c# - LINQ 使用 Take(1) 连接(左外)

Question

如果没有任何地址(内部连接)，我有以下 LINQ 返回零。我如何将其设为 Outer Join 然后仅 Take(1)？

var results = query.Join(
                DB.tblAddresses.Where(t => t.AddressTypeID == 'm' || t.AddressTypeID == 'b').OrderByDescending(x => x.AddressTypeID),
                p => p.PersonID,
                a => a.PersonID,
                (p, a) =>
                new
                    {
                        p.PersonID,
                        p.LastName,
                        p.FirstName,
                        p.MiddleName,
                        p.SSN,
                        p.BirthDate,
                        p.DeathDate,
                        AddressLine1 = a.AddressLine1 ?? string.Empty
                });

            return results.CopyLinqToDataTable();

Answer 1

使用GroupJoin :

var results = query.GroupJoin(
    addresses,
    p => p.PersonID,
    a => a.PersonID,
    (p, a) =>
    new
    {
        p.PersonID,
        p.LastName,
        p.FirstName,
        p.MiddleName,
        p.SSN,
        p.BirthDate,
        p.DeathDate,
        AddressLine1 = a.Any()
            ? (a.First().AddressLine1 ?? string.Empty)
            : null
    });