2个要点:
1.linq操作的集合必须实现IEnumerable接口,所以在这3.0之前为实现该接口的集合需通过Cast或TypeOf方法转换成可Linq的集合;
2.查询式和Lame那啥表达式都可以一起使用.那个方便用哪个,他们只在第一次使用时才会真正去查询;
List<Employee> ils = new List<Employee>()
{
new Employee(){IDCode="jack5",Age=20,littleName="ab"},
new Employee(){IDCode="mike444",Age=12,littleName="aa"},
new Employee(){IDCode="mary5",Age=12,littleName="zs"},
new Employee(){IDCode="sm5555",Age=67,littleName="yb"},
new Employee(){IDCode="som",Age=67,littleName="cr"}
}; ArrayList als = new ArrayList()
{
new Department(){Name="jack",DepName="富士康"},
new Department(){Name="jack",DepName="華為"},
new Department(){Name="mary",DepName="騰訊"},
new Department(){Name="sum",DepName="移動"},
new Department(){Name="soom",DepName="聯通"}
}; #region 查詢語句 第三章,linq技術詳解
//帶有Into的group by語句
var va = from c in ils
group c by new { c.littleName, c.Age } into g
select new { Name = g.Key, ageC = g.Count() };
var va1 = ils.GroupBy(p => new { p.littleName, p.Age }).Select(p => new { name = p.Key, agec = p.Count() }); //顯示枚舉變量類型
var varT = from c in ils
join Department d in als on c.IDCode equals d.Name
select new { age = c.Age, depName = d.DepName };
var varT1 = ils.Join(als.Cast<Department>(), c => c.IDCode, p => p.Name, (c, p) => new { age = c.Age, depName = p.DepName }); //join語句
var varJoin = from c in ils
join Department d in als
on c.IDCode equals d.Name
into ao
select new { c.IDCode, sum = ao.Sum(p => p.DepName.Length) };
var varJoin1 = ils.GroupJoin(als.Cast<Department>(), a => a.IDCode, b => b.Name, (b, a) => new { b.IDCode, sum = a.Count() }); //Let和Where語句
var varLet = from c in ils
let names = c.IDCode + ":" + c.littleName
where names.Length > 5
select new { c.Age, names };
var varLet1 = ils.Select(a => new { a, names = a.IDCode + ":" + a.littleName })
.Where(p => p.names.Length > 5)
.Select(b => new { b.a.Age, b.names }); //Generator語句(多個 from),orderby語句
var varSelMany = from a in ils
from b in als.Cast<Department>()
orderby a.Age, a.Department descending
select new { a.IDCode, a.littleName, a.Age, b.DepName };
var varSelMany1 = ils.SelectMany(p => als.Cast<Department>().Select(a => new { p.Age, a.DepName })).OrderByDescending(a => a.Age).ThenByDescending(a => a.DepName); //group by
var varGroup = from p in ils
group p by p.Age
into a
select a.Key + ":" + als.Capacity; #endregion #region 延遲操作符詳解
//異常都是ArgumentNullException
//select,where都有兩個原型,另一個原型有索引參數
var varWhere = ils.Where((p, i) => i < 2); //分區操作符 take
var varTake = ils.Take(2); //TakeWhile 只要條件不符合就會跳出
var varTakeWhile = ils.TakeWhile((p, q) => p.IDCode.Length > 4); //skip 與take互補
var varSkip = ils.Skip(2); //skipwhile 與takewhile互補
var varSkipWhile = ils.SkipWhile((a, i) => a.IDCode.Length > 5 && i < 3); //串聯操作符
var varConcat = ils.Take(2).Concat(ils.Skip(2));
//concat只可以串聯兩個序列,當串聯多個序列的時候可以用SelectMany;
var varSelectMany1 = new[] { ils.Take(1), ils.Skip(1) }.SelectMany(s => s); //排序操作,第二個原型可以加參數,比較器,二次排序用thenby,orderbydesding類似
var varOrderby = ils.OrderBy(p => p.IDCode.Length); //reverse相反序列輸出
//Join和JoinGroup p119
IEnumerable<IGrouping<string,Employee>> items = ils.GroupBy(p => p.littleName);
IEnumerable<IGrouping<string,Department>> items1= ils.GroupBy(p => p.IDCode, q => q.Department); //集合操作符 distinct,union(并集區別于Concat),intersect(連接后重複元素的序列),except(刪除參數中與自己重複的元素)
var ca = ils.Distinct();
List<Employee> ils1 = ils.Take(2).ToList<Employee>();
ils1.Add(new Employee() { IDCode = "我加的", Age = 33, littleName = "xixi" });
foreach (var v in ils.Except(ils1))
{
Console.WriteLine(v.littleName);
} //元素操作符
var ilsDefaultIfEmpty = ils.Where(p => p.IDCode == "hehe").DefaultIfEmpty().First();
var ilsDefaultIfEmpty1 = ils.Where(p => p.IDCode == "hehe").DefaultIfEmpty(new Employee() { IDCode="heheid"}).First(); //生成操作符 Enumerable靜態方法Range,Repeat,
IEnumerable<int> EnumRange = Enumerable.Range(2, 20);
foreach (int i in EnumRange)
{
Console.WriteLine(i);
}
//p145 string str = string.Empty;
//cast,ofType,AsEnumerable()[將序列編程序列,適用于Linq To Sql] #endregion