group by error with postgres and pomm orm - postgresql

Question

I want to execute the following SQL query :
SELECT date, COUNT(id_customers)
FROM event
WHERE event_id = 3
GROUP BY date
When I try this query in my database, it works perfectly. But in my code I get an error which I can't resolve.
I use symfony2 with the orm pomm. It's Postgresql.
Here is my code :
$sql = "SELECT e.date, COUNT(id_customers) FROM event e WHERE event_id = $* GROUP BY e.date";
return $this->query($sql, [$eventId])->extract();
Here is the error :
request.CRITICAL: Uncaught PHP Exception InvalidArgumentException:
"No such field 'id'. Existing fields are {date, count}"
at /home/vagrant/sourcefiles/vendor/pomm-project/model-manager/sources/lib/Model/FlexibleEntity/FlexibleContainer.php line 64
{"exception":" [object] (InvalidArgumentException(code: 0): No such field 'id'.
Existing fields are {date, count}
at /home/vagrant/sourcefiles/vendor/pomm-project/model-manager/sources/lib/Model/FlexibleEntity/FlexibleContainer.php:64)"} []
So I tried to had the id in my select, by I get this error :
request.CRITICAL: Uncaught PHP Exception
PommProject\Foundation\Exception\SqlException: "
SQL error state '42803' [ERROR] ==== ERROR: column "e.id" must appear in the GROUP BY clause or be used in an aggregate function LINE 1: SELECT e.id, e.date, COUNT(id_customers) FROM event e WHERE ... ^
==== «PREPARE === SELECT e.id, e.date, COUNT(id_customers) FROM event e WHERE event_id = $1 GROUP BY e.date ===»." at /home/vagrant/sourcefiles/vendor/pomm-project/foundation/sources/lib/Session/Connection.php line 327 {"exception":"[object] (PommProject\Foundation\Exception\SqlException(code: 0): \nSQL error state '42803' [ERROR]\n====\nERROR: column \"e.id\" must appear in the GROUP BY clause or be used in an aggregate function\nLINE 1: SELECT e.id, e.date, COUNT(id_customers) FROM event e WHERE ...\n ^\n\n====\n«PREPARE ===\nSELECT e.id, e.date, COUNT(id_customers) FROM event e WHERE event_id = $1 GROUP BY e.date\n ===». at /home/vagrant/sourcefiles/vendor/pomm-project/foundation/sources/lib/Session/Connection.php:327)"} []
The only thing that works is when I had the id in the group by, but this is not the result I want.
Someone can explain me why this is working in the database and not in the php ?

Answer 1

this is because you are fetching flexible entities without their primary key. There is an identity mapper behind the scene that ensure fetching twice the same entity will return the same instance.
In this case, you do not need to fetch entities (hence the extract after the query). So you can just use the QueryManager pooler to return converted arrays like the following:
$sql = "SELECT e.date, COUNT(id_customers) FROM event e WHERE event_id = $* GROUP BY e.date";
// Return an iterator that fetches converted arrays on demand:
return $this
->getSession()
->getQueryManager()
->query($sql, [$eventId])
;

Answer 2

i think its because the alias,
try this
$sql = "SELECT e.date, COUNT(e.id_customers) FROM event e WHERE event_id = $* GROUP BY e.date";
return $this->query($sql, [$eventId])->extract();

Answer 3

This is exactly how GROUP BY works in PostgreSQL:
When GROUP BY is present, it is not valid for the SELECT list
expressions to refer to ungrouped columns except within aggregate
functions, since there would be more than one possible value to return
for an ungrouped column.
It means that each field in your query either must be present in GROUP BY statement or handled by any of the aggregation functions. This is one of the differences between GROUP BY in MySQL and PostreSQL.
In other words you can add id at GROUP BY statement and do not worry about it ;)