Entity Framework - Entity Relationships


In relational databases, relationships (associations) between the tables are defined through foreign keys. A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables. There are three types of relationships: 1. one-to-one, 2. one-to-many, and 3. many-to-many.

 

One-to-One Relationship

In one-to-one relationship, the primary key acts additionally as a foreign key and there is no separate foreign key column for either table.


One-to-Many Relationship

In one-to-many relationship, the foreign key is defined on the table that represents the many end of the relationship.


Many-to-Many Relationship

The many-to-many relationship involves defining a third table (called join table), whose primary key is composed of the foreign keys from both related tables. Many-to-Many relationship is being managed by C-S mapping in EDM.

Note:
Entity framework supports many-to-many relationship only when the joining table does not include any columns other than PKs of both the tables. If the join tables contain additional columns, such as DateCreated, then the EDM creates entity for middle table as well and you will have to manage CRUD operation for many-to-many entities manually.


Entity Graph

When an entity has relationship with other entities, then the full object hierarchy is called entity graph.

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