Entity Framework Core 8

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Entity Framework Core Tools


# test if Entity Framework Core Tools has been installed
dotnet ef
# be sure to run the previous command in the folder of the project where EF has been added

# 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

# update
dotnet tool update dotnet-ef --global
# --version 7.0.14

Package Manager Console in Visual Studio

Visual Studio
  • View → Other Windows → Package Manager Console
  • Default Project = the one containing the entity configurations
  • Startup Project = the one containing the sql server configuration
# test if Entity Framework Core Tools has been installed
Get-Help about_EntityFrameworkCore

# install
Install-Package Microsoft.EntityFrameworkCore.Tools

# update
Update-Package Microsoft.EntityFrameworkCore.Tools

Add Entity Framework Core package

# sql server
dotnet add package Microsoft.EntityFrameworkCore.SqlServer

# mysql
dotnet add package Pomelo.EntityFrameworkCore.MySql
Microsoft.EntityFrameworkCore.Design allows to scaffold and has to be installed on the executed project.

Data Providers

Provider Package NuGet Connection String
SQL Server Microsoft.EntityFrameworkCore.SqlServer Server=(localdb)\\MSSQLLocalDB;Database=MyDb;Integrated Security=True;MultipleActiveResultSets=True;
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"
Sqlite Microsoft.EntityFrameworkCore.Sqlite Data Source=/tmp/file.db

Connection string

  • The connection string could be stored in the secret store in dev environnement
  • It could also be stored in appsettings.Development.json in dev environnement
  "ConnectionStrings": {
    "MariaDb": "server=localhost;database=test;user=test;password=***"

Dependency injection (ASP.Net Core)

By default the DbContext is registered as a scoped service: a new DbContext is created on a new thread for each API request.

MariaDb / MySql

var connectionString = builder.Configuration.GetConnectionString("MariaDb");  // get the connection string from the appsettings.json or the secret store
var serverVersion = new MariaDbServerVersion(new Version(10, 11, 4));

    dbContextOptions => dbContextOptions
        .UseMySql(connectionString, serverVersion));

SSL Authentication Error

On Windows, if named pipe authentication is used you may have this issue.
Disable SSL in the connection string to workaround it: sslmode=none

SQL Server


var connectionStringWithoutPassword = builder.Configuration.GetConnectionString("SqlServer");
var connectionStringBuilder = new SqlConnectionStringBuilder(connectionStringWithoutPassword);  // Package: System.Data.SqlClient
connectionStringBuilder.Password = builder.Configuration["SqlServerPassword"];
var connectionString = connectionStringBuilder.ConnectionString;

DbContext OnConfiguring

public class MyAppContext : DbContext
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        optionsBuilder.UseSqlServer("server=localhost;database=test;user=test;password=***"); // hard-coded connection string
        optionsBuilder.UseMySql("name=ConnectionStrings:MariaDb", ServerVersion.Parse("10.11.4-mariadb")); // get it from the appsettings.json or the secret storage
        optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["SqlServerConnectionString"].ConnectionString); // WPF

Log underlying SQL query

    options => options
        .LogTo(Console.WriteLine, LogLevel.Information)  // simple logging
        .UseLoggerFactory(LoggerFactory.Create(loggingBuilder =>
                .AddConfiguration(builder.Configuration.GetSection("Logging"))  // log the configuration
                .AddConsole()  // log into the console if there is one
                .AddDebug()))  // log into VS output Window and Linux journal
        .EnableSensitiveDataLogging(  // include the values of data in exception messages
            builder.Configuration.GetValue<bool>("DbContextLogOptions:EnableSensitiveDataLogging", false))
        .EnableDetailedErrors(        // wrap each call to read a value in a try-catch block
            builder.Configuration.GetValue<bool>("DbContextLogOptions:EnableDetailedErrors", false))
        .UseMySql(connectionString, serverVersion)
"DbContextLogOptions": {
  "EnableSensitiveDataLogging": true,
  "EnableDetailedErrors":  true

Database first: scaffold database to model entities

# generate entity classes and context class
dotnet ef dbcontext scaffold
  "Server=localhost;Database=MyDb;User=sa;Password=***;"  # an harcoded connection string
  "Name=ConnectionStrings:SqlServer"                      # get the connection string from the appsettings.json or the secret storage
  Microsoft.EntityFrameworkCore.SqlServer  # the database provider
  --output-dir DataAccess/Entities  # 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

Visual Studio

  • Ensure Entity Framework Core Tools have been installed
  • View → Other Windows → Package Manager Console
  • Default Project = the one containing the entity configurations ?
  • Startup Project = the one containing the sql server configuration ?
# SQL Server
Scaffold-DbContext 'Data Source=MY-PC;Initial Catalog=MyDb' Microsoft.EntityFrameworkCore.SqlServer -OutputDir Entities

# MariaDB
Scaffold-DbContext 'ConnectionStrings:MyConnectionString' Pomelo.EntityFrameworkCore.MySql -OutputDir DataAccess/Entities -ContextDir DataAccess -Context "BourseContext" -Force
Error Titre colonne 2
The certificate chain was issued by an authority that is not trusted Add Encrypt=False to the connection string
Login failed for user Add Integrated Security=True to the connection string

Custom Reverse Engineering Templates

Repository Pattern

  • 1 Repository per resource: ItemRepository
  • 1 DbContext for the whole application
public class ItemRepository : IItemRepository
    private readonly MyAppContext context;

    public ItemRepository(MyAppContext context)
        this.context = context;

    public async Task<IReadOnlyCollection<Item>> GetAllItemsAsync(CancellationToken cancellationToken)
        var items = await context.Items
            .Include(x => x.NavigationProperty)
        return items;

    public async Task<Item?> GetItemByIdAsync(int id, CancellationToken cancellationToken)
        var item = await context.Items
            .SingleOrDefaultAsync(x => x.Id == id, cancellationToken);
        return item;

    public async Task<IReadOnlyCollection<Item>> GetItemsByNameAsync(string name, CancellationToken cancellationToken)
        var items = await context.Items
            .Where(x => EF.Functions.Like(x.Name, $"%{name}%"))
        return items;

    public async Task<Item> CreateItemAsync(Item item, CancellationToken cancellationToken)
        await context.AddAsync(item, cancellationToken);
        await context.SaveChangesAsync(cancellationToken);
        return item; // it now contains its id

    public async Task<bool> UpdateItemAsync(int id, Item item, CancellationToken cancellationToken)

        var itemToUpdate = await context.Items.SingleOrDefaultAsync(x => x.Id == id, cancellationToken);

        if (itemToUpdate is null)
            return false; // send not found from controller then

        itemToUpdate.Name = item.Name;
        await context.SaveChangesAsync();
        return true;

    public async Task<bool> DeleteItemAsync(int id, CancellationToken cancellationToken)
        var nbAffectedRows = await context.Items.Where(x => x.Id == id).ExecuteDeleteAsync(cancellationToken);
        return nbAffectedRows == 1;

Generic repository

public abstract class RepositoryBase<TEntity, TCreateUpdateQuery> where TEntity : class, new()
    private readonly AppContext context;

    private DbSet<TEntity> dbEntities { get; }

    protected RepositoryBase(BourseContext context)
        this.context = context ?? throw new ArgumentNullException(nameof(context));
        dbEntities = this.context.Set<TEntity>();

    protected async Task<IReadOnlyCollection<TResult>> GetAsync<TResult>(
        Expression<Func<TEntity, TResult>> selector,
        Func<IQueryable<TEntity>, IIncludableQueryable<TEntity, object>>? include = null,
        Expression<Func<TEntity, bool>>? predicate = null,
        Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>? orderBy = null,
        Func<IQueryable<TEntity>, IQueryable<TEntity>>? skipTake = null,
        bool disableTracking = true,
        CancellationToken cancellationToken = default)
        where TResult : class
        IQueryable<TEntity> query = dbEntities;

        if (include is not null)
            query = include(query);

        if (predicate is not null)
            query = query.Where(predicate);

        if (orderBy is not null)
            query = orderBy(query);

        if (skipTake is not null)
            query = skipTake(query);

        if (disableTracking)
            query = query.AsNoTracking();

        return await query.Select(selector).ToListAsync(cancellationToken);

    public async Task<TEntity> CreateAsync(
        TEntity entity, CancellationToken cancellationToken)

        await context.AddAsync(entity, cancellationToken);
        await context.SaveChangesAsync(cancellationToken);
        return entity;

    public async Task<bool> UpdateAsync(
        Expression<Func<TEntity, bool>> filterByIdExpression,
        TCreateUpdateQuery query,
        CancellationToken cancellationToken)

        var entityToUpdate = await dbEntities
            .FirstOrDefaultAsync(filterByIdExpression, cancellationToken);

        if (entityToUpdate is null)
            return false;

        UpdateEntityFromCreateUpdateQuery(query, entityToUpdate);
        await context.SaveChangesAsync(cancellationToken);
        return true;

    public async Task<bool> DeleteAsync(
        Expression<Func<TEntity, bool>> filterByIdExpression,
        CancellationToken cancellationToken)
        var nbAffectedRows = await dbEntities

        return nbAffectedRows > 0;

Avoid using AsNoTracking and Include

AsNoTracking is used to improve performances when you don't need the entities to be tracked for changes. But a better way to improve performances is to use projection so you don't return the whole entity but only the needed fields. This way you don't need AsNoTracking because there is no more entities to track.
Include is used to retrieve other entities linked by a foreign key / navigation property. If you use a projection with a navigation property, you don't have to use Include.

Query generation

string contains vs like

context.Items.Where(x => x.Name.Contains("item1"));
SELECT [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE (@__query_Name_0 LIKE N'') OR (CHARINDEX(@__query_Name_0, [i].[Name]) > 0)
context.Items.Where(x => EF.Functions.Like(x.Name, "%item1%"));
SELECT [i].[Id], [i].[Name]
FROM [Items] AS [i]
WHERE [i].[Name] LIKE @__Format_1


context.Items.Any(x => x.Id == 1);
    SELECT 1
    FROM `item` AS `i`
    WHERE `i`.`id` = @__id_0)

left join

// with navigation property
context.Users.Select(u => new { u.Name, u.Group?.Name });

// method syntax
        user => user.GroupId,
        group => group.Id,
        (user, grouping) => new { user, grouping }
    .SelectMany(z => z.grouping.DefaultIfEmpty(), (z, grp) => new { userName = z.user.Name, groupName = grp.Name })
    .Select(x => new { x.userName, x.groupName });

// query syntax
from user in context.Users
join group in context.Groups
on user.GroupId equals group.Id into grouping
from grp in grouping.DefaultIfEmpty()
select new { userName = user.Name, groupName = grp.Name };
SELECT u.Name AS userName, g.Name AS groupName 
FROM User AS u
ON u.GroupId = g.Id


public async Task<IReadOnlyCollection<Item>> GetItemsAsync(ItemQuery query, CancellationToken cancellationToken)
    var items = await this.context.Items
        .Skip((query.PageIndex - 1) * query.PageSize)
    return items;