Migrating from EF6 to EF Core: What You Need to Know

Migrating from Entity Framework 6 (EF6) to Entity Framework Core (EF Core) can be a challenging task, but it also provides significant benefits such as performance improvements, cross-platform support, and improved testing capabilities. Here are some things you need to know when migrating from EF6 to EF Core:

1. Change in Namespace and Package Names: EF Core is a new implementation of the Entity Framework, and it has a different namespace and package name than EF6. When migrating, you will need to update your namespaces, and package references to use the new names.

2. Different API: EF Core has a different API than EF6. While many of the core concepts are the same, some of the method names and behaviors are different. You may need to update your code to use the new API.

3. No Lazy Loading by Default: In EF Core, lazy loading is not enabled by default. You will need to explicitly enable it by using the Microsoft.EntityFrameworkCore.Proxies package and adding .UseLazyLoadingProxies() to your DbContext configuration.

4. No Support for Some Data Providers: EF Core supports many data providers, but it does not support all the data providers that EF6 does. If you are using a data provider that is not supported by EF Core, you will need to find an alternative solution.

5. Different LINQ Implementation: EF Core has a different LINQ implementation than EF6. Some of the methods behave differently, and some of the methods are not available in EF Core. You may need to update your LINQ queries to use the new implementation.

6. Different Relationship Fix-up Behavior: EF6 automatically fixed up relationships when entities were added to the context. EF Core does not do this by default. Instead, you will need to manually fix up relationships by setting the navigation properties.

7. Different Migration System: EF Core has a different migration system than EF6. You will need to use the dotnet ef CLI tool to create and apply migrations.

8. Different Connection String Format: The connection string format in EF Core is different than in EF6. You will need to update your connection strings to use the new format.

9. Improved Performance: EF Core is generally faster than EF6, especially for read-heavy workloads. This is because it has a smaller memory footprint and uses compiled LINQ queries.

10. Improved Testing Capabilities: EF Core makes it easier to write tests because it has in-memory database providers and easier ways to mock the database.

Overall, migrating from EF6 to EF Core requires some effort, but it provides significant benefits, including improved performance and testing capabilities.

Here are some important point with example:

1. Different Namespace and Package Names:

       In EF6, the namespace for the Entity Framework is System.Data.Entity. In EF Core, the namespace is                Microsoft.EntityFrameworkCore.

       To install the EF Core packages using NuGet, you would use the following command:

     Install-Package Microsoft.EntityFrameworkCore

2. Different API:

        In EF6, you might write a query like this to retrieve all customers:

var customers = dbContext.Customers.ToList();

        In EF Core, the same query would be written like this:

var customers = await dbContext.Customers.ToListAsync();

        Note that in EF Core, the ToListAsync method is asynchronous.

3. No Lazy Loading by Default:

        In EF6, you can enable lazy loading like this:

public class MyContext : DbContext
{
    public MyContext()
    {
        this.Configuration.LazyLoadingEnabled = true;
    }
}

       In EF Core, you need to install the Microsoft.EntityFrameworkCore.Proxies package and configure

       your context like this:

public class MyContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseLazyLoadingProxies();
    }
}

4. Different LINQ Implementation:

     var customers = dbContext.Customers.Where(c => c.Name.Contains("John")).ToList();

     In EF Core, the same query would be written like this:

    var customers = await dbContext.Customers.Where(c => c.Name.Contains("John")).ToListAsync();

     Note that in EF Core, the ToListAsync method is asynchronous.

5. Different Relationship Fix-up Behavior:

    In EF6, you might add a new order for a customer like this:

    var customer = dbContext.Customers.FirstOrDefault(c => c.Id == customerId);
    var order = new Order { Customer = customer, Date = DateTime.Now };
    dbContext.Orders.Add(order);
    dbContext.SaveChanges();

    In EF Core, you would need to manually set the navigation property like this:

    var customer = await dbContext.Customers.FirstOrDefaultAsync(c => c.Id == customerId);
    var order = new Order { Date = DateTime.Now };
    customer.Orders.Add(order);
    await dbContext.SaveChangesAsync();

6. Different Migration System:

       In EF6, you would use the Add-Migration and Update-Database commands in the Package Manager

       Console to create and apply migrations.

       In EF Core, you would use the dotnet ef migrations add and dotnet ef database update commands

       in the command prompt to create and apply migrations.

7. Improved Testing Capabilities:

        In EF6, you might write a test like this to test your database context:

[TestClass]
public class MyContextTests
{
    [TestMethod]
    public void TestCustomers()
    {
        var dbContext = new MyContext();
        var customers = dbContext.Customers.ToList();
        Assert.IsTrue(customers.Count > 0);
    }
}

        In EF Core, you can use an in-memory database provider to write tests like this:

[TestClass]
public class MyContextTests
{
    [TestMethod]
    public async Task TestCustomers()
    {
        var options = new DbContextOptionsBuilder<MyContext>()
            .UseInMemoryDatabase(databaseName: "TestCustomers")
            .Options;

        using (var dbContext = new MyContext(options))
        {
            dbContext.Customers.Add(new Customer { Name = "John" });
            dbContext.Customers.Add(new Customer { Name = "Jane});