EF Core 2.0 new features

2.0.0-priview1-final, so this article is mainly about some instructions for this version.

mysql tutorial"

// 安装
PM> install-package Microsoft.EntityFrameworkCore.SqlServer -Pre -Version 2.0.0-preview1-final

// 升级
PM> update-package Microsoft.EntityFrameworkCore.SqlServer -Pre -Version 2.0.0-preview1-final

// 直接修改 CSPROJ 文件
<ItemGroup>
   <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" 
       Version="2.0.0-preview1-final" />
</ItemGroup>

// 或者通过以下命令
PM> update-package Microsoft.EntityFrameworkCore.Tools -Pre -Version 2.0.0-preview1-final

• Avoid creating unnecessary subqueries

• Some commands will switch to the client for execution

• Only a few requests will retrieve all columns of the table

• Sometimes without appropriate filter conditions, a single LINQ query is converted into N+1 queries.

var aCustomers =
    from c in context.Customers
    where EF.Functions.Like(c.Name, "a%");
    select c;

modelBuilder.Entity<Customer>()
    .OwnsOne(c => c.WorkAddress);public class Customer
{    public int CustomerId { get; set; }    public Address WorkAddress { get; set; }
}public class Address
{    public string Line { get; set; }    public string PostalOrZipCode { get; set; }    public string StateOrProvince { get; set; }    public string CityOrTown { get; internal set; }
}

Customer and Address will be generated as one table.

public class BloggingContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }
    public DbSet<Post> Posts { get; set; }

    public int TenantId {get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Post>()
            .HasQueryFilter(p => !p.IsDeleted &&
                  p.TenantId == this.TenantId );
    }
}

Include()). Of course you can use IgnoreQueryFilters() to disable this global filter in the query.

on every request. In EF Core 2.0, a new way of injecting a custom DbContext is introduced, which explicitly uses an instance pool to inject it into the container.

services.AddDbContextPool<BloggingContext>(
    options => options.UseSqlServer(connectionString));

Using this method, when the Controller requests a DbContext instance, it will first check whether there is an available instance in the pool. Once the request is processed, any state attached to the instance will be reset. , and then the instance is returned to the pool.

This concept is somewhat similar to the database connection pool in ADO.NET, which has the advantage of saving the cost of initializing a DbContext instance. Many ASP.NET Core applications can use this approach to gain performance improvements.

Manually compiled queries

In previous versions of EF and Linq to SQL, there was an API for manually or explicitly compiling queries, which allowed applications to cache translated queries so that they Can be compiled once and executed multiple times.

Although EF Core can automatically compile and cache queries based on query expressions, this mechanism can obtain a small query performance improvement by bypassing hash calculations or caching, allowing applications to use delegates that have already been called. Query passed by chain compilation.

private static Func<CustomerContext, int, Customer> _customerById =
    EF.CompileQuery((CustomerContext db, int id) =>
        db.Customers
            .Include(c => c.Address)
            .Single(c => c.Id == id));

...using (var db = new CustomerContext())
{   var customer = _customerById(db, 147);
}

Others

EF Core 2.0 will also make some major adjustments to some logging and diagnostic infrastructure, as well as integration with Azure Application Insights.

The addition of Lazy Loading (lazy loading) function is still under discussion, and this function may be added in EF Core 2.1.

The above is the detailed content of EF Core 2.0 new features. For more information, please follow other related articles on the PHP Chinese website!