如何使用 EF Core 2.1.0 和代理进行延迟加载 [英] How to make lazy-loading work with EF Core 2.1.0 and proxies

问题描述

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; }
}

在 DbContext 中注册为:

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");
}

我正在尝试对 Microsoft.EntityFrameworkCore.Proxies 使用延迟加载，如此处:

I'm trying to use lazy loading with Microsoft.EntityFrameworkCore.Proxies as described here:

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 context.All 查询会话.但是，Session.User 和 Session.User.Organization 默认为空.要加载它们，我必须执行诸如 context.All().Include(s => s.User).Include(s => s.User.Organization) 之类的操作.我怎样才能避免这种情况?为什么 UseLazyLoadingProxies 不起作用?

I'm querying sessions using context.All<Session>. However, Session.User and Session.User.Organization are null by default. To load them I have to do something like context.All<Session>().Include(s => s.User).Include(s => s.User.Organization). How can I avoid that? Why doesn't UseLazyLoadingProxies work?

• .NET Core 版本:2.1.300-preview2-008533
• 目标:netcoreapp2.1
• EF Core(和代理)版本:2.1.0-preview2-final

推荐答案

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. 启用延迟加载代理您可以通过调用 UseLazyLoadingProxies 来启用它:

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

或者在使用 AddDbContext 时:

Or when using AddDbContext:

.AddDbContext<BloggingContext>(
b => b.UseLazyLoadingProxies()
      .UseSqlServer(myConnectionString));

1. EF Core 将为任何可以覆盖的导航属性启用延迟加载 - 也就是说，它必须是虚拟的.

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