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Can a relationship have more than one attribute?
In ER model, entities have attributes which can be of various types like single-valued, multi-valued, composite, simple, stored, derived and complex. But relationships can also have attributes associated to them.
What defines a many-to-many relationship?
A many-to-many relationship occurs when multiple records in a table are associated with multiple records in another table. For example, a many-to-many relationship exists between customers and products: customers can purchase various products, and products can be purchased by many customers.
Can a relationship have a key attribute?
2 Answers. The short answer is yes, it’s reasonable to have attributes associated with relationships and to have uniqueness constraints on those attributes.
How to establish a one to many relationship?
We want to establish a one-to-many relationship where many students are associated with one grade. This can be achieved by including a reference navigation property in the dependent entity as shown below. (here, the Student entity is the dependent entity and the Grade entity is the principal entity).
How to establish one to many relationship in Entity Framework?
After applying the conventions for one-to-many relationship in the entities above, the database tables for Student and Grade entities will look like below, where the Students table includes a foreign key GradeId . We want to establish a one-to-many relationship where many students are associated with one grade.
How is a relationship between two entities defined?
A relationship between two entities is defined by using two attributes which specify both ends of a relationship: In the example above we have two relationship attributes: orders and customer. When we define the entity Customer, the entity Order is not defined yet. That is why we have to put quotes around Order in the orders attribute.
What is a many to many relationship in a database?
Many-to-Many Relationship in Theory. A many-to-many (or M:N) relationship is one of the three database relationships. The other two are: One-to-one (1:1) relationships; One-to-many (1:N) relationships; By definition, a many-to-many relationship is where more than one record in a table is related to more than one record in another table.