[英]Entity Framework Linq, Left Join and group with SUM and Count
在將SQL轉換為Linq時,我需要一些幫助。 在MySQL中非常簡單...
Table: customers
ID Name
1 Bill
2 John
Table: purchases
ID CustomerID CompletedTransaction
1 1 False
2 2 True
3 1 True
4 1 True
SELECT c.ID
c.Name,
COUNT(p.ID) AS TotalPurchases,
SUM(CASE WHEN p.CompletedTransaction = TRUE THEN 1 ELSE 0 END) AS TotalCompleted
FROM customers c
LEFT JOIN purchases p ON c.ID = p.CustomerID
GROUP BY c.ID
Expected Result:
1, Bill, 3, 2
2, John, 1, 1
我已經看到了一些有關如何在Linq中實現左聯接的示例,但是我不確定如何在其中包括SUM和Count。 我在Linq中看到過一些示例,其中從組鍵中選擇了返回的字段。 這是否意味着,如果我在customers表中有更多字段想要返回,例如地址和其他聯系方式,則必須將它們包括在聯接中才能選擇它們? 希望這是有道理的。 感謝任何可能幫助我指出正確方向的幫助或鏈接。
謝謝
這是樣本
class Program
{
static void Main(string[] args)
{
List<Customers> customers = new List<Customers>();
customers.Add(new Customers() { ID = 1, Name = "Bill" });
customers.Add(new Customers() { ID = 2, Name = "John" });
List<Purchases> purchases = new List<Purchases>();
purchases.Add(new Purchases() { ID = 1, CustomerID = 1, CompletedTransaction = false });
purchases.Add(new Purchases() { ID = 2, CustomerID = 2, CompletedTransaction = true });
purchases.Add(new Purchases() { ID = 3, CustomerID = 1, CompletedTransaction = true });
purchases.Add(new Purchases() { ID = 4, CustomerID = 1, CompletedTransaction = true });
IEnumerable<JoinResult> results = from c in customers
join p in purchases
on c.ID equals p.CustomerID
group new { c, p } by new {p.CustomerID, c.Name} into r
select new JoinResult
{
CustomerID = r.Key.CustomerID,
CustomerName = r.Key.Name,
TotalPurchases = r.Count(),
TotalCompleteTransaction = r.Where(s=> s.p.CompletedTransaction).Count()
};
foreach(JoinResult r in results)
{
Console.WriteLine($"CustomerID : {r.CustomerID} | Name : {r.CustomerName} | TotalPurchases : {r.TotalPurchases} | TotalCompleteTransaction : {r.TotalCompleteTransaction}");
}
Console.ReadKey();
}
}
class Customers
{
public int ID { get; set; }
public string Name { get; set; }
}
class Purchases
{
public int ID { get; set; }
public int CustomerID { get; set; }
public bool CompletedTransaction { get; set; }
}
class JoinResult
{
public int CustomerID { get; set; }
public string CustomerName { get; set; }
public int TotalPurchases { get; set; }
public int TotalCompleteTransaction { get; set; }
}
var answer = (from c in db.customers
join p in db.purchases
on c.ID = p.CustomerID into subs
from sub in subs.DefaultIfEmpty()
group sub by new { c.ID, c.Name } into gr
select new {
gr.Key.ID,
gr.Key.Name,
Total = gr.Count(x => x != null),
CountCompleted = gr.Count(x => x != null && x.CompletedTransaction)
}).ToList();
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