In the world of software development, particularly when working with databases, understanding how to effectively manage data is crucial. This is where Entity Framework (EF) comes into play—a powerful Object-Relational Mapping (ORM) framework for .NET applications that simplifies database interactions. At the heart of EF lies a concept known as an 'entity.' But what exactly does this mean?
An entity in Entity Framework represents a class that maps directly to a table within your database. Imagine each entity as a blueprint; it defines the structure and properties of data you want to store. For instance, consider a school application where we have two domain classes: Student and Grade. These classes become entities once they are included as DbSet<TEntity> properties within your context class.
Here's how it looks:
public class Student {
public int StudentID { get; set; }
public string StudentName { get; set; }
public DateTime? DateOfBirth { get; set; }
public byte[] Photo { get; set; }
public decimal Height { get; set; }
public float Weight { get; set;
}
publlic class Grade {
public int GradeId {get ;set;}
bublic string GradeName{get ;set;}
bublic string Section{get ;set;} ICollection<Student> Students{get ;set;} } ```
When these classes are part of your context—let's say it's called `SchoolContext`—they represent tables named `Students` and `Grades` in your database.
Entities can include different types of properties:
1. **Scalar Properties**: These are primitive type properties like integers or strings that map directly to columns in the corresponding database table. In our example, attributes such as `StudentID`, `StudentName`, and others fall under this category.
2. **Navigation Properties**: These define relationships between entities, allowing you to navigate from one entity to another easily.
- **Reference Navigation Property**: If an entity has a property representing another single entity type (like linking students to their grades), it’s termed reference navigation property.
- **Collection Navigation Property**: Conversely, if an entity includes multiple instances of another type (for example, all students belonging to one grade), that's referred to as collection navigation property.
3. The EF API automatically creates foreign key columns based on these relationships when setting up the underlying database schema.
4. An interesting aspect about entities is their state management during their lifecycle within EF’s context—which tracks changes made through operations like adding or modifying records via methods like `.SaveChanges()`. Each operation affects its state represented by enums such as Added, Modified, Deleted etc., ensuring efficient change tracking throughout development cycles.