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Entity framework core

· 3 min read

Introduction​

  • Entity Framework Core is an ORM framework, open-source, lightweight and cross-platform developed by Microsoft.
  • It enables developers to work with databases using .NET object and EF Core is built on top of ADO.NET

Relationship​

One-to-One Relationship​

modelBuilder.Entity<Author>()
    .HasOne(a => a.Book)           // Author has one Book
    .WithOne(b => b.Author)        // Book has one Author
    .HasForeignKey<Book>(b => b.AuthorId);  // Foreign key in Book referencing AuthorId

One-to-Many Relationship​

modelBuilder.Entity<Author>()
    .HasMany(a => a.Books)         // Author has many Books
    .WithOne(b => b.Author)        // Book has one Author
    .HasForeignKey(b => b.AuthorId);       // Foreign key in Book referencing AuthorId

Many-to-Many Relationship​

modelBuilder.Entity<StudentCourse>()
    .HasKey(sc => new { sc.StudentId, sc.CourseId });   // Define composite primary key for the join table

modelBuilder.Entity<StudentCourse>()
    .HasOne(sc => sc.Student)
    .WithMany(s => s.Courses)
    .HasForeignKey(sc => sc.StudentId);  // Foreign key in join table referencing StudentId

modelBuilder.Entity<StudentCourse>()
    .HasOne(sc => sc.Course)
    .WithMany(c => c.Students)
    .HasForeignKey(sc => sc.CourseId);  // Foreign key in join table referencing CourseId

DeleteBehavior​

The DeleteBehavior enum in EF Core includes the following options:

  1. Cascade: Deleting the principal/parent entity will cause the dependent/child entities to be deleted as well. OnDelete(DeleteBehavior.Cascade)

  2. SetNull: Deleting the principal/parent entity will set the foreign key properties in the dependent/child entities to null. OnDelete(DeleteBehavior.SetNull)

  3. SetDefault: Deleting the principal/parent entity will set the foreign key properties in the dependent/child entities to their default values. OnDelete(DeleteBehavior.SetDefault)

  4. Restrict: Prevents the deletion of the principal/parent entity if there are dependent/child entities. OnDelete(DeleteBehavior.Restrict) . An exception will be thrown.

  5. NoAction: Similar to Restrict, it is used to specify no action on delete. OnDelete(DeleteBehavior.NoAction) and you'll need to handle constraints in your application logic.

For example:

modelBuilder.Entity<ParentEntity>()
    .HasMany(p => p.ChildEntities)
    .WithOne(c => c.ParentEntity)
    .OnDelete(DeleteBehavior.Restrict);

This configuration would set the delete behavior for the relationship between ParentEntity and ChildEntity to Restrict.

Best pratices​

  1. Indexing: Creating indexes on frequently accessed columns can improve query performance.

  2. Proper data modeling: Designing tables and relationships properly can improve query performance and prevent performance issues.

  3. Caching: Storing frequently accessed data in a cache can reduce database calls and improve application performance.

  4. Query optimization: Writing efficient queries can improve performance. Techniques such as avoiding unnecessary joins and reducing the number of returned columns can help.

  5. Connection pooling: Reusing database connections instead of creating new ones can improve performance.

  6. Batch processing: Performing multiple operations in a single database call can improve performance and reduce overhead.

  7. Asynchronous programming: Using asynchronous programming techniques can improve performance by allowing the application to continue executing while waiting for database calls to complete.