linq查询

1、多条件查询：
并且 &&
或者 ||

var list = con.car.Where(r => r.code == "c014" || r.oil == 8.2m);

2、模糊查询
1.模糊
var list = con.car.Where(r => r.name.Contains("AT"));//contains包含
2.开头
var list = con.car.Where(r => r.name.StartsWith("皇冠"));//startswith以什么开头
3.结尾
var list = con.car.Where(r => r.name.EndsWith("版"));//endswith以什么结尾


3、统计查询
1.总个数
//var count = con.car.Count();
2.最大值
//var Max = con.car.Max(r => r.price);
3.最小值
//var Min = con.car.Min(r => r.price);
4.平均值
//var avg = con.car.Average(r => r.price);

4、分页查询
跳过，获取
int count = 5;//一页显示多少条
int pagecount = 1;//第几页

var list = con.car.Skip(pagecount * count).Take(count);//skip：跳过多少条。take：取多少条

5、排序查询
升序
//var list = con.car.OrderBy(r => r.price);
降序
//var list = con.car.OrderByDescending(r => r.price);

去重：
var aaa = con.car.Select(r => r.oil).Distinct();

6、外键显示
return this.brand1.brand_name;//brand1是外键表名，与主键表列重名，自动加一

7、组合查询
var list1 = con.car.AsQueryable();
var list2 = con.car.AsQueryable();
var list3 = con.car.AsQueryable();

if (TextBox1.Text.Trim().Length > 0)
{
list1 = list1.Where(r => r.name.Contains(TextBox1.Text.Trim()));
}
if (TextBox2.Text.Trim().Length > 0)
{
list2 = list2.Where(r => r.brand1.brand_name.Contains(TextBox2.Text.Trim()));
}
if (TextBox3.Text.Trim().Length > 0)
{
list3 = list3.Where(r => r.oil == Convert.ToDecimal(TextBox3.Text.Trim()));
}

var list = list1.Intersect(list2).Intersect(list3);

交集
var list = list1.Intersect(list2).Intersect(list3);
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Repeater1.DataSource = list;
Repeater1.DataBind();