(精华)2020年8月11日 C#基础知识点 Linq To Object的使用
(精华)2020年8月11日 C#基础知识点 Linq To Object的使用
/// <summary>
/// Linq To Object
/// .NetFramework3.0的一个非常重大的改变
/// Linq专门用来做数据处理
/// </summary>
public class LinqShow
{<!-- -->
#region Data Init
private List<Student> GetStudentList()
{<!-- -->
#region 初始化数据
List<Student> studentList = new List<Student>()
{<!-- -->
new Student()
{<!-- -->
Id=1,
Name="赵亮",
ClassId=2,
Age=35
},
new Student()
{<!-- -->
Id=1,
Name="再努力一点",
ClassId=2,
Age=23
},
new Student()
{<!-- -->
Id=1,
Name="王炸",
ClassId=2,
Age=27
},
new Student()
{<!-- -->
Id=1,
Name="疯子科学家",
ClassId=2,
Age=26
},
new Student()
{<!-- -->
Id=1,
Name="灭",
ClassId=2,
Age=25
},
new Student()
{<!-- -->
Id=1,
Name="黑骑士",
ClassId=2,
Age=24
},
new Student()
{<!-- -->
Id=1,
Name="故乡的风",
ClassId=2,
Age=21
},
new Student()
{<!-- -->
Id=1,
Name="晴天",
ClassId=2,
Age=22
},
new Student()
{<!-- -->
Id=1,
Name="旭光",
ClassId=2,
Age=34
},
new Student()
{<!-- -->
Id=1,
Name="oldkwok",
ClassId=2,
Age=30
},
new Student()
{<!-- -->
Id=1,
Name="乐儿",
ClassId=2,
Age=30
},
new Student()
{<!-- -->
Id=1,
Name="暴风轻语",
ClassId=2,
Age=30
},
new Student()
{<!-- -->
Id=1,
Name="一个人的孤单",
ClassId=2,
Age=28
},
new Student()
{<!-- -->
Id=1,
Name="小张",
ClassId=2,
Age=30
},
new Student()
{<!-- -->
Id=3,
Name="阿亮",
ClassId=3,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="37度",
ClassId=4,
Age=30
}
,
new Student()
{<!-- -->
Id=4,
Name="关耳",
ClassId=4,
Age=30
}
,
new Student()
{<!-- -->
Id=4,
Name="耳机侠",
ClassId=4,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="Wheat",
ClassId=4,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="Heaven",
ClassId=4,
Age=22
},
new Student()
{<!-- -->
Id=4,
Name="等待你的微笑",
ClassId=4,
Age=23
},
new Student()
{<!-- -->
Id=4,
Name="畅",
ClassId=4,
Age=25
},
new Student()
{<!-- -->
Id=4,
Name="混无痕",
ClassId=4,
Age=26
},
new Student()
{<!-- -->
Id=4,
Name="37度",
ClassId=4,
Age=28
},
new Student()
{<!-- -->
Id=4,
Name="新的世界",
ClassId=4,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="Rui",
ClassId=4,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="帆",
ClassId=4,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="肩膀",
ClassId=4,
Age=30
},
new Student()
{<!-- -->
Id=4,
Name="孤独的根号三",
ClassId=4,
Age=30
}
};
#endregion
return studentList;
}
#endregion
public void Show()
{<!-- -->
List<Student> studentList = this.GetStudentList();
{<!-- -->
var list = new List<Student>();
//第一种
foreach (var item in studentList)
{<!-- -->
if (item.Age < 30)
{<!-- -->
list.Add(item);
}
}
//第二种
list = ExtendMethod.JerryWhere(studentList, a => a.Age < 30);
//第三种
list = studentList.JerryWhere(a => a.Age < 30);
}
{<!-- -->
//N个条件叠加 随着判断条件的不同，那么就需要编写非常多的代码
var list = new List<Student>();
foreach (var item in studentList)
{<!-- -->
if (item.Id > 1
&& item.Name != null
&& item.ClassId == 1
&& item.Age > 20)
{<!-- -->
list.Add(item);
}
}
list = studentList.JerryWhere(item => item.Id > 1
&& item.Name != null
&& item.ClassId == 1
&& item.Age > 20);
}
#region Linq 扩展方法&表达式
{<!-- -->
var list = studentList.Where<Student>(s => s.Age < 30);
foreach (var item in list)
{<!-- -->
Console.WriteLine("Name={0} Age={1}", item.Name, item.Age);
}
}
{<!-- -->
var list = from s in studentList
where s.Age < 30
select s;
foreach (var item in list)
{<!-- -->
Console.WriteLine("Name={0} Age={1}", item.Name, item.Age);
}
}
#endregion
#region linq to object
{<!-- -->
Console.WriteLine("********************");
var list = studentList.Where<Student>(s => s.Age < 30)
.Select(s => new
{<!-- -->
IdName = s.Id + s.Name,
ClassName = s.ClassId == 2 ? "高级班" : "其他班"
});
foreach (var item in list)
{<!-- -->
Console.WriteLine("Name={0} Age={1}", item.ClassName, item.IdName);
}
}
{<!-- -->
Console.WriteLine("********************");
var list = from s in studentList
where s.Age < 30
select new
{<!-- -->
IdName = s.Id + s.Name,
ClassName = s.ClassId == 2 ? "高级班" : "其他班"
};
foreach (var item in list)
{<!-- -->
Console.WriteLine("Name={0} Age={1}", item.ClassName, item.IdName);
}
}
{<!-- -->
Console.WriteLine("********************");
var list = studentList.Where<Student>(s => s.Age < 30)//条件过滤
.Select(s => new//投影
{<!-- -->
Id = s.Id,
ClassId = s.ClassId,
IdName = s.Id + s.Name,
ClassName = s.ClassId == 2 ? "高级班" : "其他班"
})
.OrderBy(s => s.Id)//排序
.OrderByDescending(s => s.ClassId)//倒排
.Skip(2)//跳过几条
.Take(3)//获取几条
;
foreach (var item in list)
{<!-- -->
Console.WriteLine($"Name={item.ClassName} Age={item.IdName}");
}
}
{<!-- -->//group by
Console.WriteLine("********************");
var list = from s in studentList
where s.Age < 30
group s by s.ClassId into sg
select new
{<!-- -->
key = sg.Key,
maxAge = sg.Max(t => t.Age)
};
foreach (var item in list)
{<!-- -->
Console.WriteLine($"key={item.key} maxAge={item.maxAge}");
}
//group by new {s.ClassId,s.Age}
//group by new {A=s.ClassId>1}
}
{<!-- -->
Console.WriteLine("********************");
var list = studentList.GroupBy(s => s.ClassId).Select(sg => new
{<!-- -->
key = sg.Key,
maxAge = sg.Max(t => t.Age)
});
foreach (var item in list)
{<!-- -->
Console.WriteLine($"key={item.key} maxAge={item.maxAge}");
}
}
List<Class> classList = new List<Class>()
{<!-- -->
new Class()
{<!-- -->
Id=1,
ClassName="初级班"
},
new Class()
{<!-- -->
Id=2,
ClassName="高级班"
},
new Class()
{<!-- -->
Id=3,
ClassName="微信小程序"
},
};
{<!-- -->
var list = from s in studentList
join c in classList on s.ClassId equals c.Id
select new
{<!-- -->
Name = s.Name,
CalssName = c.ClassName
};
foreach (var item in list)
{<!-- -->
Console.WriteLine($"Name={item.Name},CalssName={item.CalssName}");
}
}
{<!-- -->
var list = studentList.Join(classList, s => s.ClassId, c => c.Id, (s, c) => new
{<!-- -->
Name = s.Name,
CalssName = c.ClassName
});
foreach (var item in list)
{<!-- -->
Console.WriteLine($"Name={item.Name},CalssName={item.CalssName}");
}
}
{<!-- -->//左连接
var list = from s in studentList
join c in classList on s.ClassId equals c.Id
into scList
from sc in scList.DefaultIfEmpty()
select new
{<!-- -->
Name = s.Name,
CalssName = sc == null ? "无班级" : sc.ClassName//c变sc，为空则用
};
foreach (var item in list)
{<!-- -->
Console.WriteLine($"Name={item.Name},CalssName={item.CalssName}");
}
Console.WriteLine(list.Count());
}
{<!-- -->
var list = studentList.Join(classList, s => s.ClassId, c => c.Id, (s, c) => new
{<!-- -->
Name = s.Name,
CalssName = c.ClassName
}).DefaultIfEmpty();//为空就没有了
foreach (var item in list)
{<!-- -->
Console.WriteLine($"Name={item.Name},CalssName={item.CalssName}");
}
Console.WriteLine(list.Count());
}
#endregion
}
}
