belongsTo and hasOne have said one relationship
Foreign key table associated primary key table using the associated primary key table using the foreign key table belongsTo hasOne
For example:
First, there is the user table field id name password field
and then have user_address table id user_id city field
HasOne used in the model when the associated User user_address table, because no two tables in the user table associated with the foreign key
Use belongsTo, in UserAddress model when the associated user table as a foreign key user_id has two tables in the associated table user_address