Trees

[Mike Whiting]

Hi,

I'm not sure I'm understanding trees correctly.

I have ready the docs and I concluded that it might be possible to add
children to a bean by using the regular one-to-many syntax.

e.g.

$newComp = \R::dispense('component');
$newComp->name = "Foo";
$component = \R::find('component', 1);
$component->ownComponentList[] = $newComp;
\R::store($component);

However this only creates a new column on the component table
"compnent_id" with the new component id added. However, I want to
have many children!

The docs describe the canes example which uses a "ownCane" syntax but
this only has the same effect ownComponentList. i.e. a single child
created in the component table as a foreign key.

If I attempt to add multiple children like this...

$component->ownComponentList[] = $newComp;
$component->ownComponentList[] = \R::find('component', 12);

...I get an array to string conversion error.

What am I missing here?

Cheers!

[Benoit Pruneau]

The method to retrieve a bean with an ID is R::load(), not R::find().

R::load('component', 1) is equivalent to R::findOneOrDispense('component','id=1').

[Mike Whiting]

Sorry my bad. Please ignore that mistake. The rest still applies.

$component->ownComponent[] = \R::load(12);

or $component->ownComponentList[] = \R::load(12);

Both create a foreign key in the component table to a single component
rather than a join table.

Thanks

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[Mike Whiting]

I can do $component->sharedComponentList[] = \R::load(‘component’, 12); and this creates a join table but I’m not sure if this technically still a tree.


Sent from my iPhone

> On 1 Sep 2022, at 16:47, Mike Whiting <mi...@ai-em.net> wrote:
>
> Sorry my bad. Please ignore that mistake. The rest still applies.

[Benoit Pruneau]

Yes, it does create a foreign key in the component table.

In the field name 'component_id', you must understand 'Parent Id'.

Yes, a component can have many children components, but a child component must have only one parent component. The link is not set in the parent component, but in all children components.

$parentComponent = R::dispense('component');

$childComponent1 = R::dispense('component');

$childComponent2 = R::dispense('component');

$parentComponent->name='I am the parent!';

$childComponent1->name='I am the first child!';

$childComponent2->name='I am the second child!';

$parentComponent->ownComponentList[] = $childComponent1;

$parentComponent->ownComponentList[] = $childComponent2;

R::store($parentComponent);

If the table does not exist, this will create it with 3 records:

+----+--------------------------+--------------+

| id | name                     | component_id |

+----+--------------------------+--------------+

|  1 | I am the parent!         |       (null) |

|  2 | I am the first child!    |            1 |

|  3 | I am the second child!   |            1 |

+----+--------------------------+--------------+

If you now load the parent component, you can retrieve its children :

$p = R::load('component', 1);

echo $p->name;

foreach($p->ownComponentList as $c) {

    echo $c->name;

[Mike Whiting]

Thanks, but that's not really answering my question.

I think I've come to the conclusion that the Trees api is not
available when dealing with many-many relationships.

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[Mike Whiting]

I'm now stuck on Link Beans when dealing with many-many relationships
on the same table.

I am able to create the relationship by using:

$newComp = \R::load('component', 12);
$bean->link('component_component', [
'quantity' => 10,
])->component2 = $newComp;

This means that I can access the child beans in the conventional way using:

foreach($component->sharedComponentList as $c) {
echo $c->name; // prints child names
}

I can also access the links beans using:

$component = \R::load('component', 28);
foreach ($component->ownComponentComponentList as $link) {
echo $link->quantity; // prints 10
}

However when looping through the sharedComponentsList I can't
access the link bean from the other direction. i.e.

foreach($component->sharedComponentList as $c) {
echo c->ownComponentComponentList->quantity // null
}

Perhaps this is a limitation due to the table name being the same but
just wondering if there's a workaround.

Perhaps the best thing is to create a new Entity called "Dependency"
with "parent", and "child" fields where
I can also store the quantities.

Thanks

[Benoit Pruneau]

If a child component can have many parents, this is not a tree.

[Benoit Pruneau]

Ok your concern is about storing a quantity...

Effectively, the best way is to create a new Entity "Dependency". It will be clearer than "component_component"...