ADO.Net Entity Framework Linq To Entities 语法功能汇编
Linq To Entities 的語法基礎可以參考:
Microsoft Language Integrated Query (LINQ) 從入門到精通
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1.使用ObjectQuery類的ToTraceString()方法顯示查詢SQL語句
???????????? Console.WriteLine(customers.ToTraceString());
2.基于表達式的查詢語法
??? ObjectQuery<Customers> customers = edm.Customers;
??? IQueryable<Customers> cust1 = from c in customers
????????????????????????????????? where c.CustomerID == "ALFKI"
????????????????????????????????? select c;
3.基于方法的查詢語法
??? var cust2 = edm.Customers.Where(c => c.CustomerID == "ALFKI");
4.排序分頁
IQueryable<Customers> cust10 = (from c in customers
??????????????????????????????????????? orderby c.CustomerID
??????????????????????????????????????? select c).Skip(0).Take(10);
或者
var cust = edm.Customers.OrderBy(c => c.CustomerID).Skip(0).Take(10);
5.可使用的聚合運算符有Average、Count、Max、Min 和 Sum。
????? var maxuprice = edm.Products.Max(p => p.UnitPrice);
????? Console.WriteLine(maxuprice.Value);
6. 可以的連接有Join 和 GroupJoin 方法。GroupJoin組聯(lián)接等效于左外部聯(lián)接,它返回第一個(左側)數(shù)據(jù)源的每個元素(即使其他數(shù)據(jù)源中沒有關聯(lián)元素)。
using (var edm = new NorthwindEntities())
??? {
????? var query = from d in edm.Order_Details
????????????????? join order in edm.Orders
????????????????? on d.OrderID equals order.OrderID
????????????????? select new
??????????????????? {
??????????????????????? OrderId = order.OrderID,
??????????????????????? ProductId = d.ProductID,
??????????????????????? UnitPrice = d.UnitPrice
??????????????????? };
??????? foreach (var q in query)
??????? Console.WriteLine("{0},{1},{2}",q.OrderId,q.ProductId,q.UnitPrice);
}
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參考文章:
http://www.pin5i.com/showtopic-24045.html
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未完成!
轉載于:https://www.cnblogs.com/doubleyan/archive/2010/03/07/2164770.html
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