Linq learning summary 1-refer to the detailed description of Linq technology, 1-linq

Linq learning summary 1-refer to the detailed description of Linq technology, 1-linq

Two key points:

1. The set of linq operations must implement the IEnumerable interface. Therefore, before 3.0, the set that implements this interface must be converted to a Linq-enabled set through the Cast or TypeOf method;

2. the query expression and the Lame expression can be used together. Which one is convenient to use? They only query the expression for the first time;

 

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 = "Foxconn"}, new Department () {Name = "jack", DepName = "translated as"}, new Department () {Name = "mary", DepName = "updated employee"}, new Department () {Name = "sum", DepName = ""}, new Department () {Name = "soom", DepName = ""}}; # chapter 3 of the region query sentence, using the nested grouping solution in the linq technique // The group by clause with Into 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 ()}); // The variable type 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 an alias 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 =>. IDCode, B => B. name, (B, a) => new {B. IDCode, sum =. count ()}); // Let and Where statement 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 =. IDCode + ":" +. littleName }). where (p => p. names. length> 5 ). select (B => new {B. a. age, B. names}); // Generator sentence (multiple from), orderby sentence var varSelMany = from a in ils from B in als. cast <Department> () orderby. age,. department descending select new {. IDCode,. littleName,. age, B. depName}; var varSelMany1 = ils. selectals (p => als. cast <Department> (). select (a => new {p. age,. depName })). orderByDescending (a =>. age ). thenByDescending (a =>. depName); // group by var varGroup = from p in ils group p by p. age into a select. key + ":" + als. capacity; # endregion # solution of region extension operator // always returns ArgumentNullException // select, where has two prototypes, another prototype has index indexes var varWhere = ils. where (p, I) => I <2); // The partition operator take var varTake = ils. take (2); // TakeWhile will jump out of var varTakeWhile = ils as long as the condition does not match. takeWhile (p, q) => p. IDCode. length> 4); // The skip and take parameters var varSkip = ils. skip (2); // The skipwhile and takewhile parameters var varSkipWhile = ils. skipWhile (a, I) =>. IDCode. length> 5 & I <3); // string signature operator var varConcat = ils. take (2 ). concat (ils. skip (2); // concat can be a string of only two sequences. When a string contains multiple sequences, selectsequence can be used; var varSelectMany1 = new [] {ils. take (1), ils. skip (1 )}. selectsort (s => s); // sorting operation. The second prototype can be used to add the number of neighbors. For secondary sorting, thenby and orderbydesding are similar to var varOrderby = ils. orderBy (p => p. IDCode. length); // reverse sequence of reverse sort out // Join and 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); // set operator distinct, union (union region is different from Concat), intersect (sequence of re-Attention elements after concatenation ), partition T (excluding the elements in the Partition Number and their own duplicates) var ca = ils. distinct (); List <Employee> ils1 = ils. take (2 ). toList <Employee> (); ils1.Add (new Employee () {IDCode = "I added", Age = 33, littleName = "xixi "}); foreach (var v in ils. failed T (ils1) {Console. writeLine (v. littleName);} // element operator var ilsDefaultIfEmpty = ils. where (p => p. IDCode = "hehe "). defaultIfEmpty (). first (); var ilsDefaultIfEmpty1 = ils. where (p => p. IDCode = "hehe "). defaultIfEmpty (new Employee () {IDCode = "heheid "}). first (); // generate the operator Enumerable random between methods 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 (