Query identity operation

[Leon Albrecht]

Hey everyone,

I'm running a website, that uses a search bar, and to parse said search bar, I "and" together multiple queries in a loop,

but to start of I need a Identity-Query, that does nothing and return everything.

There are solutions to create one, but they aren't free and do not look good or intuitive.

So I suggest adding a Identity-Query object, which gets discarded by the optimizer during the SQL generation stage.

Leon

PS:

Just using multiple filters wont work, because they always use the original data set and unify all results at the end.

PPS:

An issue that occurred me is that "and"-ing together queries may cause the results to be duplicate.

[Adam Johnson]

How is this different from QuerySet.all() ? Can you give a code example of what you'd imagine this API doing?

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Adam

[Leon Albrecht]

OK no clue, why it didn't send my answer from 15min ago but,

I will give an example similar to my exact use case:

...

search_query = request.GET.get("q", "").lower() # string of features the user searches for separated by whitespaces

complete_query = ~Q(pk__in=[]) # this should be something like Q.ident()

for query in search_query.split():

  complete_query &= (

    Q(author__first_name__icontains = query) |

    Q(author__last_name__icontains = query) |

    Q(year = query if query.isdigit() else  -1) |

    Q(title__icontains = query)

    )

books= Book.objects.filter(complete_query).distinct() # distinct() is fo rthe issue described in the PPS

... # render page with relevant books

----

Leon

PS:

Does this service allow inline html, could have been the reason why it wasn't send or it just takes a while and I'm to imaptient

[Leon Albrecht]

Ok, I will follow with exemplary code similar to the one i use:

<code>

...

searchquery = request.GET["q"]

complete_query = ~Q(pk__in=[])  # this should be something like Q.ident()

            for query in search_query.split():

                complete_query &= (

                    Q(autor__first_name__icontains=query) |

                    Q(author__last_name__icontains=query) |

                    Q(title__icontains=query) |

                    Q(year=int(query) if query.isdigit() else -1)

                )

            books = Book.obejects.filter(complete_query).distinct() # the distinct is for the issue described in the PPS

... # render page with the filtered books

</code>

in the Example the searchquery is a string of features seperated by whitespaces the user wants to search for and the Book model is similar to the one described in the django tutorials, if I remember them right.

[Mariusz Felisiak]

complete_query = ~Q(pk__in=[])  # this should be something like Q.ident()

You can use `complete_query = Q()`. Also, this mailing list is for discussing the development of Django itself, not for support using Django.

 

Best,
Mariusz

[Adam Johnson]

I saw that Q() with no arguments is not documented, so I've made a PR to add a sentence covering it: https://github.com/django/django/pull/13798 .

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Adam

[Ken Whitesell]

A couple questions came to mind if we're going to document this as "official behavior":

1. This also appears to be true for filter. Would the same clarification be appropriate there?

2. I don't see any tests validating the behavior for either Q or filter, should there be?

Ken

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[Adam Johnson]

1. Sure, pushed a commit

2. Tests: https://github.com/adamchainz/django/blob/72ce349bb283910b8c4d6a6e0f2250055b5bffb5/tests/queries/test_q.py#L6-L9

Please leave PR-specific feedback on GitHub in future :)

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Adam