What is the difference between BelongsTo And HasOn

问题:

Can any body tell me what is the main difference between
the BelongsTo and HasOne relationship in eloquent.

回答1:

BelongsTo is a inverse of HasOne.

We can define the inverse of a hasOne relationship using the belongsTo method. Take simple example with User and Phone models.

I'm giving hasOne relation from User to Phone.

class User extends Model
{
    /**
     * Get the phone record associated with the user.
     */
    public function phone()
    {
        return $this->hasOne('App\Phone');
    }
}

Using this relation, I'm able to get Phone model data using User model.

But It is not possible with Inverse process using HasOne. Like Access User model using Phone model.

If i want to access User model using Phone than It is necessary to add BelongsTo in Phone model.

class Phone extends Model
{
    /**
     * Get the user that owns the phone.
     */
    public function user()
    {
        return $this->belongsTo('App\User');
    }
}

You can refer this link for more detail.

回答2:

The main difference is which side of the relation holds relationship's foreign key. The model that calls $this->belongsTo() is the owned model in one-to-one and many-to-one relationships and holds the key of the owning model.

Example one-to-one relationship:

class User extends Model {
  public function car() {
    // user has at maximum one car, 
    // so $user->car will return a single model
    return $this->hasOne('Car');
  }
}

class Car extends Model {
  public function owner() {
    // cars table has owner_id field that stores id of related user model
    return $this->belongsTo('User'); 
  }
}

Example one-to-many relationship:

class User extends Model {
  public function phoneNumbers() {
    // user can have multiple phone numbers, 
    // so $user->phoneNumbers will return a collection of models
    return $this->hasMany('PhoneNumber');
  }
}

class PhoneNumber extends Model {
  public function owner() {
    // phone_numbers table has owner_id field that stores id of related user model
    return $this->belongsTo('User'); 
  }
}

回答3:

One-to-one relationship: You, as a User, can have one (hasOne) Profile. And of course the inverse also applies. Profile (belongsTo) a User. A user can't have more than one profile and a profile can't belong to multiple users.

回答4:

Here you can see a good example and see what the difference is between BelongsTo and HasOne relationship in eloquent.

Eloquent Relationships Cheat Sheet by Mahmoud Zalt https://link.medium.com/9lj9BAG8lR