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Today, the editor will share with you the relevant knowledge points about how to use Code First mode to manage the view in Entity Framework. The content is detailed and the logic is clear. I believe most people still know too much about this, so share this article for your reference. I hope you can get something after reading this article. Let's take a look.

I. what is a view?

View plays an important role in RDBMS (Relational Database Management system). It joins the data of multiple tables into a structure that looks like a table, but does not provide persistence. Therefore, you can think of a view as an abstraction at the top of the data of a native table. For example, we can use views to provide different levels of security, or we can simplify queries that must be written, especially since we can frequently access data defined by views in multiple places in our code. The EF Code First schema does not fully support views yet, so we must use a flexible approach. The way to do this is to really think of the view as a table, let EF define the table, delete it, and finally create a view to replace it.

Second, use EF's Code First mode to manage the view

Take books and book types as examples to explain how to use EF's Code First mode to manage views.

1. Create an entity class

The BookType entity class is defined as follows:

Using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace CodeFirstViewApp.Model {public class BookType {public BookType () {Books = new HashSet ();} public int BookTypeId {get; set;} public string BookTypeName {get; set;} public virtual ICollection Books {get; set;}

The Book entity class is defined as follows:

Using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace CodeFirstViewApp.Model {public class Book {public int Id {get; set;} public string Name {get; set;} public string Author {get; set;} public DateTime PublicationDate {get; set;} public virtual BookType BookType {get; set;}} 2, create a mock view class

Take the desired columns from multiple entities and combine them into one entity. The BookView simulation view class is defined as follows:

Using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace CodeFirstViewApp.Model {public class BookView {public int BookId {get; set;} public string BookName {get; set;} public string Author {get; set;} public DateTime PublicationDate {get; set;} public string BookTypeName {get; set;}} 3, create a configuration partner class for the simulation view class

The following code specifies the table name and primary key.

Note: the table name is also the name of the view, and the table name here must be the same as the view name in the statement that created the view.

Using CodeFirstViewApp.Model;using System;using System.Collections.Generic;using System.Data.Entity.ModelConfiguration;using System.Linq;using System.Text;using System.Threading.Tasks;namespace CodeFirstViewApp.Map {/ define configuration partner class / public class BookViewMap: EntityTypeConfiguration {public BookViewMap () {/ / set table name this.ToTable ("BookViews") / / set the primary key HasKey (p = > p.BookId);} 4. Create the seed data initializer class using CodeFirstViewApp.Model;using System;using System.Collections.Generic;using System.Data.Entity;using System.Linq;using System.Text;using System.Threading.Tasks Namespace CodeFirstViewApp.EF {public class Initializer: DropCreateDatabaseAlways {/ re-Seed method / protected override void Seed (EFDbContext context) {/ / create initialization data BookType bookType = new BookType () {BookTypeName = "Literary novel" Books = new List {new Book () {Name= "disqualification in the world", Author= "Tai Jai Zhi", PublicationDate=DateTime.Parse ("2015-08-01")}, new Book () {Name= "worry-relieving grocery store", Author= "Toano Guigo", PublicationDate=DateTime.Parse ("2014-05-01")}, new Book () {Name= "Kite Runner" Author= "Khaled Husseini", PublicationDate=DateTime.Parse ("2006-08-01")}, new Book () {Name= "A hundred years of Solitude", Author= "Garcia M á rquez", PublicationDate=DateTime.Parse ("2011-06-01")}, new Book () {Name= "Cholera Love", Author= "Garcia M á rquez" PublicationDate=DateTime.Parse ("2015-06-01")} BookType bookType2 = new BookType () {BookTypeName = "Science", Books = new List {new Book () {Name= "A brief History of humanity", Author= "Uval Herrari", PublicationDate=DateTime.Parse ("2017-01-01")} Context.BookTypes.Add (bookType); context.BookTypes.Add (bookType2); / / delete the table var drop = "Drop Table BookViews" first; context.Database.ExecuteSqlCommand (drop) / / create a view var createView = @ "CREATE VIEW [dbo]. [BookViews] AS SELECT dbo.Books.Id AS BookId, dbo.Books.Name AS BookName, dbo.Books.Author AS Author Dbo.Books.PublicationDate AS PublicationDate, dbo.BookTypes.BookTypeName AS BookTypeName FROM dbo.Books INNER JOIN dbo.BookTypes ON dbo.BookTypes.BookTypeId=dbo.Books.BookTypeId " Context.Database.ExecuteSqlCommand (createView); base.Seed (context);}

In the above code, we use the ExecuteSqlCommand () method of the Database object to destroy the generated table, and then call this method to create the view we need. This approach is useful when allowing developers to execute arbitrary SQL code on the back end.

5. Create a data context class

Add entity classes to the data context and configure relationships between entities

Using CodeFirstViewApp.Map;using CodeFirstViewApp.Model;using System;using System.Collections.Generic;using System.Data.Entity;using System.Linq;using System.Text;using System.Threading.Tasks;namespace CodeFirstViewApp.EF {public class EFDbContext:DbContext {public EFDbContext (): base ("name=AppConnection") {Database.SetInitializer (new Initializer ());} / / add public DbSet Books {get to the data context Set;} public DbSet BookTypes {get; set;} public DbSet BookViews {get; set;} protected override void OnModelCreating (DbModelBuilder modelBuilder) {/ / configure table name and primary key modelBuilder.Entity (). ToTable ("Books") .HasKey (p = > p.Id); modelBuilder.Entity () .ToTable ("BookTypes") .HasKey (p = > p.BookTypeId) / / set entity relations / / BookType and Books one-to-many foreign keys: BookTypeId modelBuilder.Entity (). HasMany (p = > p.Books) .WithRequired (t = > t.BookType) .Map (m = > {m.MapKey ("BookTypeId");}) / / add configuration partner class modelBuilder.Configurations.Add (new BookViewMap ()); base.OnModelCreating (modelBuilder);} 6, run the program

The Main () method is defined as follows:

Using CodeFirstViewApp.EF;using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace CodeFirstViewApp {class Program {static void Main (string [] args) {using (var context = new EFDbContext ()) {/ / get the data of the view var bookView = context.BookViews / / Loop through bookView.ToList (). ForEach (p = > {Console.WriteLine ("Id:" + p.BookId + ", Name:" + p.BookName + ", BookTypeName;" + p.BookTypeName + ", PublicationDate:" + p.PublicationDate);} Console.ReadKey () }}}

When you run the program, you will see that the Books and BookTypes tables and BookViews views have been generated in the database, as shown in the following figure:

The running result is as follows:

Query the view directly in the database:

Note: there is no difference between accessing a view and any data table at the code level. It is important to note that the view name defined in the Seed () method should be the same as the defined table name, otherwise an error will be reported because the table object cannot be found.

These are all the contents of the article "how to use Code First Schema Management View in Entity Framework". Thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.

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