Filling a Collection with alsoFetch: still materializes Proxies...

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Nov 4, 2020, 2:09:41 AM11/4/20
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Hi there,

I have this weird thing I don't understand. For a GUI component I issue a query like this (very simplified):

q := SimpleQuery read: Garage where: [:g| g cars anySatisfy: [:c| color = 'silver']].
q alsoFetch: [:g| g car wheels asOuterJoin].

myCarCollection := self session execute: q.

Obviously, I am talking about a OneToManyRelationship here.

So once this collection of cars is read from the database, it is displayed in a list to the user. IN the list I want to display whether the car has wheels or not.

Now to the "funny" effect. Each car will then issue an SQL statement like this whenever the getter #cars of a Garage is accessed:

FROM WHEEL WHERE CAR_ID = "the id of a car"

So it seems that even though my initial search/query joins the Garage, Car and Wheel table, the cars will hold a Proxy in their wheels inst var.

In our not so simple productive case, this means that some lists take a long time to render because it issues a few hundred SQL statements for data that has already been read in the first query.

I already tried tried #shouldProxy: false in the OneToManyMapping for the car's wheels attribute, but to no avail. Even adding the alsoFetch: to the Garage's #cars mapping doesn't avoid these extra SQLs. (and it may be a tricky optimization that strikes back whenever the wheels of cars in a garage aren't needed....)

Any ideas what I can do?


Thomas Brodt

Nov 4, 2020, 5:17:45 AM11/4/20

Your query fetches Garages and you do an alsoFetch: of wheels, but not of the cars. Maybe you have a retrieve: [:g | g car] that isn't mentioned in the mail, that would change the query output to cars. If you add

q alsoFetch: [:g | g car "or cars?"]

to the query (not to the mapping) does this help?

So you should have

q := SimpleQuery read: Garage where: [:g| g cars anySatisfy: [:c| color = 'silver']].
q alsoFetch: [:g | g cars]
q alsoFetch: [:g | g car wheels asOuterJoin].


Freundliche Grüsse
Thomas Brodt

porabo Consulting GmbH
Thomas Brodt, Diplom-Informatiker
Leiter Entwicklung

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Nov 5, 2020, 1:41:42 AM11/5/20
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Hi Thomas,

thanks for you suggestion. I tried

q := SimpleQuery read: Garage where: [:g| g cars anySatisfy: [:c| color = 'silver']].
q alsoFetch: [:g | g cars]
q alsoFetch: [:g | g cars wheels asOuterJoin].

but the list rendering still sends out a single select for the wheels of each car just milliseconds later.

This is strange, because I don't see this behaviour in other places where we use #alsoFetch: in Queries. It is a very efficient performance booster under (whatever different) circumstances.


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