Entity Framework Core

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Description

  • Réécriture complète d'EF
  • Plus de nécessite d'utilisé des BdD relationnelles uniquement

Ajouter les packages au projet

Bash.svg
cd MyProject

# sql server
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Design

# mysql
dotnet add package Pomelo.EntityFrameworkCore.MySql
dotnet add package Microsoft.EntityFrameworkCore.Design --version 3.1.12
# Pomelo.EntityFrameworkCore.MySql 3.2.4 -> Microsoft.EntityFrameworkCore.Relational (>= 3.1.8 && < 5.0.0)

Data Providers

Provider Package NuGet Connection String
SQL Server Microsoft.EntityFrameworkCore.SqlServer Server=(localdb)\\MSSQLLocalDB;Database=MyDb;Integrated Security=True;MultipleActiveResultSets=True;
Server=localhost;Database=MyDb;User=sa;Password=pwd;
Sqlite Microsoft.EntityFrameworkCore.Sqlite Data Source=/tmp/file.db
MySQL / MariaDB Pomelo.EntityFrameworkCore.MySql server=localhost;database=MyDb;user=root;password=pwd
PostgreSQL Npgsql.EntityFrameworkCore.PostgreSQL Host=localhost;Database=MyDb;Username=root;Password=pwd
InMemory Microsoft.EntityFrameworkCore.InMemory databaseName: "test_database"

Entity Framework Core Tools

  • View → Other Windows → Package Manager Console
  • Default Project = the one containing the entity configurations
  • Startup Project = the one containing the sql server configuration
Powershell.svg
# tester si Entity Framework Core Tools est bien installé et fonctionnel
dotnet ef
# bien se mettre dans le dossier du projet
# faire un dotnet restore au cas où la restoration n'aurait pas fonctionnée

# dotnet ef must be installed as a global or local tool
dotnet tool install --global dotnet-ef
# installed in ~/.dotnet/tools
# Add ~/.dotnet/tools to PATH

# màj de dotnet-ef
dotnet tool update --global dotnet-ef

# ajouter le paquet nuget suivant
dotnet add package Microsoft.EntityFrameworkCore.Design

Create DbContext

DataAccess/MyAppContext.cs
public class MyAppContext : DbContext
{
    public DbSet<Item> Items => Set<Item>();
}

Configure entity types

Conventions
Target Convention
Primary key property named Id or <type_name>Id will be configured as the primary key of an entity with the name PK_<type_name>.
Foreign key a relationship will be created when there is a navigation property discovered on a type.
required property whose .NET type can contain null will be configured as optional, whereas properties whose .NET type cannot contain null will be configured as required.
Table name same name as the DbSet property that exposes the entity or same as class name.

Links:

EntityTypeConfiguration with Fluent API

DataAccess/DbModelConfiguration/ItemConfiguration.cs
internal sealed class ItemConfiguration : IEntityTypeConfiguration<Item>
{
    public void Configure(EntityTypeBuilder<Item> builder)
    {
        builder.ToTable("item");  // by convention same name as the DbSet property

        builder.Property(e => e.Id)
               .HasColumnName("id")  // bc same name as property name
               .HasColumnType("smallint")
               .ValueGeneratedOnAdd() // bc if the column is identified as the PK
               .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
        builder.HasKey(e => e.Id)  // bc a primary key is automatically generated on property named \w*Id
               .HasName("pk_item");  // bc PK_item

        builder.Property(e => e.Name)
               .HasColumnName("name")
               .HasMaxLength(50)  // varchar(50) CHARACTER SET utf8mb4
               .HasColumnType("nvarchar(50)")
               .HasCharSet("utf8mb4")  // if not specified the database character set and collation are used
               .HasCollation("utf8mb4_unicode_ci");
               .IsRequired();

        builder.Property(e => e.CreationDate)
               .HasColumnName("creation_date")
               .HasColumnType("date");

        builder.Property(e => e.Price)
               .HasColumnName("price")
               .HasColumnType("decimal(5,2)");

        builder.HasIndex(e => e.Name)
               .HasName("ix_item_name")
               .IsUnique();

        // foreign key
        builder.Property(e => e.GroupId)
               .HasColumnName("group_id")
               .HasColumnType("tinyint");

        builder.HasIndex(e => e.GroupId)
               .HasName("ix_items_group_id");

        builder.HasOne(e => e.Group)  // navigation property: Item.Group
               .WithMany(e => e.Items)  // with navigation property: Group.Items
               .WithMany()              // without navigation property: Group.Items
               .HasForeignKey(e => e.GroupId)  // foreign key property: Item.GroupId
               .OnDelete(DeleteBehavior.ClientSetNull)
               .HasConstraintName("fk_items_groups_group_id");
Unsigned types are not supported.
DataAccess/ItemContext.cs
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // specify the configuration
    modelBuilder.ApplyConfiguration(new ItemConfiguration());

    // look for EntityTypeConfiguration in the current assembly
    modelBuilder.ApplyConfigurationsFromAssembly(typeof(ItemContext).Assembly);
}

Data Annotations Attributes

Data/Entities/Item.cs
// définit le nom de la table, par défaut le nom de la classe est utilisées
[Table("Items")]
public class Item
{
    public int Id { get; set; }
    [Column("My_Name")]  // mapping
    public string Name { get; set; }
    // définit le type SQL qui sera utilisé pour le stockage de la donnée, ici un décimal de 7 chiffres dont 2 après la virgule
    [Column(TypeName = "decimal(7, 2)")]
    public decimal Price { get; set; }
    [Column(TypeName = "date")]
    public DateTime Date { get; set; }
}

Nécessite le package nuget System.ComponentModel.DataAnnotations

Vue / view

Model/BlogPostsCount.cs
public class BlogPostsCount
{
    public int BlogId { get; set; }
    public int PostCount { get; set; }
}
Model/Configuration/BlogPostsCountConfiguration
public class BlogPostsCountConfiguration : IEntityTypeConfiguration<BlogPostsCount>
{
    public void Configure(EntityTypeBuilder<BlogPostsCount> builder)
    {
        builder.ToView("View_BlogPostCounts");
        builder.HasKey(x => x.BlogId);
    }
}
Model/BloggingContext.cs
public class BloggingContext : DbContext
{
    public DbSet<BlogPostsCount> BlogPostCounts { get; set; }
Bash.svg
# create a new migration
dotnet ef migrations add View_BlogPostCounts
Migration/YYYYMMDDHHmmss_View_BlogPostCounts.cs
public partial class View_BlogPostCounts : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.Sql(
            @"CREATE VIEW View_BlogPostCounts AS
            SELECT b.BlogId, Count(p.PostId) as PostCount
            FROM Blogs b
            JOIN Posts p on p.BlogId = b.BlogId
            GROUP BY b.BlogId;");
    }

    protected override void Down(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.Sql("DROP VIEW View_BlogPostCounts;");
    }
}
Bash.svg
# update the database
dotnet ef database update
Controllers/BlogController.cs
[HttpGet]
public async Task<IEnumerable<BlogDto>> Get()
{
    var query = from b in this.dbContext.Blogs
                join c in this.dbContext.BlogPostCounts
                on b.BlogId equals c.BlogId
                select new BlogDto
                {
                    BlogId = b.BlogId,
                    Url = b.Url,
                    PostsCount = c.PostCount,
                    Posts = b.Posts.Select(y => new PostDto
                    {
                        PostId = y.PostId,
                        Title = y.Title,
                        Content = y.Content
                    })
                };
                    
    var dto = await query.ToListAsync();

QueryType

Data/MyAppContext.cs
public class MyAppContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Query<MyQueryType>().ToView("MyView");

Connection string

DbContext OnConfiguring

DataAccess/MyAppContext.cs
public class MyAppContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("server=localhost;database=test;user=test;password=****");
        optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["SqlServerConnectionString"].ConnectionString); // WPF
    }
}

Constructor parameter

Csharp.svg
var builder = new ConfigurationBuilder()
    .AddUserSecrets<MyAppContextFactory>();
var configuration = builder.Build();

var connectionStringBuilder = new SqlConnectionStringBuilder("server=localhost;database=test;user=test;");
connectionStringBuilder.Password = configuration["DbPassword"];

var connectionString = connectionStringBuilder.ConnectionString;
var connectionString = "server=localhost;database=test;user=test;password=****";

var contextOptions = new DbContextOptionsBuilder<MyAppContext>()
    .UseMySql(
        connectionString,
        mySqlOptions => mySqlOptions.ServerVersion("10.5.8-mariadb"))
    .Options;

using var context = new MyAppContext(contextOptions);
DataAccess/MyAppContext.cs
public class MyAppContext : DbContext
{
    public MyAppContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    { }

Dependency injection (ASP.Net Core)

Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    // SQL Server
    var builder = new SqlConnectionStringBuilder(Configuration.GetConnectionString("SqlServer")); // read the appsettings.json
    builder.Password = Configuration["DbPassword"]; // use the Secret Manager in dev, and an environment variable in prod
    services.AddDbContext<MyAppContext>(options =>
        options.UseSqlServer(builder.ConnectionString)
    );

    // MySql
    services.AddDbContext<MyAppContext>(options =>
        options.UseMySql(
            Configuration.GetConnectionString("MySql"),
            mySqlOptions => mySqlOptions.ServerVersion(
                new ServerVersion(new Version(10, 5, 8),
                ServerType.MariaDb)));
            // mySqlOptions => mySqlOptions.ServerVersion("10.5.8-mariadb");
    );

    // In Memory
    services.AddDbContext<MyAppContext>(options =>
        options.UseInMemoryDatabase("WebApplicationCoreMemoryDb");
    );
DataAccess/MyAppContext.cs
public class MyAppContext : DbContext
{
    // permet de passer des options à la construction du DbContext
    public MyAppContext(DbContextOptions<MyAppContext> options) : base(options)
    { }
MyController.cs
public class MyController
{
    private readonly MyAppContext context;

    public MyController(MyAppContext context)
    {
        this.context = context;
    }

Design time DbContext factory

  • Explain how to create a Context which doesn't have a parameterless ctor.
  • Separate the EF code needed for generating database tables at design-time from EF code used by your application at runtime.
DataAccess/MyAppContextFactory
public class MyAppContextFactory : IDesignTimeDbContextFactory<MyAppContext>
{
    private string connectionString;

    public MyAppContextFactory()
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json")
            .AddUserSecrets<MyAppContextFactory>();  // read stored secrets
        var configuration = builder.Build();

        connectionString = configuration.GetConnectionString("SqlServer");
    }

    public MyAppContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<MyAppContext>();
        builder.UseSqlServer(connectionString);
        var dbContext = new MyAppContext(builder.Options);
        return dbContext;
    }
}
DataAccess/MyAppContext.cs
public class MyAppContext : DbContext
{
    // permet de passer des options à la construction du DbContext
    public MyAppContext(DbContextOptions<MyAppContext> options) : base(options)
    { }
Csharp.svg
var dbContextFactory = new MyAppContextFactory();
using var dbContext = dbContextFactory.CreateDbContext(args);

Migrations

Powershell.svg
# création du fichier de migration
dotnet ef migrations add InitialCreate
# un fichier YYYYMMDDHHMMSSS_IntialCreate.cs est créé dans le dossier Migration

# supprimer la dernière migration
dotnet ef migrations remove

# lister les migration
dotnet ef migrations list

# il faut créer une migration avant de pouvoir passer à la génération

# génération d'un script SQL pour voir ce que va faire la migration
dotnet ef migrations script <FROM> <TO>
# From: 0 par défaut
# To: dernière migration par défaut

# génération et exécution du script SQL
dotnet ef database update

# revert the last already applied migration
dotnet ef database update <previous-migration-to-keep>
dotnet ef migrations remove

Add data update during migration

After having added a migration, you can edit the Migrations/YYYYMMDDHHmmss_MigrationName.cs file:

Migrations/YYYYMMDDHHmmss_MigrationName.cs
public partial class MigrationName : Migration
{
    protected override void Up(MigrationBuilder migrationBuilder)
    {
        /* ... */

        // update data
        migrationBuilder.UpdateData(
            table: "MyTable",
            keyColumn: "Id",
            keyValue: 1,
            column: "Column1",
            value: 1);

        // execute SQL command
        migrationBuilder.Sql("UPDATE `MyTable` SET `Column1` = `Column2`;");
    }

Apply migrations at runtime

ASP.Net web API

Startup.cs
public static void Configure(IApplicationBuilder app, IWebHostEnvironment env, MyDbContext context)
{
    // ensures your existing migrations are applied to the database, create it if needed
    context.Database.Migrate();

    // create the db if it doesn't exist
    context.Database.EnsureCreated();
}
EnsureCreated totally bypasses migrations and just creates the schema for you, you can't mix this with migrations.

EnsureCreated is designed for testing or rapid prototyping where you are ok with dropping and re-creating the database each time.

If you are using migrations and want to have them automatically applied on app start, then you can use Migrate instead.

Data Seeding

Permet de remplir la bdd avec un jeu initial de données.

Data/MyAppContext.cs
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Item>().HasData(
        new Item { Id = 1, Name = "Item1" },
        new Item { Id = 2, Name = "Item2" }
    );
}
  • set the ids even if they belong to an auto-incremented column
  • Use the ids to link objects.

OLD

Data/MyAppSeeder.cs
public class MyAppSeeder
{
    private readonly MyAppContext _context;

    public MyAppSeeder(MyAppContext context)
    {
        _context = context;
    }

    public void Seed()
    {
        _context.Database.EnsureCreated();

        if (!_context.Items.Any())
        {
            _context.Items.Add(new Item() { Name = "Item 1" });  // ne pas définir l'Id
            _context.Items.Add(new Item() { Name = "Item 2" });
            _context.SaveChanges();
        }
Sartup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<MyAppSeeder>();
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    using (var scope = app.ApplicationServices.CreateScope())
    {
        var seeder = scope.ServiceProvider.GetService<MyAppSeeder>();
        seeder.Seed();
    }
}

Log underlying SQL query

Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<AppContext>(options =>
        options.UseLoggerFactory(LoggerFactory.Create(builder => builder.AddConsole()))
               .UseSqlServer(Configuration.GetConnectionString("SqlServer"))
    );
It will log in the Visual Studio Code Debug Console.
Program.cs
protected override void OnConfiguring(DbContextOptionsBuilder options)
{
    // log in addition in the Console
    options.LogTo(Console.WriteLine);

Database first: scaffold database to model entities

Bash.svg
# generate entity classes and context class
dotnet ef dbcontext scaffold "Server=localhost;Database=MyDb;User=sa;Password=pwd;" Microsoft.EntityFrameworkCore.SqlServer
    --output-dir Model             # output folder for entities
    --context-dir DataAccess       # output folder for DbContext
    --context "MyDbContext"        # default context name: DbNameContext
    --force                        # overwrite all the class files
    --table table1 --table table2  # scaffold only table1 and table2

Repository Pattern

  • 1 Repository par classe: ItemsRepository
  • 1 DbContext pour toute l'application
Data/ItemsRepository.cs
public class ItemsRepository : IItemsRepository
{
    private readonly MyAppContext context;

    public ItemsRepository(MyAppContext context)
    {
        this.context = context;
    }

    public async Task<IReadOnlyList<Item>> GetAllAsync()
    {
        return await context.Set<Item>()
                            .Include(x => x.SubClass)
                            .ToListAsync();
    }

    public async Task<Item> GetByIdAsync(int id)
    {
        var item = await context.FindAsync<Item>(id);
        // use Include with Find
        this.context.Entry(item).Reference(x => x.User).Load();
        return item;
    }

    public async Task<Item> CreateAsync(Item item)
    {
        var createdItemEntry = await context.AddAsync(item);
        await context.SaveChangesAsync();
        return createdItemEntry.Entity;
    }

    public async Task UpdateAsync(Item itemToUpdate, Item item)
    {
        itemToUpdate.Name = item.Name;
        await context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Item item)
    {
        context.Remove(item);
        await context.SaveChangesAsync();
    }
}

La création d'une interface permettra d'utiliser d'autres sources de données pour faire des tests.

Data\IItemsRepository.cs
public interface IItemsRepository
{
    Task<IReadOnlyList<Item>> GetAllAsync();
    Task<Item> GetByIdAsync(int id);
    Task<Item> CreateAsync(Item item);
    Task UpdateAsync(Item itemToUpdate, Item item);
    Task DeleteAsync(Item item);
}
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IItemsRepository, ItemsRepository>();

Include

Csharp.svg
await this.dbContext.Blogs
                    .Include(x => x.Posts) // load Blog.Posts
                    // .ThenInclude(x => x.AnotherProperty)
                    .ToListAsync();
Tsql.svg
SELECT [b].[BlogId], [b].[Url], [p].[PostId], [p].[BlogId], [p].[Content], [p].[Title]
FROM [Blogs] AS [b]
LEFT JOIN [Posts] AS [p] ON [b].[BlogId] = [p].[BlogId]
ORDER BY [b].[BlogId], [p].[PostId]

Datetime

Csharp.svg
this.context.Item
    .Where(x => EF.Functions.DateDiffDay(x.Date2, x.Date1) > 0)
    .ToListAsync();

N+1 selects problem

EF fait ses requêtes en lazy loading, ce qui veut dire que les requêtes SQL ne sont exécutées que lorsqu'on a besoin des données.

Csharp.svg
// 1 requête pour récupérer tous les contacts
IEnumerable<Contact> allContacts = context.Contacts;
foreach (var contact in allContacts)
{
    // pour récupérer l'age de chaque contact il faut faire une nouvelle requête pour chaque contact
    // ce qui donne de mauvaises performances
    if (contact.age > 30) { /* ... */ }
}

// inclure Age lors de la récupération des contacts
// ainsi tous se fait en une seule requête
IEnumerable<Contact> allContacts = context.Contacts.Include(c => c.Age);

Executing Raw SQL Queries

Csharp.svg
using System.Data.SqlClient;  // pour SqlParameter

var books = context.Books.FromSql("SELECT Id, Title FROM Books").ToList();

// passage de paramètre avec l'interpolation de string
var book = context.Books.FromSql($"SELECT Id, Title FROM Books WHERE Title = {title}").FirstOrDefault();

// passage de paramètre avec DbParameter
var p1 = new SqlParameter("@Id", id);
var book = db.Books.FromSql("SELECT * FROM Books WHERE Id = @Id", p1).FirstOrDefault();

// opérations INSERT, UPDATE, DELETE
var commandText = "INSERT Authors (AuthorName) VALUES (@AuthorName)";
var name = new SqlParameter("@AuthorName", "Jean-Christophe Grangé");
context.Database.ExecuteSqlCommand(commandText, name);

// procédure stockée
var authorId = new SqlParameter("@AuthorId", 1);
var books = context.Books.FromSql("EXEC GetBooksByAuthor @AuthorId" , authorId).ToList();

// procédure stockée avec plusieurs paramètres
var parameters = new List<SqlParameter>();
parameters.Add(new SqlParameter(name, SqlDbType.Int) { Value = (object)value?.ToInt32(CultureInfo.InvariantCulture) ?? DBNull.Value });
var parameterNamesList = string.Join(", ", parameters.Select(p => p.ParameterName));
var storedProcedureResultRows = await context.Database.SqlQuery<StoredProcedureResultRow>(
    $"{StoredProcedureName} {parameterNamesList}",
    parameters.Cast<object>().ToArray()).ToListAsync(cancellationToken);

Pagination

Csharp.svg
private const int PageSize = 10;

public async Task<IReadOnlyList<Item>> GetAsync(int pageIndex)
{
    var items = await this.context.Item
                                  .AsNoTracking()
                                  .Skip((pageIndex - 1) * PageSize)
                                  .Take(PageSize)
                                  .ToListAsync();
    return items;
}

Ignore accent in string comparaison (MySql - Pomelo)

Use the like operator.

Csharp.svg
// doesn't return Nicolàs
person.Where(x => x.Name.Contains("Nicolas", StringComparison.CurrentCultureIgnoreCase));

// return Nicolàs
person.Where(x => EF.Functions.Like(x.Name, "%Nicolas%"));

Inheritance

Table Per Hierarchy

By default, EF maps the inheritance using the table-per-hierarchy (TPH) pattern.
TPH uses a single table to store the data for all types in the hierarchy, and a discriminator column is used to identify which type each row represents.

Id Discriminator OwnerId BorrowerId
1 SimpleItem Paul null
2 BorrowedItem Jean Luc
ItemBase.cs
public abstract class ItemBase
{
    public int Id { get; set; }
    public ItemType Type { get; set; }
    public int OwnerId { get; set; }
    public Person Owner { get; set; }
}
SimpleItem.cs
public class SimpleItem : ItemBase
{ }
BorrowedItem.cs
public class BorrowedItem : ItemBase
{
    public int BorrowerId { get; set; }
    public Person Borrower { get; set; }
}
ItemContext.cs
public class ItemContext : DbContext
{
    public DbSet<ItemBase> Item { get; set; }
    public DbSet<SimpleItem> SimpleItem { get; set; }
    public DbSet<BorrowedItem> BorrowedItem { get; set; }

Examples

One to one relationship

One Address per User.

Csharp.svg
public class Address
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string City { get; set; }
    public User User { get; set; }
}

public class User
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    public Address Address { get; set; }
    public int AddressId { get; set; }
}

public class MyAppContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // allow to have both User.Address and Address.User
        modelBuilder.Entity<Address>()
                    .HasOne(x => x.User)
                    .WithOne(user => user.Address)
                    .HasForeignKey<User>(x => x.AddressId);
Tsql.svg
CREATE TABLE [Addresses] (
    [Id] int NOT NULL IDENTITY,
    [City] nvarchar(40) NOT NULL,
    CONSTRAINT [PK_Addresses] PRIMARY KEY ([Id])
);

CREATE TABLE [Users] (
    [Id] int NOT NULL IDENTITY,
    [Name] nvarchar(40) NOT NULL,
    [AddressId] int NOT NULL,
    CONSTRAINT [PK_Users] PRIMARY KEY ([Id]),
    CONSTRAINT [FK_Users_Addresses_AddressId] FOREIGN KEY ([AddressId]) REFERENCES [Addresses] ([Id]) ON DELETE CASCADE
);

CREATE UNIQUE INDEX [IX_Users_AddressId] ON [Users] ([AddressId]);

One to many relationship

Many Task per User.

Csharp.svg
public class User
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    public Task[] Tasks { get; set; }  // can be remove without changing the generated sql if Task.User exists
}

public class Task
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    [Required]
    public User User { get; set; }  // can be remove without changing the generated sql if User.Tasks exists
}

public class MyAppContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
                    .HasMany(x => x.Tasks)
                    .WithOne(task => task.User);
Tsql.svg
CREATE TABLE [Users] (
    [Id] int NOT NULL IDENTITY,
    [Name] nvarchar(40) NOT NULL,
    CONSTRAINT [PK_Users] PRIMARY KEY ([Id])
);

CREATE TABLE [Task] (
    [Id] int NOT NULL IDENTITY,
    [Name] nvarchar(40) NOT NULL,
    [UserId] int NOT NULL,
    CONSTRAINT [PK_Task] PRIMARY KEY ([Id]),
    CONSTRAINT [FK_Task_Users_UserId] FOREIGN KEY ([UserId]) REFERENCES [Users] ([Id]) ON DELETE CASCADE
);

CREATE INDEX [IX_Task_UserId] ON [Task] ([UserId]);

Many to many relationship

Many User per Group and many Group per User.

Short way

Csharp.svg
public class Group
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    public IReadOnlyCollection<User> Users { get; set; }
}

public class User
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    public IReadOnlyCollection<User> Groups { get; set; }
}

public class MyAppContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // seed
        var users = new [] { new User { Id = 1, Name = "User1" } };
        modelBuilder.Entity<User>().HasData(users);

        var groups = new [] { new Group { Id = 1, Name = "Group1" } };
        modelBuilder.Entity<Group>().HasData(groups);

        var userGroups = new [] { new { UserId = 1, GroupId = 1 } };
        modelBuilder.Entity<User>()
                    .HasMany(x => x.Groups)
                    .WithMany(x => x.Users)
                    .UsingEntity(x => x.HasData(userGroups));
    }
}

// query
var users = await context.Users
                         .Include(x => x.Groups)
                         .ToListAsync();

Detailed way

Csharp.svg
public class Group
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    public UserGroup[] UserGroups { get; set; }
}

public class User
{
    public int Id { get; set; }
    [Required, StringLength(40)]
    public string Name { get; set; }
    [Required]
    public Address Address { get; set; }
    public Task[] Tasks { get; set; }
    public UserGroup[] UserGroups { get; set; }
}

public class UserGroup
{
    public int UserId { get; set; }
    public User User { get; set; }
    public int GroupId { get; set; }
    public Group Group { get; set; }
}

public class MyAppContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<UserGroup>()
                    .HasKey(x => new { x.UserId, x.GroupId });
        modelBuilder.Entity<UserGroup>()
                    .HasOne(x => x.User)
                    .WithMany(user => user.UserGroups)
                    .HasForeignKey(x => x.UserId);
        modelBuilder.Entity<UserGroup>()
                    .HasOne(x => x.Group)
                    .WithMany(group => group.UserGroups)
                    .HasForeignKey(x => x.GroupId);

        // seed
        var users = new [] { new User { Id = 1, Name = "User1" } };
        modelBuilder.Entity<User>().HasData(users);

        var groups = new [] { new Group { Id = 1, Name = "Group1" } };
        modelBuilder.Entity<Group>().HasData(groups);

        var userGroups = new [] { new UserGroup { UserId = 1, GroupId = 1 } };
        modelBuilder.Entity<UserGroup>().HasData(userGroups);
    }
}

// query
var users = await context.Users
                         .Include(x => x.UserGroups)
                         .ThenInclude(x => x.Group)
                         .ToListAsync();

Unit tests

Use the InMemory database provider to test the repositories and the services.

MyServiceTest.cs
private DbContextOptions<MyContext> options;

public MyServiceTest()
{
    options = new DbContextOptionsBuilder<MyContext>()
        .UseInMemoryDatabase(databaseName: "test")
        .Options;

    // Insert seed data into the database using one instance of the context
    using (var context = new MyContext(options))
    {
        context.Database.EnsureDeleted();
        context.Database.EnsureCreated();

        var entity = new MyEntity { Id = 1 };
        context.MyEntity.Add(expense);
        context.SaveChanges();
    }
}

[Fact]
public async Task MyMethodAsync_Input_Output()
{
    // Use a clean instance of the context to run the test
    using (var context = new MyContext(options))
    {
        var repository = new MyRepository(context);

        var service = new MyService(repository);

        var result = await service.MyMethod();

        Assert.Collection(
            result,
            item => Assert.Equal(1, item.Id));
    }
}

Erreurs

Cannot authenticate using Kerberos

Erreur sur Linux durant l'exécution de dotnet ef database update. Impossible de se connecter au serveur SQL.
Passer Trusted_Connection à False et ajouter le user et password à la connection string corrige le problème.

appsettings.json
"ConnectionStrings": {
    "DefaultConnection": "Server=localhost;Database=MyDb;Trusted_Connection=False;MultipleActiveResultSets=true;User=sa;Password=xxx"
  },

Specified key was too long; max key length is 767 bytes

Les index InnoDB (MySQL) ont une taille limitée. Il faut donc limité la taille des index à la création de la bdd.

Data/MyAppContext.cs
protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder); 

    // Shorten key length for Identity
    builder.Entity<IdentityRole>(entity => {
        entity.Property(m => m.NormalizedName).HasMaxLength(127);
    });
    builder.Entity<IdentityUser>(entity => {
        entity.Property(m => m.NormalizedUserName).HasMaxLength(127);
    });
}

The host localhost does not support SSL connections

Ajouter SslMode=none à la ConnectionString MySQL.

OLD - No executable found matching command "dotnet-ef"

Installer les packages Nuget:

  • Microsoft.EntityFrameworkCore.Tools
  • Microsoft.EntityFrameworkCore.Tools.DotNet

MyProject.csproj
<Project Sdk="Microsoft.NET.Sdk">
  <!-- Ajouter le groupe suivant -->
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.0.0" />
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0" /> 
  </ItemGroup>
Bash.svg
dotnet restore

Examples of generated queries

left join

Csharp.svg
context.Users.Select(u => new { u.Group, u });

from user in context.Users
join grp in context.Groups
on user.GroupId equals grp.Id into grouping
from grp in grouping.DefaultIfEmpty()
select new { grp, user };
Tsql.svg
SELECT [g].[Id], [g].[Name], [u].[Id], [u].[GroupId], [u].[Name]
FROM [User] AS[u]
LEFT JOIN [Group] AS [g] ON [u].[GroupId] = [g].[Id]

inner join

Csharp.svg
from user in context.Users
join grp in context.Groups
on user.GroupId equals grp.Id
select new { grp, user };
Tsql.svg
SELECT [g].[Id], [g].[Name], [u].[Id], [u].[GroupId], [u].[Name]
FROM [User] AS[u]
INNER JOIN [Group] AS [g] ON [u].[GroupId] = [g].[Id]

cross join

Csharp.svg
from grp in context.Groups
from user in context.Users
select new { grp, user };
Tsql.svg
SELECT [g].[Id], [g].[Name], [u].[Id], [u].[GroupId], [u].[Name]
FROM [Group] AS [g]
CROSS JOIN [User] AS [u]

find

Csharp.svg
var item = await context.Items.FindAsync(id);
Tsql.svg
SELECT TOP(1) [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE [i].[Id] = @__p_0

where

Csharp.svg
context.Items.Where(x => x.Name == "Item1");
Tsql.svg
SELECT [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE [i].[Name] = @__query_Name_0

string contains

Csharp.svg
context.Items.Where(x => x.Name.Contains("Item"));
Tsql.svg
SELECT [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE (@__query_Name_0 LIKE N'') OR (CHARINDEX(@__query_Name_0, [i].[Name]) > 0)

like

Csharp.svg
context.Items.Where(x => EF.Functions.Like(x.Name, "%Item%"));
Tsql.svg
SELECT [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE [i].[Name] LIKE @__Format_1

int contains

Csharp.svg
context.Items.Where(x => ids.Contains(x.Id));
Tsql.svg
SELECT [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE [i].[Id] IN (1, 2)

many to many

Csharp.svg
context.Items.Include(x => x.Categories).ToListAsync();
Tsql.svg
SELECT [i].[Id], [i].[Name], [t].[CategoriesId], [t].[ItemsId], [t].[Id], [t].[Name]
FROM [Items] AS [i]
LEFT JOIN (
    SELECT [c].[CategoriesId], [c].[ItemsId], [c0].[Id], [c0].[Name]
    FROM [CategoryItem] AS [c]
    INNER JOIN [Categories] AS [c0] ON [c].[CategoriesId] = [c0].[Id]
) AS [t] ON [i].[Id] = [t].[ItemsId]
ORDER BY [i].[Id], [t].[CategoriesId], [t].[ItemsId], [t].[Id]

update without fetch

Csharp.svg
// create a new item
var itemToUpdate = new Item { Id = 1, Name = "new name" }
// attach it then mark the property as modified
context.Attach(itemToUpdate).Property(x => x.Name).IsModified = true;

await context.SaveChangesAsync();
Tsql.svg
UPDATE [Items]
SET [Name] = @p0
WHERE [Id] = @p1;

Entity Framework Plus

Batch update

Csharp.svg
context.Items.Where(x => ids.Contains(x.Id))
             .UpdateAsync(x => new Item { Name = "new name" },
                          x =>
                          {
                              x.Executing = command => Console.WriteLine(command.CommandText);
                          });
Tsql.svg
UPDATE A 
SET A.[Name] = @zzz_BatchUpdate_0
FROM [Items] AS A
INNER JOIN (
  SELECT [i].[Id], [i].[Name]
  FROM [Items] AS [i]
  WHERE [i].[Id] IN (1, 2)
) AS B
ON A.[Id] = B.[Id]
  • Updates multiples rows
    • in a single database roundtrip
    • without loading entities in the context

Limitations:

  • Do not support Complex Type
  • Do not support TPC
  • Do not support TPH
  • Do not support TPT

If you need to use one of this feature, you need to use the paying library Entity Framework Extensions

Batch delete

  • Deletes multiples rows
    • in a single database roundtrip
    • without loading entities in the context

Query Future

Allow to reduce database roundtrip by batching multiple queries in the same sql command.

Csharp.svg
var futureItems = dbContext.Items.Future();
var futureCategories = dbContext.Categories.Future();

// TRIGGER all pending queries (futureItems & futureCategories)
var items = await futureItems.ToListAsync();

// for immediate methods (count, first, single, contains, any), use a query Deferred
var futureItemCount = await context.Items.DeferredCount().FutureValue();
var count = futureItemCount.Value;

Query cache

Csharp.svg
var items = await context.Items.FromCacheAsync();
// The first call perform a database round trip
// The following calls will take the value from the memory instead

// for immediate methods (count, first, single, contains, any), use a query Deferred
var count = await context.Items.DeferredCount().FromCacheAsync();

Audit

Allow to easily track changes, exclude/include entity or property and auto save audit entries in the database.