Suppose I have 2 entity set one user and other books and the user contains two types of user.roles : student and admin the admin adds books and student reads them so how to I represent these entity user and books with relations reads and adds in an ER Diagram.

CodePudding user response：

Presumably both of those are many to many relationships, so the most common thing to do would be to explicitly include the join tables, each of which would be a many to many between books and users, but would be named appropriate to distinguish thier functions.

CodePudding user response：

The top line is representing the admin role. I assumed a book is added by only by one admin and an admin may add many books. A book is required to be added by an admin and an new admin may not have added any books.

The bottom line is representing the student role. A student may read many books and a book may be read by many students. A student may not have read any books and a book my not yet have been read by a student.

The answer already included here mentioned you need a join table for the many-to-many relationship when putting this into a DBMS. The notation here is crow's foot. Here is a link for an explanation of the notation if you're not familiar, https://vertabelo.com/blog/crow-s-foot-notation/.