Consider the node chart below:

As shown in the image above, I want to create a function that can tell me the depth of a relationship from the top-level node.

Instance Model

/**
 * Get the immediate parent instance of the instance.
 */
public function parent()
{
    return $this->hasOne(Instance::class);
}

/**
 * Get the children instances of the instance.
 */
public function children()
{
    return $this->hasMany(Instance::class);
}

/**
 * Get the depth of an instance.
 * @return int
 */
public function getDepthAttribute()
{
    // TODO
}

Instance Table

Schema::create('instances', function (Blueprint $table) {
    $table->id();
    $table->string('name', 32);
    $table->foreignId('instance_id')->nullable();
    $table->timestamps();
});

Schema::table('instances', function (Blueprint $table)
{
    $table->foreign('instance_id')->references('id')->on('instances')->onUpdate('cascade')->onDelete('cascade');
});

Instance table example

id    name     instance_id | (getDepthAttribute() should return)
-------------------------- |
1     A        NULL        |  0
2     B        1           |  1
3     C        2           |  2
4     D        3           |  3
5     E        3           |  3
6     F        3           |  3

In a phrase, my problem is: "If an instance has a parent instance, add 1. Repeat until the parent instance does not have a parent instance. Then return the final value."

How can I accomplish this properly in Laravel?

CodePudding user response：

My solution isn't using recursion, and I don't know how it will perform with a large data. I don't think it will be an issue, but I suggest you seed a huge table and measure the performance. My solution is to create an array of depth map.

public $depthMap = [];
public $data = [
    ['id' => 1, 'name' => 'a', 'iid' => null],
    ['id' => 2, 'name' => 'b', 'iid' => 1],
    ['id' => 3, 'name' => 'c', 'iid' => 2],
    ['id' => 4, 'name' => 'd', 'iid' => 2],
    ['id' => 5, 'name' => 'e', 'iid' => 3],
    ['id' => 6, 'name' => 'f', 'iid' => 4],
    ['id' => 7, 'name' => 'g', 'iid' => 3],
    ['id' => 8, 'name' => 'h', 'iid' => 5],
    ['id' => 9, 'name' => 'i', 'iid' => null],
    ['id' => 10, 'name' => 'j', 'iid' => 7],
    ['id' => 11, 'name' => 'k', 'iid' => 9],
    ['id' => 12, 'name' => 'l', 'iid' => 10],
    ['id' => 13, 'name' => 'm', 'iid' => 4],
    ['id' => 14, 'name' => 'n', 'iid' => 3],
    ['id' => 15, 'name' => 'o', 'iid' => 12],
    ['id' => 16, 'name' => 'p', 'iid' => 10],
];

public function handle()
{
    foreach ($this->data as $item) {
        $this->depthMap[] = trim($this->getDepth($item) . ".{$item['id']}", '.');
    }
}

public function getDepth($item)
{
    foreach (array_reverse($this->depthMap) as $mapItem) {
        if (array_reverse(explode('.', $mapItem))[0] == $item['iid']) return $mapItem;
    }
    
    return '';
}

/* The output
[
    "1",
    "1.2",
    "1.2.3",
    "1.2.4",
    "1.2.3.5",
    "1.2.4.6",
    "1.2.3.7",
    "1.2.3.5.8",
    "9",
    "1.2.3.7.10",
    "9.11",
    "1.2.3.7.10.12",
    "1.2.4.13",
    "1.2.3.14",
    "1.2.3.7.10.12.15",
    "1.2.3.7.10.16",
]; 
*/

Now, you can make explode(), array_reverse(), count() operations to now not only the length of the depth but also the whole releation map.

CodePudding user response：

Below is the solution I came up with:

DepthHelper.php

use \App\Models\Instance;
/**
 * Returns the depth of an Instance
 * @param $idToFind
 * @return int
 */
function DepthHelper($idToFind){
    return GetParentHelper($idToFind);
}

// Recursive Helper function
function GetParentHelper($id, $depth = 0) {
    $model = Instance::find($id);

    if ($model->instance_id != null) {
        $depth  ;

        return GetParentHelper($model->instance_id, $depth);
    } else {
        return $depth;
    }
}

Instance Model

    /**
     * Get the depth of this instance from the top-level instance.
     */
    public function getDepthAttribute()
    {
        return DepthHelper($this->id);
    }

    protected array $appends = ['depth'];