How can I establish a Laravel relationship using a non-standard primary key column?

Below is one way to solve the issue. In your models you must both:

1. Tell Laravel that the primary key for the woocommerce_sessions table is not “id” but “session_id” (by setting the model’s $primaryKey property).
2. Define the proper relationship type in each model so that you aren’t applying an extra lookup (for example, avoid chaining find() on top of an already constrained relation).

Let’s break it down.

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Step 1. Set the Primary Key on the Session Model

In your WoocommerceSessions model, add this property:

PHPCopied
class WoocommerceSessions extends Model
{
    protected $primaryKey = 'session_id';

    // If your primary key is non-incrementing (which is likely), also set:
    public $incrementing = false;

    // Optionally, set the key type if it isn’t an integer
    protected $keyType = 'string'; // if applicable

    public function product(): BelongsTo
    {
        // Use `session_id` from sessions to match the posts table primary key “ID”
        return $this->belongsTo(Post::class, 'session_id', 'ID');
    }
}

This ensures that Laravel is aware that the primary key for woocommerce_sessions is “session_id.”

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Step 2. Correct the Relationship in the Posts Model

Because the posts table is the parent record (the one that is referenced by the session), a post would typically have one (or many) related session entries. Therefore, in the Posts model you’d usually define a hasOne (or hasMany) relationship rather than a belongsTo. For example, if each product (post) has only one session record:

PHPCopied
class Post extends Model
{
    // The primary key “ID” is already the default if you use it as is.

    public function session(): HasOne
    {
        // Note: The foreign key is in the woocommerce_sessions table.
        return $this->hasOne(WoocommerceSessions::class, 'session_id', 'ID');
    }
}

If there can be multiple session records for a given post then use hasMany instead.

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Step 3. Retrieve the Related Product Without Extra Filtering

In your current code you wrote:

PHPCopied
$product = $this->product()->find($c['product_id']); // returns null

Since your relationship already matches the session’s “session_id” with the product’s “ID”, calling find() (which adds an extra “where” clause on the primary key) can conflict with what the relationship already defines. Instead, simply load the related product directly:

PHPCopied
$product = $this->product; // if using the property accessor

or if you need to work with the query builder before executing, simply use:

PHPCopied
$productQuery = $this->product();
$product = $productQuery->first();

In short, do not mix the relationship constraints with an additional lookup by primary key unless you intend to override them.

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Summary

• Set the correct primary key: In WoocommerceSessions, add
  protected $primaryKey = 'session_id';

• Use the appropriate relationship type:
  In WoocommerceSessions, use belongsTo (because session holds the foreign key) and in Posts use hasOne or hasMany (because posts are the “parent”).

• Avoid extra lookups: Remove or adjust the find() call on the relationship so the built-in constraint isn’t overridden.

Implementing these changes will allow Laravel to properly match the session’s “session_id” with the post’s “ID” and return the correct related product.