如何创建动态SQL查询

Question

I have a large sqlite table of 33k records (movies) . I want to give the user the ability to search in that table via filters . Each movie record has 10 fields : Actors, Directors, Runtime, Genre, Rating and few more . The only filters available for the user to use are people (Include Actors and Directors), Genre, Rating and Runtime .

The problem is that the user can use two filters or more, hence we don't really know which filter will be used . Filters values are passed via an HTTP req to the server which process it and create an SQL query based on filters to execute on the db .

What I can't understand is how can I create an SQL query if I don't know which filters will be used ? Because only used filters will be sent to the server .

Basically I want to find a way to create an SQL query based on sent filters by each users .

Answer 1

If you're given a list of filters, you can just apply Query.filter_by() or Query.filter() over and over:

filters = [
    ('rating', 3),
    ('runtime', 90),
    ('genre', 'documentary')
]

query = session.query(Movie)

for column, value in filters:
    # Make sure `column` and `value` are legal values!

    query = query.filter_by(**{column: value})

Since the query is evaluated only at the end, you're essentially doing:

query = query.filter_by(...).filter_by(...) ...

In the last line, filter_by(**{column: value}) is notation for filter_by(value_of_column_variable=value) .