lambda表达式多条件查询
并且,与或者:&&与||
clist = clist.Where(r => r.Price > 50 && r.Price < 60 || r.Price < 30).ToList();
包含:contains
List<car> clist= new cardata().SelectAll().Where(r => r.Name.Contains(TextBox1.Text)).ToList();
等于:==
clist = clist.Where(r => r.Price==40).ToList();
clist = clist.Where(r => r.Price.Equals(40)).ToList();
以。。开始、以。。结束
List<users> ulist = con.users.Where(r => r.username.StartsWith("s")).ToList();
List<users> ulsit = con.users.Where(r => r.username.EndsWith("t")).ToList();
最大值、最小值、平均值、求和
int s = con.users.Max(r=>r.ids);
int t = con.users.Min(r=>r.ids);
double h = con.users.Average(r => r.ids);
int d = con.users.Sum(r => r.ids);
求交集
List<users> ulist1 = new List<users>();
List<users> ulist2 = new List<users>();
List<users> ulist3 = new List<users>();
List<users> ulist = ulist1.Intersect(ulist2).Intersect(ulist3).ToList();
顺序、倒序
List<users> ulist = con.users.OrderBy(r => r.ids).ToList();
List<users> ulist1 = con.users.OrderByDescending(r => r.ids).ToList();
//******* 对集合按Name属于进行分组GroupBy查询 ********
//结果中包括的字段:
//1、分组的关键字:Name = g.Key
//2、每个分组的数量:count = g.Count()
//3、每个分组的年龄总和:ageC = g.Sum(item => item.Age)
//4、每个分组的收入总和:moneyC = g.Sum(item => item.Money)
//写法1:Lambda 表达式写法(推荐)
var ls = persons1.GroupBy(a => a.Name).Select(g => (new { name = g.Key, count = g.Count(), ageC = g.Sum(item => item.Age), moneyC = g.Sum(item => item.Money) }));
//写法2:类SQL语言写法 最终编译器会把它转化为lamda表达式
var ls2 = from ps in persons1
group ps by ps.Name
into g
select new { name = g.Key, count = g.Count(), ageC = g.Sum(item => item.Age), moneyC = g.Sum(item => item.Money) };
dataGridView1.DataSource = ls.ToList();
//dataGridView1.DataSource = ls2.ToList();
}
List.Where(new Func<Class, bool>(Where));
private bool Where(Class c)
{
//组织表达式,返回bool
}
Expression<Func<XXX, bool>> expression = t => true;
expression = expression.And(t => t.AAA == 1);
expression = expression.And(t => t.BBB > 1);
var ds = products.AsQueryable().Where(expression).ToList();
public static class PredicateExtensions
{
public static Expression<Func<T, bool>> True<T>()
{
return f => true;
}
public static Expression<Func<T, bool>> False<T>()
{
return f => false;
}
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
{
var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);
}
public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
{
var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);
}
}
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