c# - 如何在 EF 中指定左连接？

Question

我的模型:

public partial class history_builds
{
    public int ID { get; set; }
    public int build { get; set; }
    public int br { get; set; }
    public int tag { get; set; }
    public string line { get; set; }
    public int rev { get; set; }
    public int user_ID { get; set; }
    public string distrib_path { get; set; }
    public string setup_path { get; set; }
    public System.DateTime build_date { get; set; }
    public string product { get; set; }
}

public partial class history_uploads
{
    public int ID { get; set; }
    public int ID_user { get; set; }
    public string Line { get; set; }
    public int Build { get; set; }
    public string Distrib { get; set; }
    public System.DateTime Time_upload { get; set; }
    public int Status { get; set; }
}

public partial class user
{
    public int ID { get; set; }
    public string Name { get; set; }
    public int ID_group { get; set; }
}

上下文:

public DbSet<history_builds> history_builds { get; set; }
public DbSet<history_uploads> history_uploads { get; set; }
public DbSet<user> users { get; set; }

我尝试像这样进行左连接 Entity framework left join

var items = entities.history_builds
    .Join(
        entities.users.DefaultIfEmpty(),
        hb => hb.user_ID,
        u => u.ID,
        (hb, u) =>
            new {
                hb.distrib_path,
                hb.setup_path,
                hb.build_date,
                hb.build,
                User = (u == null ? String.Empty : u.Name),
                hb.rev
            }
    )
    .Join(entities.history_uploads.DefaultIfEmpty(),
        hb => hb.build,
        hu => hu.Build,
        (hb, hu) =>
            new HistoryBuidItem {
                Revision = hb.rev,
                Build = hb.build,
                DistribPath = hb.distrib_path,
                SetupPath = hb.setup_path,
                BuildDate = hb.build_date,
                User = hb.User,
                IsUpload = (hu == null ? true : false)
            }
    )
    .Where(x => ids.Contains(x.Revision))
    .ToList();

但它不起作用，EF 仍然发出内部连接 ​​sql 代码，有什么问题吗？

Answer 1

你应该使用 GroupJoin为此。

看例子:

var customers = db.Customer
                  .GroupJoin(db.SpecialCustomer, c => c.ID, g => g.CustomerId, (f, b) => new { f, b })
                  .SelectMany(z => z.b.DefaultIfEmpty(), (z, g) => new { z, g });