CODEWITHSUNDEEP
pythonmysqlponyorm
Christian Macht
Christian Macht

Reputation: 466

Query with optional arguments using PonyORM

I'm building an API for a library of teambuilding games. The games have defined properties like type, size and length that I'm storing as many-to-many relationships. The model looks like this:

class Game(db.Entity):
    game_type = Set('Type')
    game_length = Set('Length')
    group_size = Set('GroupSize')
    ...

class Type(db.Entity):  # similar for Length, GroupSize
    game = Set(Game)
    short = Required(str)
    full = Required(str)

They are populated with different types/lengths/size values and then assigned to the different games. This works fine.

I had a hard time figuring out how to let users of the database query for e.g. two of these with the third not given. For example, I want all games with type=race AND size=medium but length=None.

I had built this before in SQL with subqueries and empty strings. This was my first working try with PonyORM:

def get_all_games(**kwargs):
    game_type = kwargs.get('game_type', None)
    group_size = kwargs.get('group_size', None)
    game_length = kwargs.get('game_length', None)

    query = select((g, gt, gs, gl) for g in Game
                                     for gt in g.game_type
                                       for gs in g.group_size
                                         for gl in g.game_length)

    if game_type:
        query = query.filter(lambda g, gt, gs, gl: gt.short == game_type)
    if group_size:
        query = query.filter(lambda g, gt, gs, gl: gs.short == group_size)
    if game_length:
        query = query.filter(lambda g, gt, gs, gl: gl.short == game_length)

    query = select(g for (g, gt, gs, gl) in query)

    result = []

    for g in query:
        this_game = get_game(g)
        result.append(this_game)

    return result

It seems overly complicated to me. Is there a way to do this without tuples packing and unpacking? Maybe with using the variables right away in the query without the if statements?

Upvotes: 2

Views: 275

Answers (1)

Alexander Kozlovsky
Alexander Kozlovsky

Reputation: 4849

You can use exists or in in filter. Also you can use attribute lifting to simplify complex joins:

query = Game.select()

if game_length:
    # example with exists
    query = query.filter(lambda g: exists(
        gl for gl in g.game_length
        if gl.min <= game_length and gl.max >= game_length))

if group_size:
    # example with in
    query = query.filter(lambda g: group_size in (
        gs.value for gs in g.group_sizes))

if game_type:
    # example with attribute lifting
    query = query.filter(lambda g: game_type in g.game_types.short)

Upvotes: 1

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