The next query in $rest_unique_queries can not be combined...
    use combine_queries($query1, ($uncombined_query1, *$rest), $combined_query,
                        ($uncombined_query1, *$uncombined_queries))
    when
        !combine_queries($query1, $rest, $combined_query, $uncombined_queries)

# merge_joins($joins1, $joins2, $merged_join)
#
# Merges two join clauses into one.  It does this by determining how many of
# the leading tables match (if any) and then appending the unmatched tail of
# the second join clause to the end of the first join clause.
#
# This goal should never fail.
#
# Examples:
#   merge_joins((table1, table2, table3), (table1, table2, table4),
#               (table1, table2, table3, table4))
#
#   merge_joins((table1, table2), (table3, table4),
#               (table1, table2, table3, table4))
#
#   merge_joins((table1, table2, table3), (table1, table2),
#               (table1, table2, table3))
#
# No plan is returned.
merge_joins_match
    # Merge joins with the same first table by merging the rest of the joins
    # in each clause. 
    use merge_joins(($first_join, *$rest_joins1), ($first_join, *$rest_joins2),
                    ($first_join, *$merged_joins))
    when
        special.claim_goal()
        merge_joins($rest_joins1, $rest_joins2, $merged_joins)

merge_joins_no_match
    # Merge joins with different first tables by concatenating the join
    # clauses.
    use merge_joins($joins1, $joins2, $merged_joins)
    when
        $merged_joins = $joins1 + $joins2

# run_query($combined_query) taking(db_cursor, starting_keys, dict)
#
# This constructs a sql select statement for $combined_query and returns a
# plan to run that select statement and populate a dict with the results.
run_query
    use run_query((($table, *$joins), $select_columns, $dict_keys))
        taking(db_cursor, starting_keys, dict)
    when
        #python print("make_from_clause(%s, %s, $from_clause)" %
        #                ($table, $joins))
        !make_from_clause($table, $joins, $from_clause)
        command_parameters($param, id, $param_fn)
        $sql_command = "select %s\n  from %s\n where %s.id = %s" % \
                           (', '.join($select_columns), $from_clause, $table,
                            $param)
    with
        db_cursor.execute($sql_command, $param_fn(starting_keys[$table]))
        if db_cursor.rowcount != -1 and db_cursor.rowcount is not None:
            assert db_cursor.rowcount == 1, \
                'expected unique row, got %d rows from "%s"' % \
                  (db_cursor.rowcount, $sql_command)
            dict.update(zip($dict_keys, db_cursor.fetchone()))
        else:
            row = db_cursor.fetchone()
            assert row is not None, \
                'expected unique row, got 0 rows from "%s"' % ($sql_command,)
            dict.update(zip($dict_keys, row))
            assert db_cursor.fetchone() is None, \
                'expected unique row, got >1 rows from "%s"' % ($sql_command,)

# make_from_clause($table, $joins, $from_clause)
#
# Creates the $from_clause for a sql select statement (as a string) starting
# with $table and including the $joins.
#
# No plan is returned.
make_from_clause
    use make_from_clause($table, $joins, $from_clause)
    when
        python from_clause = $table
        forall
            $join in $joins
        require
            ($table2, $from_table, $from_cols, $to_cols) = $join
            python from_clause += "\n           inner join %s on (%s)" % \
                       ($table2,
                        ' and '.join("%s.%s = %s.%s" %
                                        ($from_table, from_col, $table2, to_col)
                                     for from_col, to_col
                                     in zip($from_cols, $to_cols)))
        $from_clause = from_clause

# get_multi($starting_tables, $options, $multi_data, $plan)
#
# This creates a $plan for retrieving the multi-row $multi_data starting from
# $starting_tables with any indicated $options.
#   Input goal arguments:
#     $starting_tables      - a tuple of table_names that keys will be
#                             provided for when the plan is called (e.g.,
#                             ('movie',)).
#     $options              - a tuple of options.  Currently, only two options
#                             are supported:
#                               ('linked_to', table_name)
#                               ('order_by', 'asc'|'desc'|column_name...)
#     $multi_data           - can only be a tuple of column_names at this point
#                             (no nested multirow queries).
#   Output goal arguments:
#     $plan                 - a function taking (db_cursor, starting_keys) that
#                             will return a tuple of dicts (one per row in the
#                             select result).
#
# No plan is attached to the goal.  Instead, it is returned in $plan.
get_multi
    use get_multi($starting_tables, $options, $multi_data, $plan)
    when
        $linked_to = dict($options).get('linked_to')
        $order_by = dict($options).get('order_by')
        get_multi2($starting_tables, $multi_data, $linked_to, $order_by, $plan)

# get_multi2($starting_tables, $multi_data, $linked_to, $order_by, $plan)
#
# This is a continuation of the get_multi goal (above) with the options pulled
# out separately.
#
# No plan is attached to the goal.  Instead, it is returned in $plan.
get_multi2_no_linked_to
    use get_multi2($starting_tables, $multi_data, None, $order_by, $plan)
    when
        special.claim_goal()
        # Try each $unique_table in $starting_tables to find one that
        # find_multi_from_unique likes.
        # FIX: This should check for duplicates (ambiguous specification)!
        $unique_table in $starting_tables
        find_multi_from_unique($unique_table, $multi_data, $order_by, $plan)

get_multi2_linked_to
    use get_multi2($starting_tables, $multi_data, $linked_to, $order_by,
                   $plan)
    when
        # FIX: This should allow $linked_to to be an inherited table
        #      Or should we allow specifying the multi-row table rather than
        #      (in addition to?) the linked_to table?
        check $linked_to in $starting_tables
        find_multi_from_unique($linked_to, $multi_data, $order_by, $plan)

# find_multi_from_unique($unique_table, $multi_data, $order_by, $plan)
#
# Finds a many-to-1 relationship between some table X (as the "many" end of
# the relationship) and $unique_table (as the "1" end of the relationship) and
# then creates a plan to retrieve the columns specified in $multi_data from
# that table X.
#
# No plan is attached to the goal.  Instead, it is returned in $plan.
find_multi_from_unique
    use find_multi_from_unique($unique_table, $multi_data, $order_by, $plan)
    when
        # FIX: This should check for duplicate possibilities (duplicate
        #      $multi_tables)!
        schema.many_to_1($multi_table, $unique_table, ($multi_link_column), $_)
        parse_needed_data(($multi_table), $multi_data, (), $unique_queries)
        process_multi_queries($unique_queries, $combined_query)
        run_multi_query($unique_table, $combined_query, $multi_link_column,
                        $order_by) as $plan

# process_multi_queries($unique_queries, $combined_query)
#
# This combines the $unique_queries into a single $combined_query.
#
# No plan is returned.
process_multi_queries_none
    use process_multi_queries((), ())

process_multi_queries_some
    use process_multi_queries((($from, $select, $key), *$rest), $combined_query)
    when
        $select2 = "%s.%s" % (($from[0] if len($from) == 1 else $from[-1][0]),
                              $select)
        combine_queries(($from, ($select2), ($key)), $rest, $combined_query, ())

# run_multi_query($unique_table, $combined_query, $multi_link_column, $order_by)
# taking (db_cursor, starting_keys)
#
# This creates a sql select statement to retrieve multi-row data.  The first
# table in $combined_query must link to $unique_table by $multi_link_column to
# generate the multiple rows.
#
# It generates a plan to execute this sql select statement and create a tuple
# of dicts, one per row in the select response.
#
# The plan returns a tuple of dictionaries
run_multi_query
    use run_multi_query($unique_table,
                        (($table1, *$joins1), $select_columns, $dict_keys),
                        $multi_link_column, $order_by) \
        taking (db_cursor, starting_keys)
    when
        !make_from_clause($table1, $joins1, $from_clause)
        command_parameters($param, id, $param_fn)
        # FIX: Add order_by
        $sql_command = "select %s\n  from %s\n where %s.%s = %s" % \
                           (', '.join($select_columns), $from_clause,
                            $table1, $multi_link_column, $param)
    with
        db_cursor.execute($sql_command, $param_fn(starting_keys[$unique_table]))
        return tuple(dict(zip($dict_keys, row)) for row in db_cursor.fetchall())

format_params
    use command_parameters('%s', $_param_name, $param_fn)
    when
        schema.paramstyle(format)
        $param_fn = lambda param, prev_params = (): prev_params + (param,)

qmark_params
    use command_parameters('?', $_param_name, $param_fn)
    when
        schema.paramstyle(qmark)
        $param_fn = lambda param, prev_params = (): prev_params + (param,)

bc_extras
    from pyke import goal

    links_to = \
      goal.compile('schema.links_to($depth, $table, $to_table, $joins)')

    column_lookup = \
      goal.compile('schema.column($to_table, $column, $_, $_, $_, $_, $_)')

    def find_at_depth1(engine, depth, column, table):
        got_depth = False
        ans_joins = []
        with links_to.prove(engine, depth=depth, table=table) as gen1:
            for vars, bogus_plan1 in gen1:
                to_table, joins = vars['to_table'], vars['joins']
                got_depth = True
                with column_lookup.prove(engine,
                                         to_table=to_table, column=column) \
                  as gen2:
                    for bogus_vars, bogus_plan1 in gen2:
                        ans_joins.append((table,) + joins)
        return got_depth, tuple(ans_joins)

