pokedex/db/dependencies.py

   1 import sqlalchemy.sql.visitors as visitors
   2
   3 from pokedex.db.tables import metadata
   4
   5 # stolen from sqlalchemy.sql.util.sort_tables
   6 def compute_dependencies(tables):
   7     """Construct a reverse dependency graph for the given tables.
   8
   9     Returns a dict which maps a table to the list of tables which depend on it.
  10     """
  11     tables = list(tables)
  12     graph = {}
  13     def visit_foreign_key(fkey):
  14         if fkey.use_alter:
  15             return
  16         parent_table = fkey.column.table
  17         if parent_table in tables:
  18             child_table = fkey.parent.table
  19             if parent_table is not child_table:
  20                 graph.setdefault(parent_table, []).append(child_table)
  21
  22     for table in tables:
  23         visitors.traverse(table,
  24                           {'schema_visitor': True},
  25                           {'foreign_key': visit_foreign_key})
  26
  27         graph.setdefault(table, []).extend(table._extra_dependencies)
  28
  29     return graph
  30
  31 #: The dependency graph for pokedex.db.tables
  32 _pokedex_graph = compute_dependencies(metadata.tables.values())
  33
  34 def find_dependent_tables(tables, graph=None):
  35     """Recursively find all tables which depend on the given tables.
  36
  37     The returned set does not include the original tables.
  38     """
  39     if graph is None:
  40         graph = _pokedex_graph
  41     tables = list(tables)
  42     dependents = set()
  43     def add_dependents_of(table):
  44         for dependent_table in graph.get(table, []):
  45             if dependent_table not in dependents:
  46                 dependents.add(dependent_table)
  47                 add_dependents_of(dependent_table)
  48
  49     for table in tables:
  50         add_dependents_of(table)
  51
  52     dependents -= set(tables)
  53
  54     return dependents