從本節(jié)開始,本文正式更名為C#3.0入門系列。先發(fā)布一則消息,VS2007 Beta版本已經(jīng)發(fā)布咯,下載地址:
http://www.microsoft.com/downloads/details.aspx?FamilyID=1FF0B35D-0C4A-40B4-915A-5331E11C39E6&displaylang=en
大家快去下載呀,我也好和大家一起體驗該版本最新功能呀。
dlinq也更名為linq to sql.本文也跟著做相應(yīng)變化,稍候,我會去更新前面的文章。我們先接著講linq的語法。
Select操作
最簡單的
name type形式的:
shaped形式的:
nested形式的:
Distinct形式的:
select distinct city from customers
where操作:
最簡單的
1
,????????????var?q?
=
????????????????from?c?
in
?db.Customers
????????????????where?c.City?
==
?
"
London
"
????????????????select?c;
2
,????????????var?q?
=
????????????????from?e?
in
?db.Employees
????????????????where?e.HireDate?
>=
?
new
?DateTime(
1994
,?
1
,?
1
)
????????????????select?e;
或與關(guān)系的where條件
欠套在first操作中的where條件:
first操作,其實質(zhì)就是在sql語句前,加了一個top 1.
http://www.microsoft.com/downloads/details.aspx?FamilyID=1FF0B35D-0C4A-40B4-915A-5331E11C39E6&displaylang=en
大家快去下載呀,我也好和大家一起體驗該版本最新功能呀。
dlinq也更名為linq to sql.本文也跟著做相應(yīng)變化,稍候,我會去更新前面的文章。我們先接著講linq的語法。
Select操作
最簡單的
1
,????????????var?q?
=
????????????????from?c? in ?db.Customers
????????????????select?c.ContactName;
匿名類的
????????????????from?c? in ?db.Customers
????????????????select?c.ContactName;
1
,????????????var?q?
=
????????????????from?c? in ?db.Customers
????????????????select? new ?{c.ContactName,?c.Phone};
2 ,????????????var?q? =
????????????????from?e? in ?db.Employees
????????????????select? new ?{Name? = ?e.FirstName? + ? " ? " ? + ?e.LastName,?Phone? = ?e.HomePhone};
3 ,????????????var?q? =
????????????????from?p? in ?db.Products
????????????????select? new ?{p.ProductID,?HalfPrice? = ?p.UnitPrice? / ? 2 };
條件的
????????????????from?c? in ?db.Customers
????????????????select? new ?{c.ContactName,?c.Phone};
2 ,????????????var?q? =
????????????????from?e? in ?db.Employees
????????????????select? new ?{Name? = ?e.FirstName? + ? " ? " ? + ?e.LastName,?Phone? = ?e.HomePhone};
3 ,????????????var?q? =
????????????????from?p? in ?db.Products
????????????????select? new ?{p.ProductID,?HalfPrice? = ?p.UnitPrice? / ? 2 };
????????????var?q?
=
????????????????from?p? in ?db.Products
????????????????select? new ?{p.ProductName,?Availability? = ?p.UnitsInStock? - ?p.UnitsOnOrder? < ? 0 ? ? ? " Out?Of?Stock " :? " In?Stock " };
這種條件的會被翻譯成sql中{case when condition then else}的。
????????????????from?p? in ?db.Products
????????????????select? new ?{p.ProductName,?Availability? = ?p.UnitsInStock? - ?p.UnitsOnOrder? < ? 0 ? ? ? " Out?Of?Stock " :? " In?Stock " };
name type形式的:
????????????var?q?
=
????????????????from?e? in ?db.Employees????????????????
????????????????select? new ?Name?{FirstName? = ?e.FirstName,?LastName? = ?e.LastName};
只所以是name type的,是因為Name類是已經(jīng)定義好的,也就是說,你可以用這種方式,返回你需要類型的對象集.
????????????????from?e? in ?db.Employees????????????????
????????????????select? new ?Name?{FirstName? = ?e.FirstName,?LastName? = ?e.LastName};
shaped形式的:
????????????var?q?
=
????????????????from?c? in ?db.Customers
????????????????select? new ?{
????????????????????c.CustomerID,
????????????????????CompanyInfo? = ? new ?{c.CompanyName,?c.City,?c.Country},
????????????????????ContactInfo? = ? new ?{c.ContactName,?c.ContactTitle}
????????????????};
該形式,其select操作使用了匿名對象,而這個匿名對象中,其屬性也是個匿名對象。
????????????????from?c? in ?db.Customers
????????????????select? new ?{
????????????????????c.CustomerID,
????????????????????CompanyInfo? = ? new ?{c.CompanyName,?c.City,?c.Country},
????????????????????ContactInfo? = ? new ?{c.ContactName,?c.ContactTitle}
????????????????};
nested形式的:
????????????var?q?
=
????????????????from?o? in ?db.Orders
????????????????select? new ?{
????????????????????o.OrderID,
????????????????????DiscountedProducts? =
????????????????????????from?od? in ?o.OrderDetails
????????????????????????where?od.Discount? > ? 0.0
????????????????????????select?od,
????????????????????FreeShippingDiscount? = ?o.Freight
????????????????};
其返回的對象集中的每個對象DiscountedProducts屬性中,又包含一個小的集合。也就是每個對象也是一個集合類。
????????????????from?o? in ?db.Orders
????????????????select? new ?{
????????????????????o.OrderID,
????????????????????DiscountedProducts? =
????????????????????????from?od? in ?o.OrderDetails
????????????????????????where?od.Discount? > ? 0.0
????????????????????????select?od,
????????????????????FreeShippingDiscount? = ?o.Freight
????????????????};
Distinct形式的:
????????????var?q?
=
?(
????????????????from?c? in ?db.Customers
????????????????select?c.City?)
????????????????.Distinct();
該形式,篩選該字段中不相同的值。會被翻譯為
????????????????from?c? in ?db.Customers
????????????????select?c.City?)
????????????????.Distinct();
select distinct city from customers
where操作:
最簡單的









1
,????????????var?q?
=
????????????????from?p? in ?db.Products
????????????????where?p.UnitsInStock? <= ?p.ReorderLevel? && ? ! p.Discontinued
????????????????select?p;
2 ,????????????var?q? =
????????????????from?p? in ?db.Products
????????????????where?p.UnitPrice? > ?10m? || ?p.Discontinued
????????????????select?p;
3 ,????????????var?q? =
????????????????db.Products.Where(p => p.UnitPrice? > ?10m).Where(p => p.Discontinued);
在上例中,1和2語句先被翻譯成類似3語句的形式,再被翻譯成sql語句,送回數(shù)據(jù)服務(wù)器。他們基本上一樣的。
????????????????from?p? in ?db.Products
????????????????where?p.UnitsInStock? <= ?p.ReorderLevel? && ? ! p.Discontinued
????????????????select?p;
2 ,????????????var?q? =
????????????????from?p? in ?db.Products
????????????????where?p.UnitPrice? > ?10m? || ?p.Discontinued
????????????????select?p;
3 ,????????????var?q? =
????????????????db.Products.Where(p => p.UnitPrice? > ?10m).Where(p => p.Discontinued);
欠套在first操作中的where條件:
first操作,其實質(zhì)就是在sql語句前,加了一個top 1.
1
,????????????Customer?cust?
=
?db.Customers.First(c?
=>
?c.CustomerID?
==
?
"
BONAP
"
);
2 ????????????Order?ord? = ?db.Orders.First(o? => ?o.Freight? > ? 10.00M );
第一個例子,是篩選customerid為"BONAP"的客戶,第二個篩選訂單運費大于10的訂單。First操作必須用這種級連的形式。比如
2 ????????????Order?ord? = ?db.Orders.First(o? => ?o.Freight? > ? 10.00M );
Shipper?shipper?
=
?db.Shippers.First();
也可以把linq的expression和級連的形式混合使用,比如第一個例子,加入first操作,
????????????var?q?
=
????????????????(from?c? in ?db.Customers
????????????????where?c.City? == ? " London "
????????????????select?c).First();
如果加入first操作,其返回是一個具體的對象,而不是一個集合。如果first操作沒有條件,它只是簡單的在sql語句中添加top 1,如果有條件,它在翻譯時,就會加入條件語句。
????????????????(from?c? in ?db.Customers
????????????????where?c.City? == ? " London "
????????????????select?c).First();
?
?
TrackBack: http://www.cnblogs.com/126/archive/2007/01/28/632454.html
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