如何使用EF Core 2.1.0和代理进行延迟加载

Question

我有以下型号:

public class Session
{
    public int SessionID { get; set; }
    public int UserID { get; set; }

    public virtual User User { get; set; }
}

public class User
{
    public int UserID { get; set; }
    public int OrganizationID { get; set; }

    public virtual ICollection<Session> Sessions { get; set; }
    public virtual Organization Organization { get; set; }
}

public class Organization
{
    public int OrganizationID { get; set; }

    public virtual ICollection<User> Users { get; set; }
}

注册DbContext为:

modelBuilder.Entity<Session>(entity =>
{
    entity.ToTable("sessions");

    entity.Property(e => e.SessionID).HasColumnName("id");
    entity.Property(e => e.UserID).HasColumnName("user_id");

    entity.HasOne(e => e.User)
        .WithMany(e => e.Sessions)
        .HasForeignKey(e => e.UserID);
}

modelBuilder.Entity<User>(entity =>
{
    entity.ToTable("users");

    entity.Property(e => e.UserID).HasColumnName("id");
    entity.Property(e => e.OrganizationID).HasColumnName("organization_id");

    entity.HasOne(e => e.Organization)
        .WithMany(e => e.Users)
        .HasForeignKey(e => e.OrganizationID);
}

modelBuilder.Entity<Organization>(entity =>
{
    entity.ToTable("organizations");

    entity.Property(e => e.OrganizationID).HasColumnName("id");
}

我试图使用延迟加载与Microsoft.EntityFrameworkCore.Proxies所描述的在这里:

builder.Register(c =>
{
    var optionsBuilder = new DbContextOptionsBuilder<Context>();
    optionsBuilder
        .UseLazyLoadingProxies()
        /* more options */
        ;

    var opts = optionsBuilder.Options;

    return new Context(opts);
}).As<DbContext>().InstancePerLifetimeScope();

我正在使用查询会话context.All<Session>.然而,Session.User和Session.User.Organization默认情况下为空.要加载它们,我必须做类似的事情context.All<Session>().Include(s => s.User).Include(s => s.User.Organization).我怎么能避免这种情况？为什么不起作用UseLazyLoadingProxies？

---

• .NET核心版本: 2.1.300-preview2-008533
• 目标: netcoreapp2.1
• EF Core(和Proxies)版本: 2.1.0-preview2-final

Answer 1

在Asp.net Core 2.1中使用代理配置延迟加载的步骤

1. 安装Microsoft.EntityFrameworkCore.Proxies包

2. 启用LazyLoadingProxies您可以通过调用UseLazyLoadingProxies来启用它:

   protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)=> optionsBuilder .UseLazyLoadingProxies().UseSqlServer(myConnectionString);

或者在使用AddDbContext时:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    => optionsBuilder
        .UseLazyLoadingProxies()
        .UseSqlServer(myConnectionString);

3. 然后,EF Core将为可以覆盖的任何导航属性启用延迟加载 - 也就是说,它必须是虚拟的.

Answer 2

您可以尝试在Startup.cslike中配置代理

public void ConfigureServices(IServiceCollection services)
{
    #region Database configuration

    // Database configuration
    services.AddDbContext<DbContext>(options =>
        options.UseLazyLoadingProxies()
            .UseSqlServer(Configuration.GetConnectionString("MyConnectionString")));

    #endregion Database configuration
}

顺便说一句,您已经可以将应用程序包更新为纯2.1.0(非最终版或RC版).配置可能不起作用的原因之一是组件的不稳定版本.

NB:Microsoft.EntityFrameworkCore.Proxies.dll从nuget独立于EFCore安装