fix: Aggregation and Union __bool__ always returning True

[dimitri-yatsenko]

Summary

Fixes the __bool__ method for Aggregation and Union classes which always returned True regardless of whether the query result was empty.

Problem

The __bool__ methods were missing .fetchone()[0]:

# Buggy code
def __bool__(self):
    return bool(self.connection.query("SELECT EXISTS({sql})".format(sql=self.make_sql())))

self.connection.query() returns a cursor object, and bool(cursor) is always True because the cursor object itself is truthy. The actual query result (0 or 1) was never fetched.

Fix

# Fixed code
def __bool__(self):
    return bool(
        self.connection.query(
            "SELECT EXISTS({sql})".format(sql=self.make_sql())
        ).fetchone()[0]
    )

Test

has_entry = A & "a_id=1"
no_entry = A & "a_id=3"

aggr_has_entry = has_entry.aggr(B, b_id="COUNT(b_id)")
aggr_no_entry = no_entry.aggr(B, b_id="COUNT(b_id)")

# Before fix: both True
# After fix: True, False (correct)
bool(aggr_has_entry)  # True
bool(aggr_no_entry)   # False

Closes

• Bug: Aggregation __bool__ returns True when empty #1234

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