ORM Technologies and Entity Framework (EF)

ORM Technologies and Entity Framework (EF)

ORM Technologies and Entity Framework (EF) Entity Framework, DbContext, CRUD Operations, Code First, Migrations Svetlin Nakov Inspiration Manager Software University http://softuni.bg Table of Contents 1. ORM Technologies Basic Concepts 2. Entity Framework Overview 3. Database First with EF

4. Reading Data and CRUD operations with EF 5. Code First with EF Domain Classes and DbContext 6. Migrations in EF 2 Introduction to ORM Technologies What is Object-Relational Mapping (ORM)? ORM Technologies Object-Relational Mapping (ORM) is a programming technique

for automatic mapping data and database schema Map relational DB tables to classes and objects ORM creates a "virtual object database" Used from the programming language (C#, Java, PHP, ) ORM frameworks automate the ORM process A.k.a. Object-Relational Persistence Frameworks 4 ORM Mapping Example Relational database

schema ORM Framework ORM Entities (C# classes) 5 Entity Framework (EF) Object-Relation Persistence Framework for .NET

Overview of EF Entity Framework (EF) is the standard ORM framework for .NET Maps relational database to C# object model Powerful data manipulation API over the mapped schema CRUD operations and complex querying with LINQ Database first approach: from database to C# classes Code first approach: from classes to DB schema Visual Studio generates EF data models Data mappings consist of C# classes, attributes and XML 7 EF: Basic Workflow 1. Define the data

model (use a DB visual designer or code first) 2. Write & execute query over IQueryable 3. EF generates & executes an SQL query in the DB 8

EF: Basic Workflow (2) 4. EF transforms the query results into .NET objects 5. Modify data with C# code and call "Save Changes" 6. Entity Framework generates & executes SQL

command to modify the DB 9 Database First with Entity Framework and Visual Studio Live Demo Entity Framework Components The DbContext class DbContext holds the DB connection Holds and DbSet for the entity classes Provides LINQ-based data access ( through IQueryable)

Provides API for CRUD operations Entity classes Hold entities (objects with their attributes and relations) Each database table is typically mapped to a single C# entity class 11 Reading Data with LINQ Query We can also use extension methods for constructing the query using (var context = new SoftUniEntities()) { var employees = context.Employees This is called projection .Select(c => c.FirstName)

.Where(c => c.JobTitle == "Design Engineering") .ToList(); This is called ToList() method } Find element by id executes the SQL query selection using (var context = new SoftUniEntities())

{ var project = context.Projects.Find(2); Console.WriteLine(project.Name); } 12 Creating New Data To create a new database row use the method Add() of the corresponding collection: var project = new Project() Create a new { project object Name = "Judge System",

StartDate = new DateTime(2015, 4, 15) }; Mark the object for inserting context.Projects.Add(order); context.SaveChanges(); This will execute an SQL INSERT SaveChanges() method executes the SQL insert / update / delete commands in the database 13

Cascading Inserts We can also add cascading entities to the database: Employee employee = new Employee(); employee.FirstName = "Petya"; employee.LastName = "Grozdarska"; employee.Projects.Add(new Project { Name = "SoftUni Conf" } ); softUniEntities.Employees.Add(employee); softUniEntities.SaveChanges(); This way we don't have to add Project individually They will be added when the Employee entity (employee) is

inserted to the database 14 Updating Existing Data DbContext allows modifying entity properties and persisting them in the database Just load an entity, modify it and call SaveChanges() The DbContext automatically tracks all changes made on its entity objects Employees employee = softUniEntities.Employees.First(); employees.FirstName = "Alex"; context.SaveChanges(); This will execute

This will execute an SQL SELECT to load the first order an SQL UPDATE 15 Deleting Existing Data Delete is done by Remove() on the specified entity collection SaveChanges() method performs the delete action in the database Mark the entity for Employees employee =

softUniEntities.Employees.First(); deleting at the next save softUniEntities.Employees.Remove(employee); softUniEntities.SaveChanges(); This will execute the SQL DELETE command 16 Native SQL Queries var context = new SoftUniEntities(); Parameter string nativeSQLQuery = placeholder "SELECT FirstName + ' ' + LastName " +

"FROM dbo.Employees WHERE JobTitle = {0}"; var employees = context.Database.SqlQuery( nativeSQLQuery, "Marketing Specialist"); foreach (var emp in employees) { Console.WriteLine(emp); } Parameter value Return type

17 CRUD Operations with EF Live Demo "Code First" Approach in EF From Classes to DB Schema Database First in EF Create database schema and generate C# code (models) from it DB EDMX Model

Domain Classes 20 Code First in EF DbContext & ModelBuilder Domain classes Custom

Configuration DB As needed 21 Domain Classes (Models) Bunch of normal C# classes (POCO) May hold navigation properties public class PostAnswer Primary key

{ public int Id { get; set; } public string Content { get; set; } Foreign key public int PostId { get; set; } public virtual Post Post { get; set; } } Navigation property Virtual for lazy loading 22 Domain Classes (Models) (2) Another example of domain class (model)

public class Post { This prevents public Post() NullReferenceException { this.Answers = new HashSet(); Navigation } property public virtual ICollection Answers { get; set; } Enumeration public PostType Type { get; set; } }

23 Defining the DbContext Class using System.Data.Entity; using CodeFirst.Models; Put all entity classes as DbSets public class ForumContext : DbContext { public DbSet Categories { get; set; } public DbSet Posts { get; set; } public DbSet PostAnswers { get;

set; } public DbSet Tags { get; set; } } 24 CRUD Operations with EF Code First var db = new ForumContext(); var category = new Category { Name = "Database course" }; db.Categories.Add(category); var post = new Post(); post.Title = "Homework Deadline"; post.Content = "Please extend the homework deadline"; post.Type = PostType.Normal;

post.Category = category; post.Tags.Add(new Tag { Text = "homework" }); post.Tags.Add(new Tag { Text = "deadline" }); db.Posts.Add(post); db.SaveChanges(); 25 "Code First" Approach in EF Live Demo Using Code First Migrations in EF Code First Migrations in Entity Framework

Enable Code First Migrations Open Package Manager Console Run Enable-Migrations command -EnableAutomaticMigrations for auto migrations 28 Using Code First Migrations in EF Live Demo

ORM Technologies and Entity Framework (EF) ? Qu ? s n o ti s e

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