Eager loading by default possible ?

[Jan van de Sandt]

Hello list,

With a query you can use the alsoFetch:  method to "eager load" related objects. Is it possible to specify a mapping so that Glorp does this by default?

My Model is something like this:

Class A ----(*)--> Class B ----(1)--> Class C

Class A has a collection of B instances and each B instance refers to exactly one C instance. What I would like to have is that when Glorp loads the the collection of B instances for an A instance it also loads the C instances using a join query.

Cheers,

Jan.

[Alan Knight]

Yes, it's definitely possible. Look for sends of alsoFetch: inside descriptors in the tests.

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[Jan van de Sandt]

Yes, I found an example and now it works. 

The mappings looks like this:

mapping := (aDescriptor newMapping: ToManyMapping)

attributeName: #b;

referenceClass: B;

join: (Join

from: (table fieldNamed: 'ID')

to: (bTable fieldNamed: 'A_ID')).

mapping query alsoFetch: [ :each | each c ].

Thank you!

On Thursday, June 6, 2019 at 7:02:34 PM UTC+2, alan.knight wrote:

Yes, it's definitely possible. Look for sends of alsoFetch: inside descriptors in the tests.

On Thu, 6 Jun 2019 at 09:31, Jan van de Sandt <jvds...@gmail.com> wrote:

Hello list,

With a query you can use the alsoFetch:  method to "eager load" related objects. Is it possible to specify a mapping so that Glorp does this by default?

My Model is something like this:

Class A ----(*)--> Class B ----(1)--> Class C

Class A has a collection of B instances and each B instance refers to exactly one C instance. What I would like to have is that when Glorp loads the the collection of B instances for an A instance it also loads the C instances using a join query.

Cheers,

Jan.

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[jtuchel]

Jan,

please be very sure you ALWAYS want these dependent objects loaded. We've used this just to find out there are situations in our Application where this is not desired.. ;-)

I have a related question I have been wondering about for a while:

What is the exact difference between shouldProxy: false and alsoFetch:?

All I've found out so far is that shouldProxy doesn't work as expected, but I haven't found out what exactly to expect ;-)))

Joachim

[Jan van de Sandt]

Hi Joachim,

I also tried setting shouldProxy to false. But this results in 1 + N queries instead of a single query with a join. 

You are right that specifying alsoFetch in a mapping may result in loading too much data that you don't always need. Or the related data is already cached and the fetch is also not necessary. But in my concrete situation this is not the case.

Jan.

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