I wanted to query nested data until level 2 on a single model

Level 58

Certainly! The issue here is that you want to get the grandchildren (level 2 descendants) of an agent via Eloquent. This is a self-referencing relationship, but hasManyThrough expects an intermediate model that is not the same as the end model (here they're both Agent). That can cause issues, especially if you try to alias tables.

You don't need to use getThroughParent() or manually set the table alias for a simple relationship. Let's clarify how to fetch children and grandchildren (level 1 and level 2) using Eloquent relationships.

Correct Setup

Assuming your table has these fields: id, parent_id, name, etc.

1. Define children relationship

public function children()
{
    return $this->hasMany(static::class, 'parent_id');
}

2. Define grandchildren (level 2) relationship

There is no built-in hasManyThrough solution for self-referencing models that resolves table aliasing automatically. However, you can get grandchildren via children:

public function grandchildren()
{
    return $this->hasManyThrough(
        static::class, // Final model
        static::class, // Intermediate model
        'parent_id',  // Foreign key on intermediate (children) table
        'parent_id',  // Foreign key on final table (grandchildren)
        'id',         // Local key on this model (Agent)
        'id'          // Local key on intermediate (children) model
    );
}

Now, accessing level 2 agents for a specific agent:

$agent = Agent::find(1);
$level2Agents = $agent->grandchildren;

Improved Approach: Use Eager Loading

If you want to get data for level 2 in a tree structure:

$agentWithDescendants = Agent::with('children.children')->find(1);

// Access children (level 1)
$children = $agentWithDescendants->children;

// Access grandchildren (level 2)
foreach ($children as $child) {
    $grandchildren = $child->children;
    // Do something with $grandchildren
}

In Summary

If you want a flat list of level 2 agents:

public function grandchildren()
{
    return $this->hasManyThrough(
        static::class,
        static::class,
        'parent_id',
        'parent_id',
        'id',
        'id'
    );
}

If you want a nested structure, use:

public function children()
{
    return $this->hasMany(static::class, 'parent_id');
}

$agentWithDescendants = Agent::with('children.children')->find(1);

Note

You don't need getThroughParent()->setTable('agents as child_agents'). That is unnecessary and may cause errors.
Make sure your foreign keys (parent_id) and primary keys (id) are named as expected.

Ask if you need the query for deeper levels or a recursive solution!