旧 ADO.NET 查询的 LINQ 查询

Question

我不习惯使用 LINQ 编写 JOIN 语句。我正在尝试将这个旧查询转换为 LINQ Lambda 语法，并努力了解如何进行它。任何帮助将不胜感激。

SELECT p.id, p.code, u.email, b.date
FROM 
Patients p
LEFT JOIN Users u
ON u.patientid =p.id and u.id=p.primarycontactid
INNER JOIN BillingSettings b ON b.PracticeId = p.id and b.isDue=1
WHERE p.status=1
AND p.appointmentdate > now() and p.appointmentdate < now() + 90
and b.expirationdate < now()
order by p.id

Answer 1

我在没有编译器的情况下写了这篇文章，所以它可能是错误的，但通常你的答案如下。

var now = DateTime.Now();

var query = 
    from p in db.Patients 
    join u in db.Users on new { patientid = p.id, p.primarycontactid} equals { u.patientid, primarycontactid = u.id}
    from u in userPatient.DefaultIfEmpty()
    join b in db.BillingSettings on b.PracticeId equals p.id
    where p.status == 1 &&
        p.appointmentdate > now && p.appointmentdate < now.AddDays(90) &&
        (b == null || (b.isDue == 1 && b.expirationdate < now))
    orderby p.id
    select new
    {
        p.id,
        p.code,
        email = u?.email
        date = b?.date 
    };