add WhereTemplate to piccolo.columns.combination

[Jacky56]

Hello all,

dumb idea but let me present you a problem:
Assume that you have multiple metrics to filter by and you need to adjust your where statements according to the parameters given:

example:

async def list_posts(users: List[Users]=None, tags: List[Tags]=None, description: str=None) -> List[Posts]:
    query = (
        Posts.objects()
        .offset(123)
        .limit(123)
    )

    if users and tags and description:
        query = query.where(
            (Posts.users.is_in(users)) | (Posts.tags.is_in(tags)) | (Posts.description == description)
        )
    elif users and tags:
        query = query.where(
            (Posts.users.is_in(users)) | (Posts.tags.is_in(tags))
        )
    elif users and description:
        query = query.where(
            (Posts.users.is_in(users)) | (Posts.description == description)
        )
    elif tags and description:
        query = query.where(
            (Posts.tags.is_in(tags)) | (Posts.description == description)
        )
    elif users:
        query = query.where(Posts.users.is_in(users))
    elif tags:
        query = query.where(Posts.tags.is_in(tags))
    elif description:
        query = query.where(Posts.description == description)

    posts = await query
    return posts

Now I suggest a WhereTemplate, which effectively is a Where object but true, this will shrink down the conditional statements considering the filters are not and types

example:

async def list_posts(users: List[Users]=None, tags: List[Tags]=None, description: str=None) -> List[Posts]:
    query = (
        Posts.objects()
        .offset(123)
        .limit(123)
    )

    where = WhereTemplate()
    if users:
        where |= Posts.users.is_in(users) 
    if tags:
        where |= Posts.tags.is_in(tags)
    if description:
        where |= Posts.description == description
    
    posts = await query.where(where)
    return posts

Note that I am still relatively new to this Piccolo, so if there's a piccolo way of creating where statements, I am all ears.

[dantownsend]

@Jacky56 That's an interesting idea, thanks for sharing.

Your use case is something I've personally experienced a lot in my own projects. I hadn't considered using the |= operator. I'll have a think about it.