I am having doubt regarding using multiple values for same project
Basically I have 3 models
1-Company Table,
2-Project Table,
3-Contact_person Table
So, in project table I want to assign multiple values of contact person
That is I can have multiple contact_person for a single project
From a specific company
Project table fields are
"Company table Fields"
Company_Id,
Company_name,
"Contact person Table fields"
Company name(Foreign key),
Contact person name,
"Project Table"
Company name(Foreign key) ,
Project name,
Contact person(foreign key)
So here in project table in contact person field I want to have multiple contact person, from that same company
So can anyone write me out model for contact person table
you are trying to make a relationship one to many for company to project and one to many for both company and project to contactperson.
Try to make a many to many relationship between contactperson and project. Once it is done your model will work fine.
https://docs.djangoproject.com/en/3.1/topics/db/examples/many_to_many/
In this way you can add multiple Contact persons for a Project.
I recommend many to many relationships, register model, create a view, and use it in HTML. It should work fine.
Related
I Need to Design a database for a system where there's Customers and Vendors but they both are related to entity called Users where every user is either a customer or a vendor .
the problem is that Vendors are related to other entities that Customers aren't .
so how can I design such a database ?
The other entities will store the ID of the Vendor as a foreign key. And Vendors and Customers are not going to be in the same table anyway*, so it's not like the two have IDs that might be used at the same time for that.
Also, to add, the Foreign Key you require for User could be managed as an add/edit trigger if your DB of choice allows it. That way you can make sure that the Vendor id used for those related entities isn't a User ID linked to Customers. (...WHERE userid NOT IN (SELECT userid FROM users WHERE customer = TRUE))
* Customers and Vendors have different properties/fields so shouldn't be in the same table.
You could have Vendors and Customers have a relationship to a User table.
user
===========
userId
name
vendor
===========
vendorId
companyName
userId
customer
===========
customerId
source
userId
Then you can link to both customers and vendors from the same table, yet they can still share the same common data in the user table. In fact, a customer could also be a vendor.
Your question could be generalized as follows: how do I express subclasses in relational tables?
For the generic answer, see this:
https://stackoverflow.com/tags/class-table-inheritance/info
I have read this (Database design: 3 types of users, separate or one table?)
I decided to put admin and normal user in one table since the attributes are similar:
fullname,
address,
phone,
email,
gender
...
Then I want to draw ERD, suddenly my mind pop out a question.
How to draw?
Customer make appointment and admin approve appointment.
now only two tables.
Help.
Employee Table - Customers Table - appointment Table
Self join relationship Employee Has manager Id
I want to create an entity relationship diagram for a three way relationship in the following contrived situation:
Each COMPANY has many DEPARTMENTS. An EMPLOYEE can work simultaneously for many DEPARTMENTs. However, an EMPLOYEE can work for only one DEPARTMENT of a COMPANY. In other words, the EMPLOYEE works for as many DEPARTMENTS as COMPANYs.
What kind of associations and relationships will such a diagram have? My purpose is not to create tables in a database but just as an aid to understanding.
Thanks in advance for your help!
COMPANY_EMPLOYEE_DEPARTMENT:
COMPANY (PK)
EMPLOYEE (PK)
DEPARTMENT
Each combination of company and employee, can only be associated with one department. That is, an employee can only work for one department in each company.
This should work as long as a department does not belong to more than one company, and that the COMPANY_EMPLOYEE_DEPARTMENT relation does not link a department of one company with another company.
I have a database with a "users" table containing data about my users. Each user is to be linked to a company or a college. I wish to have two separate tables "college" and "company" each with a field "ID". So how do I link each record in the users table to either a company or a college?
The basic thing is that I wish to establish an "OR" relationship in the database.
You can use subtype/super-type relationship. Keep all common fields in the organization table. College and company tables contain only fields specific to those entities.
You could use an 'institution' or 'organisation' lookup table, with a structure something like
InstitutionId[PK], InstitutionType, LookupKey
where LookupKey is the PK to either Company or College.
Or,
InstitutionId[PK], CompanyId[FK], CollegeId[FK]
In both cases you link from user to institution, then onto Company and/or College.
I personally prefer the second option, because it allows you to easily validate the FK relationship and also allows (if applicable) for a user to be a member of a company and/or a college.
I would create relationtables. UserCollege and UserCompany. This way you are even able to have users that are linked to both if needed in the future. If not you simply just create a relationrecord on one of the both
I have a problem with a many-to-many relation in my tables, which is between an employee and instructor who work in a training centre. I cannot find the link between them, and I don't know how to get it. The employee fields are:
employee no.
employee name
company name
department job title
business area
mobile number
ext
ranking
The Instructors fields are
instructor name
institute
mobile number
email address
fees
in a many-to-many relationship the relationships will be in a 3rd table, something like
table EmployeeInstructor
EmployeeID
InstructorID
to find all the employees for a specific instructor, you'd use a join against all three tables.
Or more likely there will be classes involved --
Employee takes Class
Instructor teaches Class
so you'll have and EmployeeClass table,
an InstructorClass table,
and join through them. And Class needs to be unique, or else you'll need
Class is taught in Quarter on ClassSchedule
and end up joining EmplyeeClassSchedule to InstructorClassSchedule.
This ends up being one of your more interesting relational designs pretty quickly. If you google for "Terry Halpin" and "Object Role Modeling", this is used as an illustrative situation in the tutorial.
First of all, you will need a unique key in both tables. The employee number may work for the employee table, but you will need another for the instructor table. Personally, I tend to use auto incrementing identity fields called ID in my tables. This is the primary key.
Second, create a new table, InstructorEmployee. This table has two columns, InstructorID and EmployeeID. Both fields should be indexed. Now you can create an association between any Employee and any Instructor by creating a record which contains the two IDs.