veekun_pokedex/pokedex/db/load.py

"""CSV to database or vice versa."""
import csv
import pkg_resources
import sys

from sqlalchemy.orm.attributes import instrumentation_registry
import sqlalchemy.types

from pokedex.db import metadata
import pokedex.db.tables as tables


def _get_verbose_prints(verbose):
    """If `verbose` is true, returns two functions: one for printing a starting
    message, and the other for printing a success or failure message when
    finished.

    If `verbose` is false, returns two no-op functions.
    """

    if verbose:
        import sys
        def print_start(thing):
            # Truncate to 66 characters, leaving 10 characters for a success
            # or failure message
            truncated_thing = thing[0:66]

            # Also, space-pad to keep the cursor in a known column
            num_spaces = 66 - len(truncated_thing)

            print "%s...%s" % (truncated_thing, ' ' * num_spaces),
            sys.stdout.flush()

        def print_done(msg='ok'):
            print msg
            sys.stdout.flush()

        return print_start, print_done

    # Not verbose; return dummies
    def dummy(*args, **kwargs):
        pass

    return dummy, dummy


def load(session, directory=None, drop_tables=False, verbose=False):
    """Load data from CSV files into the given database session.

    Tables are created automatically.

    `session`
        SQLAlchemy session to use.

    `directory`
        Directory the CSV files reside in.  Defaults to the `pokedex` data
        directory.

    `drop_tables`
        If set to True, existing `pokedex`-related tables will be dropped.

    `verbose`
        If set to True, status messages will be printed to stdout.
    """

    # First take care of verbosity
    print_start, print_done = _get_verbose_prints(verbose)


    if not directory:
        directory = pkg_resources.resource_filename('pokedex', 'data/csv')

    # Drop all tables if requested
    if drop_tables:
        print_start('Dropping tables')
        metadata.drop_all()
        print_done()

    metadata.create_all()
    connection = session.connection()

    # Okay, run through the tables and actually load the data now
    for table_obj in metadata.sorted_tables:
        table_name = table_obj.name
        insert_stmt = table_obj.insert()

        print_start(table_name)

        try:
            csvfile = open("%s/%s.csv" % (directory, table_name), 'rb')
        except IOError:
            # File doesn't exist; don't load anything!
            print_done('missing?')
            continue

        reader = csv.reader(csvfile, lineterminator='\n')
        column_names = [unicode(column) for column in reader.next()]

        # Self-referential tables may contain rows with foreign keys of other
        # rows in the same table that do not yet exist.  Pull these out and add
        # them to the session last
        # ASSUMPTION: Self-referential tables have a single PK called "id"
        deferred_rows = []  # ( row referring to id, [foreign ids we need] )
        seen_ids = {}       # primary key we've seen => 1

        # Fetch foreign key columns that point at this table, if any
        self_ref_columns = []
        for column in table_obj.c:
            if any(_.references(table_obj) for _ in column.foreign_keys):
                self_ref_columns.append(column)

        new_rows = []
        def insert_and_commit():
            session.connection().execute(insert_stmt, new_rows)
            session.commit()
            new_rows[:] = []

        for csvs in reader:
            row_data = {}

            for column_name, value in zip(column_names, csvs):
                column = table_obj.c[column_name]
                if column.nullable and value == '':
                    # Empty string in a nullable column really means NULL
                    value = None
                elif isinstance(column.type, sqlalchemy.types.Boolean):
                    # Boolean values are stored as string values 0/1, but both
                    # of those evaluate as true; SQLA wants True/False
                    if value == '0':
                        value = False
                    else:
                        value = True
                else:
                    # Otherwise, unflatten from bytes
                    value = value.decode('utf-8')

                # nb: Dictionaries flattened with ** have to have string keys
                row_data[ str(column_name) ] = value

            # May need to stash this row and add it later if it refers to a
            # later row in this table
            if self_ref_columns:
                foreign_ids = [row_data[_.name] for _ in self_ref_columns]
                foreign_ids = [_ for _ in foreign_ids if _]  # remove NULL ids

                if not foreign_ids:
                    # NULL key.  Remember this row and add as usual.
                    seen_ids[row_data['id']] = 1

                elif all(_ in seen_ids for _ in foreign_ids):
                    # Non-NULL key we've already seen.  Remember it and commit
                    # so we know the old row exists when we add the new one
                    insert_and_commit()
                    seen_ids[row_data['id']] = 1

                else:
                    # Non-NULL future id.  Save this and insert it later!
                    deferred_rows.append((row_data, foreign_ids))
                    continue

            # Insert row!
            new_rows.append(row_data)

            # Remembering some zillion rows in the session consumes a lot of
            # RAM.  Let's not do that.  Commit every 1000 rows
            if len(new_rows) > 1000:
                insert_and_commit()

        insert_and_commit()

        # Attempt to add any spare rows we've collected
        for row_data, foreign_ids in deferred_rows:
            if not all(_ in seen_ids for _ in foreign_ids):
                # Could happen if row A refers to B which refers to C.
                # This is ridiculous and doesn't happen in my data so far
                raise ValueError("Too many levels of self-reference!  "
                                 "Row was: " + str(row))

            session.connection().execute(
                insert_stmt.values(**row_data)
            )
            seen_ids[row_data['id']] = 1
        session.commit()

        print_done()



def dump(session, directory=None, verbose=False):
    """Dumps the contents of a database to a set of CSV files.  Probably not
    useful to anyone besides a developer.

    `session`
        SQLAlchemy session to use.

    `directory`
        Directory the CSV files should be put in.  Defaults to the `pokedex`
        data directory.

    `verbose`
        If set to True, status messages will be printed to stdout.
    """

    # First take care of verbosity
    print_start, print_done = _get_verbose_prints(verbose)


    if not directory:
        directory = pkg_resources.resource_filename('pokedex', 'data/csv')

    for table_name in sorted(metadata.tables.keys()):
        print_start(table_name)
        table = metadata.tables[table_name]

        writer = csv.writer(open("%s/%s.csv" % (directory, table_name), 'wb'),
                            lineterminator='\n')
        columns = [col.name for col in table.columns]
        writer.writerow(columns)

        primary_key = table.primary_key
        for row in session.query(table).order_by(*primary_key).all():
            csvs = []
            for col in columns:
                # Convert Pythony values to something more universal
                val = getattr(row, col)
                if val == None:
                    val = ''
                elif val == True:
                    val = '1'
                elif val == False:
                    val = '0'
                else:
                    val = unicode(val).encode('utf-8')

                csvs.append(val)

            writer.writerow(csvs)

        print_done()