Bug: Aggregation `__bool__` returns True when empty

[CBroz1]

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Bug Report

Description

My intuition regarding projection and aggregation is that they return objects that will behave the same as tables. For an ordinary table, bool(Table) == len(Table) > 0, but this isn't the case for aggregations

Reproducibility

Include:

• OS Linux
• Python Version: 3.10
• MySQL Version: 8 latest
• MySQL Deployment Strategy local-docker
• DataJoint Version: 0.14.3
• Minimum number of steps to reliably reproduce the issue: see below
• Complete error stack as a result of evaluating the above steps: n/a

MWE

import datajoint as dj

schema = dj.schema("cbroz_temp")


@schema
class A(dj.Lookup):
    definition = """
    a_id: int
    """

    contents = [[i] for i in range(1, 3)]


@schema
class B(dj.Lookup):
    definition = """
    -> A
    b_id: int
    """

    contents = [(i, j) for i in range(1, 2) for j in range(4, 8)]


if __name__ == "__main__":
    has_entry = A & "a_id=1"
    no_entry = A & "a_id=3"
    print("Table with contents as bool: ", bool(has_entry)) # True
    print("Table without contents as bool: ", bool(no_entry)) # False
    aggr_has_entry = has_entry.aggr(B, b_id="COUNT(b_id)")
    aggr_no_entry = no_entry.aggr(B, b_id="COUNT(b_id)")
    print("Aggr table with contents as bool: ", bool(aggr_has_entry)) # True 
    print("Aggr table without contents as bool: ", bool(aggr_no_entry)) # True

Expected Behavior

I expected bool(Aggr) == len(Aggr) > 0

Screenshots

n/a

Additional Research and Context

• Checked existing issues
• Looked at git blame for the relevant code. PR #850 featured this commit, which chose to make the QueryExpression bool based on length and the Aggregation bool based on it being a valid selection - Is this related to evaluations during cascading delete?

[github-actions[bot]]

This issue is stale because it has been open for 45 days with no activity.

[github-actions[bot]]

This issue is stale because it has been open for 45 days with no activity.