MVC & WebAPI

Models: Data model Views: UI Components Controllers: Handle browser requests, retrieve model data then return a response Service Layer: Additional layer that separates validation logic from your controller

Ideas behind MVC:

• Separation of converns. E.G. Views don't handle business logic

Controller

• MVC implements URL routing logic in this format: /[Controller]/[ActionName]/[Parameters]
• public string Index() : BaseURL method
• MapControllerRoute : URL template where you define parameters of a route
• Components of a route method
  • IActionResult : Interface for contracts that return the result of an action method. Generally return this or a something derived from ActionResult
  • View method : Renders the view
    • If the view is not specified, MVC defaults to using the view with the same name as the action method
    • E.G. /HelloWorld/Index --> /Views/HelloWorld/Index.cshtml
• How to pass data from controllers to views?
  • The preferred method is to use a View Model
  • View Model : Pass strongly typed models using the queryset as a parameter in the View() method. You can define the model to be passed to a view with a @model directive
  • Controllers can set ViewData K/V pairs which can be used in the Views through the ViewData dictionary. These models are not strongly typed.

Views

• Views/_ViewStart.cshtml brings in shared layouts to each view
• Layout : Reduce duplicated code in views by specifying common structure in a webpage
  • The default page is named _Layout.cshtml by convention
  • 
• Views should avoid doing business logic or interacting with the db directly

View Model: Alternate way to prevent overposting

• Not the same as Data Transfer objects (DTO). View models encapsulate behaviour while DTOs cannot
• View models cannot be serialised unlike DTOs, so they are not used in SPAs

Models

• DbContext : Represents the unit of work
  • KNOWS Entities that have been previously queried on it --> This can introduce bugs
• DbSet

Register DbContext with the dependency injection container

Foreign Keys:

• A One-To-One relationship requires:
  • A primary key on the principal entity
    • Optional: Reference navigation to principal
    • By default, Id is the primary key
  • A foreign key on the dependent entity
    • Optional: Reference navigation to principal
    • By default, EF makes a property as a foreign key when its name matches with the principal entity's primary key
• Use [ForeignKey(name) to override the default attribute for a foreign key
  • https://www.entityframeworktutorial.net/code-first/foreignkey-dataannotations-attribute-in-code-first.aspx

using System.ComponentModel.DataAnnotations.Schema;
public class Post  {  // principal
  public int Id { get; set; }
  public ICollection<Comment> Comments { get; set; }  // One to many relationship with Comment
}

public class Comment  { // dependent
  public int Id { get; set; }
  public int PostId { get; set; } // Reference to Post's PK makes this the foreign key
  public Post Post { get; set; }  // Reference navigation to principal
}

Conditions & DataAnnotation Attributes on Entity attributes:

• required keyword : Used to prevent warning on uninitialized non-nullable values.
• Many-to-one relationships: Uze ICollection<>
• Can override OnModelCreating in your DbContext and do custom configuration with the fluent API
• [Comment("")]
• [MaxLength(X)]
• [Unicode] configured as unicode by default
• [Column(Order = X)]

Default Values

• [DatabaseGenerated(DatabaseGeneratedOption.Identity)] value generated on inserted entities (On ANY INSERT)
• [DatabaseGenerated(DatabaseGeneratedOption.Computed)] value generated on add or update
• ^ is equvalent to:

modelBuilder.Entity<Blog>()
    .Property(b => b.Rating)
    .HasDefaultValue(3);

• EF Core doesn't specify a default way to set timestamps:

modelBuilder.Entity<Blog>()
    .Property(b => b.Created)
    .HasDefaultValueSql("getdate()");

• Computed values:

modelBuilder.Entity<Person>()
    .Property(p => p.DisplayName)
    .HasComputedColumnSql("[LastName] + ', ' + [FirstName]");

JSON Columns: Requires EF Core 7

• Release Notes

Select:

• _context.model.FirstOrDefaultAsync: Select one or return default
  • SingleOrDefaultAsync: throw error if more than one (extra work unnecessary if you just select one)
  • FindAsync: Find entity with PK

Model validation:

• TODO: https://learn.microsoft.com/en-us/aspnet/core/mvc/models/validation?view=aspnetcore-7.0
• Encountering this error frequently?

Loading related data:

• Lazy loading by default --> Data is not retried until a navigation property is accessed
• Eager loading: Use Include and ThenInclude to read related classes in a larger, single query
• Explicit loading: Use Load method to do explicit loading

Performance:

• Pagination
• Limiting number of fetched objects with Take

Service Layer

WebAPI

• Data Transfer Object (DTO)