LINQ学习笔记(二)--感受篇二
2007-09-27 00:32
369 查看
通过前面MikeTaulty的讲解,我对LINQ的使用有个大概的感观认识,下面再来看看Scottgu在asp.net中的例子.(其实LINQ只和后台有关,很表现层没有关系的)
Demo1:
1. 同样地我们在创建网站后,添加一个dbml文件NorthwindDemo1.dbml(dbml是Database Markup Language,是一个标准的XML文件,其实可以把他看作是一个生成映射的中间文件,因为我们生成的实体类时候,有的是VB,是C#,或者其他的)
用VS自带的可视化的O/R Mapping工具,可以通过简单的拖拉,生成dbml.,demo1的结构如下:
dbml文件源码如下:
<?xml version="1.0" encoding="utf-16"?>
<Database Name="E:VS2008LINQ学习TESTCODELINQTEST2_WEB_SCOTTGUAPP_DATANORTHWND.MDF" Class="NorthwindDataContext" xmlns="http://schemas.microsoft.com/linqtosql/dbml/2007">
<Connection Mode="WebSettings" ConnectionString="Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|NORTHWND.MDF;Integrated Security=True;Connect Timeout=30;User Instance=True" SettingsObjectName="System.Configuration.ConfigurationManager.ConnectionStrings" SettingsPropertyName="NORTHWNDConnectionString" Provider="System.Data.SqlClient" />
<Table Name="dbo.Categories" Member="Categories">
<Type Name="Categories">
<Column Name="CategoryID" Type="System.Int32" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" CanBeNull="false" />
<Column Name="CategoryName" Type="System.String" DbType="NVarChar(15) NOT NULL" CanBeNull="false" />
<Column Name="Description" Type="System.String" DbType="NText" CanBeNull="true" UpdateCheck="Never" />
<Column Name="Picture" Type="System.Byte[]" DbType="Image" CanBeNull="true" UpdateCheck="Never" />
<Association Name="Categories_Products" Member="Products" OtherKey="CategoryID" Type="Products" />
</Type>
</Table>
<Table Name="dbo.Products" Member="Products">
<Type Name="Products">
<Column Name="ProductID" Type="System.Int32" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" CanBeNull="false" />
<Column Name="ProductName" Type="System.String" DbType="NVarChar(40) NOT NULL" CanBeNull="false" />
<Column Name="SupplierID" Type="System.Int32" DbType="Int" CanBeNull="true" />
<Column Name="CategoryID" Type="System.Int32" DbType="Int" CanBeNull="true" />
<Column Name="QuantityPerUnit" Type="System.String" DbType="NVarChar(20)" CanBeNull="true" />
<Column Name="UnitPrice" Type="System.Decimal" DbType="Money" CanBeNull="true" />
<Column Name="UnitsInStock" Type="System.Int16" DbType="SmallInt" CanBeNull="true" />
<Column Name="UnitsOnOrder" Type="System.Int16" DbType="SmallInt" CanBeNull="true" />
<Column Name="ReorderLevel" Type="System.Int16" DbType="SmallInt" CanBeNull="true" />
<Column Name="Discontinued" Type="System.Boolean" DbType="Bit NOT NULL" CanBeNull="false" />
<Association Name="Categories_Products" Member="Categories" ThisKey="CategoryID" Type="Categories" IsForeignKey="true" />
</Type>
</Table>
</Database>
我们可以看到,里面的内容也很好理解,主要标记了要生成的表和字段的一些属性和关系,现在主要是感受使用,就先不考究他了.
2. 我们在页面中添加一个GridView做数据输出,后台我们只是做一个简单的select,然后绑定输出,在Page_Load中添加如下代码:
NorthwindDataContext NwCtx = new NorthwindDataContext();
var query = from p in NwCtx.Products
select p;
//在这里我们可以看出,其实这个query返回的是一个数据集,可以作为数据源绑定输出
GridViewDemo1.DataSource = query;
GridViewDemo1.DataBind();
结果输出:
后台执行的SQL同样简单:
SELECT [t0].[ProductID], [t0].[ProductName], [t0].[SupplierID], [t0].[CategoryID], [t0].[QuantityPerUnit], [t0].[UnitPrice], [t0].[UnitsInStock], [t0].[UnitsOnOrder], [t0].[ReorderLevel], [t0].[Discontinued]
FROM [dbo].[Products] AS [t0]
当然我可以加上查询的条件:
如:
var query = from p in NwCtx.Products
where p.Categories.CategoryName.StartsWith("C")
select p;
又如:
var query = from p in NwCtx.Products
where p.Categories.Products.Count > 5
select p;
当然我们还可以重编输出的内容和加上一些运算输出,如:
var query = from p in NwCtx.Products
where p.Categories.Products.Count > 5
select new
...{
p.ProductID,
p.ProductName
};
又如:
var query = from p in NwCtx.Products
where p.Categories.Products.Count > 5
select new
...{
产品ID = p.ProductID,
产品名字 = p.ProductName,
总数 = p.Order_Details.Sum(o => o.Quantity),
总收入 = p.Order_Details.Sum(o => o.Quantity * o.UnitPrice)
};
query运行的SQL:
SELECT [t0].[ProductID], [t0].[ProductName], (
SELECT SUM(CONVERT(Int,[t3].[Quantity]))
FROM [dbo].[Order Details] AS [t3]
WHERE [t3].[ProductID] = [t0].[ProductID]
) AS [value], (
SELECT SUM((CONVERT(Decimal(29,4),[t4].[Quantity])) * [t4].[UnitPrice])
FROM [dbo].[Order Details] AS [t4]
WHERE [t4].[ProductID] = [t0].[ProductID]
) AS [value2]
FROM [dbo].[Products] AS [t0]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Categories] AS [t1], [dbo].[Products] AS [t2]
WHERE ([t1].[CategoryID] = [t0].[CategoryID]) AND ([t2].[CategoryID] = [t1].[CategoryID])
)) > 5
注意,此时要在dbml里面加入两张表,不然会出错哦:
写着这些语句,刚开始我有些奇怪,为什么不直接按着T-SQL的习惯,把Select语句写到前面呢?查了一下资料,据说是MS为了IDE的智能感应而作出的变化,因为当我们没有写from语句前,是很难知道要select的到底是什么类型,那么就很难能做到代码提醒了,呵呵.
刚才说到query返回的是一个数据集,那么我们就可以对他进行进一步的抽取数据,例如我们可以利用LINQ提供的匿名类对它进行一些操作:
如支取前面十条数据:
GridViewDemo1.DataSource = query.Take(10);
结果:
又如取11到20的数据:
只要简单的加上Skip就可以了,当中有个原则,每次返回都是一个数据集,而再下一层操作都是在上一层数据集里面再抽取一个数据集.
GridViewDemo1.DataSource = query.Skip(10).Take(10);
结果:
看看使用SQL的变化,就更容易理解这一点:
单纯的query:
SELECT [t0].[ProductID], [t0].[ProductName], (
SELECT SUM(CONVERT(Int,[t3].[Quantity]))
FROM [dbo].[Order Details] AS [t3]
WHERE [t3].[ProductID] = [t0].[ProductID]
) AS [value], (
SELECT SUM((CONVERT(Decimal(29,4),[t4].[Quantity])) * [t4].[UnitPrice])
FROM [dbo].[Order Details] AS [t4]
WHERE [t4].[ProductID] = [t0].[ProductID]
) AS [value2]
FROM [dbo].[Products] AS [t0]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Categories] AS [t1], [dbo].[Products] AS [t2]
WHERE ([t1].[CategoryID] = [t0].[CategoryID]) AND ([t2].[CategoryID] = [t1].[CategoryID])
)) > 5
加上skip和take:
SELECT TOP 10 [t6].[产品ID], [t6].[产品名字], [t6].[总数], [t6].[总收入]
FROM (
SELECT ROW_NUMBER() OVER (ORDER BY [t3].[ProductID], [t3].[ProductName], [t3].[value], [t3].[value2]) AS [ROW_NUMBER], [t3].[ProductID] AS [产品ID], [t3].[ProductName] AS [产品名字], [t3].[value] AS [总数], [t3].[value2] AS [总收入]
FROM (
SELECT [t0].[ProductID], [t0].[ProductName], (
SELECT SUM(CONVERT(Int,[t1].[Quantity]))
FROM [dbo].[Order Details] AS [t1]
WHERE [t1].[ProductID] = [t0].[ProductID]
) AS [value], (
SELECT SUM((CONVERT(Decimal(29,4),[t2].[Quantity])) * [t2].[UnitPrice])
FROM [dbo].[Order Details] AS [t2]
WHERE [t2].[ProductID] = [t0].[ProductID]
) AS [value2], [t0].[CategoryID]
FROM [dbo].[Products] AS [t0]
) AS [t3]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Categories] AS [t4], [dbo].[Products] AS [t5]
WHERE ([t4].[CategoryID] = [t3].[CategoryID]) AND ([t5].[CategoryID] = [t4].[CategoryID])
)) > 5
) AS [t6]
WHERE [t6].[ROW_NUMBER] > 10
Demo1:
1. 同样地我们在创建网站后,添加一个dbml文件NorthwindDemo1.dbml(dbml是Database Markup Language,是一个标准的XML文件,其实可以把他看作是一个生成映射的中间文件,因为我们生成的实体类时候,有的是VB,是C#,或者其他的)
用VS自带的可视化的O/R Mapping工具,可以通过简单的拖拉,生成dbml.,demo1的结构如下:
dbml文件源码如下:
<?xml version="1.0" encoding="utf-16"?>
<Database Name="E:VS2008LINQ学习TESTCODELINQTEST2_WEB_SCOTTGUAPP_DATANORTHWND.MDF" Class="NorthwindDataContext" xmlns="http://schemas.microsoft.com/linqtosql/dbml/2007">
<Connection Mode="WebSettings" ConnectionString="Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|NORTHWND.MDF;Integrated Security=True;Connect Timeout=30;User Instance=True" SettingsObjectName="System.Configuration.ConfigurationManager.ConnectionStrings" SettingsPropertyName="NORTHWNDConnectionString" Provider="System.Data.SqlClient" />
<Table Name="dbo.Categories" Member="Categories">
<Type Name="Categories">
<Column Name="CategoryID" Type="System.Int32" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" CanBeNull="false" />
<Column Name="CategoryName" Type="System.String" DbType="NVarChar(15) NOT NULL" CanBeNull="false" />
<Column Name="Description" Type="System.String" DbType="NText" CanBeNull="true" UpdateCheck="Never" />
<Column Name="Picture" Type="System.Byte[]" DbType="Image" CanBeNull="true" UpdateCheck="Never" />
<Association Name="Categories_Products" Member="Products" OtherKey="CategoryID" Type="Products" />
</Type>
</Table>
<Table Name="dbo.Products" Member="Products">
<Type Name="Products">
<Column Name="ProductID" Type="System.Int32" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" CanBeNull="false" />
<Column Name="ProductName" Type="System.String" DbType="NVarChar(40) NOT NULL" CanBeNull="false" />
<Column Name="SupplierID" Type="System.Int32" DbType="Int" CanBeNull="true" />
<Column Name="CategoryID" Type="System.Int32" DbType="Int" CanBeNull="true" />
<Column Name="QuantityPerUnit" Type="System.String" DbType="NVarChar(20)" CanBeNull="true" />
<Column Name="UnitPrice" Type="System.Decimal" DbType="Money" CanBeNull="true" />
<Column Name="UnitsInStock" Type="System.Int16" DbType="SmallInt" CanBeNull="true" />
<Column Name="UnitsOnOrder" Type="System.Int16" DbType="SmallInt" CanBeNull="true" />
<Column Name="ReorderLevel" Type="System.Int16" DbType="SmallInt" CanBeNull="true" />
<Column Name="Discontinued" Type="System.Boolean" DbType="Bit NOT NULL" CanBeNull="false" />
<Association Name="Categories_Products" Member="Categories" ThisKey="CategoryID" Type="Categories" IsForeignKey="true" />
</Type>
</Table>
</Database>
我们可以看到,里面的内容也很好理解,主要标记了要生成的表和字段的一些属性和关系,现在主要是感受使用,就先不考究他了.
2. 我们在页面中添加一个GridView做数据输出,后台我们只是做一个简单的select,然后绑定输出,在Page_Load中添加如下代码:
NorthwindDataContext NwCtx = new NorthwindDataContext();
var query = from p in NwCtx.Products
select p;
//在这里我们可以看出,其实这个query返回的是一个数据集,可以作为数据源绑定输出
GridViewDemo1.DataSource = query;
GridViewDemo1.DataBind();
结果输出:
后台执行的SQL同样简单:
SELECT [t0].[ProductID], [t0].[ProductName], [t0].[SupplierID], [t0].[CategoryID], [t0].[QuantityPerUnit], [t0].[UnitPrice], [t0].[UnitsInStock], [t0].[UnitsOnOrder], [t0].[ReorderLevel], [t0].[Discontinued]
FROM [dbo].[Products] AS [t0]
当然我可以加上查询的条件:
如:
var query = from p in NwCtx.Products
where p.Categories.CategoryName.StartsWith("C")
select p;
又如:
var query = from p in NwCtx.Products
where p.Categories.Products.Count > 5
select p;
当然我们还可以重编输出的内容和加上一些运算输出,如:
var query = from p in NwCtx.Products
where p.Categories.Products.Count > 5
select new
...{
p.ProductID,
p.ProductName
};
又如:
var query = from p in NwCtx.Products
where p.Categories.Products.Count > 5
select new
...{
产品ID = p.ProductID,
产品名字 = p.ProductName,
总数 = p.Order_Details.Sum(o => o.Quantity),
总收入 = p.Order_Details.Sum(o => o.Quantity * o.UnitPrice)
};
query运行的SQL:
SELECT [t0].[ProductID], [t0].[ProductName], (
SELECT SUM(CONVERT(Int,[t3].[Quantity]))
FROM [dbo].[Order Details] AS [t3]
WHERE [t3].[ProductID] = [t0].[ProductID]
) AS [value], (
SELECT SUM((CONVERT(Decimal(29,4),[t4].[Quantity])) * [t4].[UnitPrice])
FROM [dbo].[Order Details] AS [t4]
WHERE [t4].[ProductID] = [t0].[ProductID]
) AS [value2]
FROM [dbo].[Products] AS [t0]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Categories] AS [t1], [dbo].[Products] AS [t2]
WHERE ([t1].[CategoryID] = [t0].[CategoryID]) AND ([t2].[CategoryID] = [t1].[CategoryID])
)) > 5
注意,此时要在dbml里面加入两张表,不然会出错哦:
写着这些语句,刚开始我有些奇怪,为什么不直接按着T-SQL的习惯,把Select语句写到前面呢?查了一下资料,据说是MS为了IDE的智能感应而作出的变化,因为当我们没有写from语句前,是很难知道要select的到底是什么类型,那么就很难能做到代码提醒了,呵呵.
刚才说到query返回的是一个数据集,那么我们就可以对他进行进一步的抽取数据,例如我们可以利用LINQ提供的匿名类对它进行一些操作:
如支取前面十条数据:
GridViewDemo1.DataSource = query.Take(10);
结果:
又如取11到20的数据:
只要简单的加上Skip就可以了,当中有个原则,每次返回都是一个数据集,而再下一层操作都是在上一层数据集里面再抽取一个数据集.
GridViewDemo1.DataSource = query.Skip(10).Take(10);
结果:
看看使用SQL的变化,就更容易理解这一点:
单纯的query:
SELECT [t0].[ProductID], [t0].[ProductName], (
SELECT SUM(CONVERT(Int,[t3].[Quantity]))
FROM [dbo].[Order Details] AS [t3]
WHERE [t3].[ProductID] = [t0].[ProductID]
) AS [value], (
SELECT SUM((CONVERT(Decimal(29,4),[t4].[Quantity])) * [t4].[UnitPrice])
FROM [dbo].[Order Details] AS [t4]
WHERE [t4].[ProductID] = [t0].[ProductID]
) AS [value2]
FROM [dbo].[Products] AS [t0]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Categories] AS [t1], [dbo].[Products] AS [t2]
WHERE ([t1].[CategoryID] = [t0].[CategoryID]) AND ([t2].[CategoryID] = [t1].[CategoryID])
)) > 5
加上skip和take:
SELECT TOP 10 [t6].[产品ID], [t6].[产品名字], [t6].[总数], [t6].[总收入]
FROM (
SELECT ROW_NUMBER() OVER (ORDER BY [t3].[ProductID], [t3].[ProductName], [t3].[value], [t3].[value2]) AS [ROW_NUMBER], [t3].[ProductID] AS [产品ID], [t3].[ProductName] AS [产品名字], [t3].[value] AS [总数], [t3].[value2] AS [总收入]
FROM (
SELECT [t0].[ProductID], [t0].[ProductName], (
SELECT SUM(CONVERT(Int,[t1].[Quantity]))
FROM [dbo].[Order Details] AS [t1]
WHERE [t1].[ProductID] = [t0].[ProductID]
) AS [value], (
SELECT SUM((CONVERT(Decimal(29,4),[t2].[Quantity])) * [t2].[UnitPrice])
FROM [dbo].[Order Details] AS [t2]
WHERE [t2].[ProductID] = [t0].[ProductID]
) AS [value2], [t0].[CategoryID]
FROM [dbo].[Products] AS [t0]
) AS [t3]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Categories] AS [t4], [dbo].[Products] AS [t5]
WHERE ([t4].[CategoryID] = [t3].[CategoryID]) AND ([t5].[CategoryID] = [t4].[CategoryID])
)) > 5
) AS [t6]
WHERE [t6].[ROW_NUMBER] > 10
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