Many2many fields use the same table and columns while inheriting with _name field Odoo13

Question

This error is thrown up when "hr.employee" or any other model with Many2many field is inherited to my model in odoo13.

Traceback (most recent call last):


File "/opt/odoo/odoo/modules/registry.py", line 59, in __new__
        return cls.registries[db_name]
      File "/opt/odoo/odoo/tools/func.py", line 69, in wrapper
        return func(self, *args, **kwargs)
      File "/opt/odoo/odoo/tools/lru.py", line 44, in __getitem__
        a = self.d[obj].me
    KeyError: 'shorepoint'

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "/opt/odoo/odoo/modules/registry.py", line 85, in new
        odoo.modules.load_modules(registry._db, force_demo, status, update_module)
      File "/opt/odoo/odoo/modules/loading.py", line 423, in load_modules
        registry.setup_models(cr)
      File "/opt/odoo/odoo/modules/registry.py", line 247, in setup_models
        model._setup_fields()
      File "/opt/odoo/odoo/models.py", line 2684, in _setup_fields
        field.setup_full(self)
      File "/opt/odoo/odoo/fields.py", line 418, in setup_full
        self._setup_regular_full(model)
      File "/opt/odoo/odoo/fields.py", line 3151, in _setup_regular_full
        raise TypeError(msg % (self, field))
    TypeError: Many2many fields school.student.category_ids and hr.employee.category_ids use the same table and columns

Here is my code:

from odoo import models, fields, api

class school_management(models.Model):
    _name = 'school.student'
    _inherit = 'hr.employee'
    _description = 'Model to manage school students'

Answer 1

In hr application the field category_ids was defined like this:

    category_ids = fields.Many2many(
          'hr.employee.category', 'employee_category_rel',
          'emp_id', 'category_id',
          string='Tags')

they specified the name of relation and columns so when he inherited the hr.employee in your custom model the same definition of category_ids is used for your model, this why Odoo is confused you used the same relation and columns to define a many2many relation for two different model. all you have to do is remove this ambiguity by specifying a new relation name for you many2many field.

class school_management(models.Model):
    _name = 'school.student'
    _inherit = 'hr.employee'
    _description = 'student' # this will be used to log message when you create a student, so keep it simple, when you create a record message will be 'student is created' 

    # define new relation name and better column names 
    # and I think you need a new category model because this one is used for employee category, may be it's better to create hr.student.category table I don't know it's up to you
    category_ids = fields.Many2many(
      'hr.employee.category', 'student_category_rel',
      'student_id', 'category_id',
      string='Tags')

I hope this helps you.