Is there any explanation with example of many2many fields? What is the difference between relational tables and models ??
suppose you have two table teacher and student...
student has multiple teacher and teacher also has multiple students so here we can not apply many2one and many2one relationship so we need to add many2many relationship on this two tables...
suppose in odoo we have two model 'student.student' and 'teacher.teacher' so we can apply many2many relationship like this in student.student model
techer_ids = fields.Many2many('teacher.teacher', 'student_teacher_rel', string='Teachers')
how it works,
it will create different table in database with name student_teacher_rel .
this table has two column teacher_id and student_id both are foreign key of student table and teacher table...
so we can easily manage relationship between them...
Related
I'm a newbie in database design.
Can anybody look at this design:
Initially I created these tables - m2m relation first. It was simple:
students
contacts
contact_types
But new table teachers was added into database after that.
...and each teacher may have contact too.
I just added new column into contacts "junction" table.
But I don't like this design, because there are empty values in columns of teacher_id and student_id columns.
Is there better way to create many-to-many relations for that situation?
Main goal is to get ability of adding multiple contacts for one student/teacher.
The former variant of my design, but I don't know if it is optimal or not.
To allow your design to be M:M you need something like this:
table teacher { id, .... }
table student { id, ...}
table contact { id, typeId, value }
table contactType {id, ....}
table contact_teacher {contactId, teacherId}
table contact_student {contactId, studentId}
Then you have your M:M relationship between student and contact and teacher and contact
The right way to create a many to many relationship between teachers and contacts is to create a "joining table" that table would look like this:
contactteacher table
name type
id int - auto increment
teacherid int
contactid int
I like to call the tables by the things they join ordered alphabetically that is why I suggest the name contactteacher
There might be additional information for contact -- like where you met someone or when you met them.
There could also be meta data in the table -- when the record was created when it was edited, who created it -- etc.
I have two tables
student(sid,sname,sage,sgender,semail)
Course(cid,cname,credit)
where one student can enroll for only 1 course and in one course there can be many students.
so should I use the foreign key in the course table or creating a new table for enrollment.
Is this approach depends on the situation or others?
Based on your current scenario, you should create foreign key in your students table similar like s_cid.
But rather I suggest create separate table for enrollment, thinking of possible future requirement change where student can attend multiple courses. So you would have enrollment table with id, sid, cid columns.
I have a one-to-many relationship for Gym to User relationship. That being a Gym can have multiple users, but a User can only have one gym.
Is it better to have a pivot table for this to link gym_id to user_id like follows?
Gym_User Table:
gym_id | user_id
or in the User table like follows?
User Table:
id | name | password | gym_id
Pivot tables are used when having many-to-many relationship.But for your case, you have One-to-many relationship. And don't need a pivot table.
A typical example of many-to-many relationship is Article & Tags. Where 1 article can have many tags and 1 tag can belong to many articles.
But yours is simple one-to-many relationship.
You have a 1 to many relationships, in this case you donot need pivot table, gym_id is foreign key in the user table and you will define relations on the models.
In gym model you will define a hasMany relationship to user model and in user model define belongsto relationship to gym model. (Refer to Laravel documentation).
One of nice example for pivot table is Access Controller Models
Such as User,Role and Permission..
Hi I am trying to make a database for academy that offers courses ,
I have two tables that have many-many relation ship,
which are:
Student id(PK)
name
number
NationalID
absences
and the Second table is courses
cid(PK)
cname
cpercentage
chours
type
so now according to the design rules i must create a third table for the relationship that has the both keys for student and course
Enrolls
id
cid
now in mysql i inserted both of these columns as a child and got the reference from the 2 main tables ,
now my question is : is this table(Enrolls) will got modified by default whenever i add a course or student , or should i modify it by myself ?
thanks every body.
This is a many-to-many relationship, you have two main tables and a middle table which will make the relationship betwin those 2 main tables. One student can attend more than one course and one course can be attended by many students. The answer for your question si yes you have to insert also into the midle table which is Enrols.
I am using DBDesigner 4 for designing my database relations.
I have a users table and a recipes table. One user can own many recipes but one recipe cannot be owned by many users. This relationship is shown by the user_recipes relation in the picture. (A one-to-many relationship from users to recipes).
However, recipes can be liked by users. Many users can like many recipes. This is a many-to-many relationship between users and recipes and the pivot table for this is users_like_recipes.
But when I create this pivot table, I only need the users_id and recipes_id column. The recipes_users_id column is getting added on its own and I am not able to remove it. It says the third column has come from another Relation which is defined in the model. I guess its the user_recipes relation.
When I remove the user_recipes relation, I get the pivot table like I want to.
But I need the user_recipes relation too!
Please. Any help would be appreciated.
I would suggest removing user_id as a primary key from from the recipes table. Currently the combination if id and user_id provides identification for your recipes table. In this situation multiple user_id's can create the same recipe id because the combination has to be unique. user_id can just be a normal column in your table. If you REALLY want to, you can make an alternate key on (id, user_id) but you do not need it because the id is unique.