using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms; namespace 练习LinQ入门
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private mydbDataContext context = new mydbDataContext(); private void Form1_Load(object sender, EventArgs e)
{
FillInfo();
cbx_sex.SelectedIndex = ;
} private void FillInfo()
{
//法一：
//List<Info> list = context.Info.ToList();
//dataGridView1.DataSource = list;
//法二：
//var query = from p in context.Info select p;
//dataGridView1.DataSource = query;
//法三：
var query = context.Info;
dataGridView1.DataSource = query;
} private void btn_ADD_Click(object sender, EventArgs e)
{
Info data = new Info();
data.Code = txt_code.Text;
data.Name = txt_name.Text;
data.Nation = txt_nation.Text;
data.Sex = Convert.ToBoolean(txt_sex.Text);
data.Birthday = Convert.ToDateTime(txt_b.Text); context.Info.InsertOnSubmit(data);
context.SubmitChanges();//提交
FillInfo();
} private void button2_Click(object sender, EventArgs e)
{
var query = from p in context.Info where p.Code == txt_code.Text select p;
if (query.Count() > )
{
// query.Single();//第一条
Info data = query.First();
context.Info.DeleteOnSubmit(data);
context.SubmitChanges();
}
FillInfo(); //Form p in context.Info where
// Info data = context.Info.Where( => );
} private void button1_Click(object sender, EventArgs e)
{
var a = from p in context.Info where p.Code == txt_code.Text select p;
if (a.Count() > )
{
Info data = a.First();
data.Name = txt_name.Text;
data.Sex = Convert.ToBoolean(txt_sex.Text);
data.Nation = txt_nation.Text;
data.Birthday = Convert.ToDateTime(txt_b.Text);
context.SubmitChanges();
}
FillInfo();
} private void btn_select_Click(object sender, EventArgs e)
{ #region meiyong
//// e.Equals();
//Type t = e.GetType();
////t.GetProperties();
////t.GetMethods();
//Type s = sender.GetType();
#endregion
Button btn = (Button)sender;
if (btn.Name == "btn_select")
{
if (tbx_code2.Text != "")
{
//单条件等值查询
//var query = from p in context.Info where p.Code == tbx_code2.Text.Trim() select p; var query = context.Info.Where(p => p.Code == tbx_code2.Text.Trim());//扩展方法 Lambda表达式
dataGridView1.DataSource = query;
}
}
else if (btn.Name == "btn_select2")
{
if (tbx_code2.Text != "")
{
//单条件不等值查询
//var query = from p in context.Info where p.Code != tbx_code2.Text.Trim() select p;
//>= <= 同样可以用于筛选
var query = context.Info.Where(p => p.Code != tbx_code2.Text.Trim());
dataGridView1.DataSource = query;
}
}
else if (btn.Name == "btn_duo")
{
//多条件查询
var query = from p in context.Info where p.Sex == Convert.ToBoolean(cbx_sex.Text.Trim()) && p.Birthday.Value.Year > Convert.ToInt32(tbx_b_duo.Text.Trim()) select p;
//或者
//var query1 = context.Info.Where(p => p.Sex == Convert.ToBoolean(cbx_sex.Text.Trim()) && p.Birthday.Value.Year > Convert.ToInt32(tbx_b_duo.Text.Trim()));
//var a=context.Info.Where (p=>p.Sex==Convert.ToBoolean(cbx_sex.Text.Trim())).Where(p=>p.Birthday.Value.Year> Convert.ToInt32(tbx_b_duo.Text.Trim()));//链式表达式 （&& 逻辑与可以用）
dataGridView1.DataSource = query;
}
else if (btn.Name == "btn_select_*")
{
//var query = from p in context.Info where p.Name.Contains(tbx_xing.Text.Trim()) select p;//相当于like'%某'
//var query = from p in context.Info where p.Name.StartsWith(tbx_xing.Text.Trim()) select p;//以什么开头
//var query = from p in context.Info where p.Name.EndsWith(tbx_xing.Text.Trim()) select p;//以什么结尾
//var query = from p in context.Info where p.Name.Substring(1, tbx_xing.TextLength) == tbx_xing.Text.Trim() select p;//截取第一位往后
var query = context.Info.Where(p => p.Name.StartsWith(tbx_xing.Text.Trim())); dataGridView1.DataSource = query;
}
else if (btn.Name == "btn_shua")
{
FillInfo();
}
else if (btn.Name == "btn_jiao")
{
//交集相当于逻辑与 取公共部分
var p1 = from p in context.Info where p.Sex == true select p;
var p2 = context.Info.Where(p => p.Birthday.Value.Year > );
var query = p1.Intersect(p2);
dataGridView1.DataSource = query;
}
else if (btn.Name == "btn_bing")
{
//并集相当于逻辑或
var p1 = from p in context.Info where p.Sex == true select p;
var p2 = context.Info.Where(p => p.Birthday.Value.Year > );
var query = p1.Union(p2);
dataGridView1.DataSource = query;
}
else if (btn.Name == "btn_bu")
{
//差集 从一个集合减去另外一个集合 看谁减谁
var p1 = from p in context.Info where p.Sex == true select p;
var p2 = context.Info.Where(p => p.Birthday.Value.Year > );
var query = p1.Except(p2);
dataGridView1.DataSource = query;
} } private void btn_jige_Click(object sender, EventArgs e)
{
Button btn =(Button)sender;
if (btn.Name=="btn_jige")
{
var query = context.Info.Where(p => p.Birthday.Value.Year > );
this.Text = query.Count().ToString();//个数
}
else if (btn.Name=="btn_sum")
{
var query = context.Info.Where(p => p.Birthday.Value.Year > );
this.Text = query.Sum(p=>DateTime.Now.Year-p.Birthday.Value.Year).ToString();//求和
}
else if (btn.Name == "btn_avg")
{
var query = context.Info.Where(p => p.Birthday.Value.Year > );
this.Text = query.Average(p => DateTime.Now.Year - p.Birthday.Value.Year).ToString();//求平均值
} } private void button5_Click(object sender, EventArgs e)
{
var query = context.Info.Where(p => p.Birthday.Value.Year > );
List<Info> list = query.ToList();//转集合
dataGridView1.DataSource = list;
} private void button7_Click(object sender, EventArgs e)
{
var query = context.Info.Where(p => p.Birthday.Value.Year > );
Info[] list = query.ToArray();//转数组
dataGridView1.DataSource = list;
} private void button6_Click(object sender, EventArgs e)
{
var query = context.Info.Where(p => p.Birthday.Value.Year > );
//Info data = query.Single();//单一
Info data = query.First();
dataGridView1.DataSource = data;
} private void button3_Click(object sender, EventArgs e)
{
//每页多少条pagesize，要找第几页pageno
var query=context.Info.Skip(*).Take();//skip跳过多少行，take取多少行
dataGridView1.DataSource=query;
} }
}
练习源码：http://pan.baidu.com/s/1c0wJ8i8
LinQ to sql 入门小教程：http://pan.baidu.com/s/1dD2NkcD
1.查询所有的
var query = from p in _Context.Info select p;
var query = _Context.Info;
2.单条件查询
等值查
var query = from p in _Context.Info where p.Code == "p002" select p;
注意：双等号，双引号。---C#语法。
var query = _Context.Info.Where(p => p.Code == "p002" ); //Lambda表达式
不等值查
//var query = from p in _Context.Info where p.Code != "p002" select p;
//var query = _Context.Info.Where(p => p.Code != "p002"); //Lambda表达式
//var query = from p in _Context.Info where p.Birthday.Value.Year > 1985 select p;
var query = _Context.Info.Where(p=>p.Birthday.Value.Year < 1985);
3.多条件查询
//var query = from p in _Context.Info where p.Sex == true && p.Birthday.Value.Year > 1985 select p;
//var query = _Context.Info.Where(p=>p.Sex==true && p.Birthday.Value.Year>1985);
var query = _Context.Info.Where(p => p.Sex == true).Where(p=>p.Birthday.Value.Year>1985) ; //多条件逻辑与可以用链式表达式写
4.模糊查询
//var query = from p in _Context.Info where p.Name.Contains("张") select p; //相当于like '%张%'
//var query = from p in _Context.Info where p.Name.StartsWith("张") select p; // like '张%'
//var query = from p in _Context.Info where p.Name.EndsWith("张") select p; //like '%张'
//var query = from p in _Context.Info where p.Name.Substring(1,1) == "张" select p;// like '_张%'
var query = _Context.Info.Where(p => p.Name.StartsWith("张"));
5.集合操作
var q1 = from p in _Context.Info where p.Sex== true select p;
var q2 = _Context.Info.Where(p => p.Birthday.Value.Year > 1985);
交
var query = q1.Intersect(q2);
并
var query = q1.Union(q2);
差
var query = q2.Except(q1);
6.统计函数：
var query = _Context.Info.Where(p => p.Birthday.Value.Year > 1985);
//this.Text = query.Count().ToString();
//this.Text = query.Sum(p=>DateTime.Now.Year - p.Birthday.Value.Year).ToString();
//this.Text = query.Average(p => DateTime.Now.Year - p.Birthday.Value.Year).ToString();
//this.Text = query.Max(p => DateTime.Now.Year - p.Birthday.Value.Year).ToString();
this.Text = query.Min(p => DateTime.Now.Year - p.Birthday.Value.Year).ToString();
7.转换操作
ToList(),ToArray(),First()/Single()
8.分页
var query = _Context.Info.Skip(2*2).Take(2);
这里主要是将数据库中的常用操作用LAMBDA表达式重新表示了下，用法不多，但相对较常用，等有时间了还会扩展，并将查询语句及LINQ到时也一并重新整理下：
.select语句：books.Select(p=>new { p.Title, p.UnitPrice, p.Author});//需用匿名方式
.where语句：books.Where(p=>p.UnitPrice==&&p.Title=”ABC”);
补充：
像数据库中的LIKE ‘%c++%’，LAMBDA中用p.Title.Contains(“c++”)表示；
像数据库中的LIKE ‘c%’，LAMBDA中用p.Title.StartWith(“c”)表示；
像数据库中的LIKE ‘%c’，LAMBDA中用p.Title.EndsWith(“c”)表示；
Where的另一种表现形式：
books.Where(p=>{
var ret = p.UnitPrice>&&p.Title.Contains(“c++”);
return ret;
});
.排序语句：
像数据库中order by 升序：
通过 “对象.OrderBy(p=>p.UnitPrice)”实现
像数据库中order by 降序：
通过 “对象.OrderByDescending(p=>p.UnitPrice)”实现
像数据库中order by UnitPrice desc，Title asc：
通过 ”对象.OrderByDescending(p=>p.UnitPrice).ThenBy(p=>p.Title)”
反过来则是： ”对象.OrderBy(p=>p.UnitPrice).ThenByDescending(p=>p.Title)”
.组函数：
var max = books.Where(p => p.CategoryId == ).Max(p => p.UnitPrice);
var min = books.Min(p => p.UnitPrice);
var count = books.Count( );
var avg = books.Average(p => p.UnitPrice);
var sum = books.Sum(p => p.UnitPrice);
注意，上面这些获得的东西，不是对象，是单个值
. GROUP BY函数
// select categoryid,max(unitpirce) from books group by categoryid having max(unitprice)>50
var list6 = books.GroupBy(p => p.CategoryId).Where(p=>p.Max(q=>q.UnitPrice)>);
foreach (var item in list6)
{
Response.Write(string.Format("类别编号:{0},最高价{1} ",
item.Key,item.Max(p=>p.UnitPrice)));
}
. TOP函数
//取一个范围 如3,5
var list7 = books.Skip().Take().Select(p => new { p.Title, p.CategoryId, p.UnitPrice });
// select top 5
var list7 = books.Take().OrderByDescending(p => p.UnitPrice)
.Select(p => new { p.CategoryId, p.UnitPrice, p.Title, p.Author });
.union 函数
books.Where(p => p.CategoryId == ).Select(p => new { p.CategoryId, p.UnitPrice, p.Title, p.Author }).Union(books.Where(p => p.CategoryId == ).Select(p => new { p.CategoryId, p.UnitPrice, p.Title, p.Author }));
这里的Select子句中的列需对应，跟数据库中是一样的
.Join方法，用于实现数据库中双表连接查询
//select a.title,a.unitprice,a.categoryid,b.id,b.name from books a,category b
//where a.categoryid=b.id and b.name=‘数据库’
books.Join(cates.Where(m => m.Name == "数据库"),p => p.CategoryId, q => q.ID, (a, b) => new { a.Title, a.UnitPrice, a.CategoryId, b.ID, b.Name });
说明：
Join()方法的调用对象类似于在SQL语句中第一张表的表名
而Join()方法的第一个形参是第二张表表名的Where条件
Join()方法的第二和第三个参数分别表示第一张表与第二张表的关联字段
Join()方法的第四个参数表示从两表中需要获取的字段，(a, b)分别表示第一张表和第二张表
http://blog.csdn.net/codefighting/article/details/7048966
.AsEnumerable()是延迟执行的，实际上什么都没有发生，当真正使用对象的时候（例如调用：First, Single, ToList....的时候）才执行。
下面就是.AsEnumerable()与相对应的.AsQueryable()的区别：
AsEnumerable将一个序列向上转换为一个IEnumerable, 强制将Enumerable类下面的查询操作符绑定到后续的子查询当中。
AsQueryable将一个序列向下转换为一个IQueryable, 它生成了一个本地查询的IQueryable包装。
- .AsEnumerable()延迟执行，不会立即执行。当你调用.AsEnumerable()的时候，实际上什么都没有发生。
- .ToList()立即执行
- 当你需要操作结果的时候，用.ToList()，否则，如果仅仅是用来查询不需要进一步使用结果集，并可以延迟执行，就用.AsEnumerable()/IEnumerable /IQueryable
- .AsEnumerable()虽然延迟执行，但还是访问
数据库，而.ToList()直接取得结果放在内存中。比如我们需要显示两个部门的员工时，部门可以先取出放置在List中，然后再依次取出各个部门的员
工，这时访问的效率要高一些，因为不需要每次都访问数据库去取出部门。 - IQueryable实现了IEnumberable接口。但IEnumerable<T> 换成IQueryable<T>后速度提高很多。原因：
- IQueryable接口与IEnumberable接口
的区别： IEnumerable<T> 泛型类在调用自己的SKip 和 Take
等扩展方法之前数据就已经加载在本地内存里了，而IQueryable<T> 是将Skip ,take
这些方法表达式翻译成T-SQL语句之后再向SQL服务器发送命令，它并不是把所有数据都加载到内存里来才进行条件过滤。 - IEnumerable跑的是Linq to Object，强制从数据库中读取所有数据到内存先。