Linq基本语法.doc

Linq基本语法2010Linq基本语法1Linq基本语法2一、LINQ查询符列表5二、使用Enumerable获取Counts6三、定义演示的实例6四、LINQ语法7五、使用LINQ查询结果9Linq基本语法varresult=fromitemincontainerorderbyvalueascending/descendingselectitem; 1、获取全部记录varallCars=fromcinmyCarsselectc; 2、只获取字段名称varnames=fromcinmyCarsselectc.PetName; 这里names就是隐式类型的变量。3、使用Enumerable.Distinct()varmakes=(fromcinmyCarsselectc.Make).Distinct(); 4、即可以在定义的时候调用Enumberalbe扩展函数varnames=fromcinmyCarsselectc.PetName; foreach(varninnames) Console.WriteLine(Name:0,n); 也可以在兼容的数组类型上调用varmakes=fromcinmyCarsselectc.Make; Console.WriteLine(Distinctmakes:); foreach(varminmakes.Distinct() Console.WriteLine(Make:0,m); /NowgetonlytheBMWs. varonlyBMWs=fromcinmyCarswherec.Make=BMWselectc; /GetBMWsgoingatleast100mph. varonlyFastBMWs=fromcinmyCars wherec.Make=BMW&c.Speed=100 selectc; 5、生成新的数据类型（投影）varmakesColors=fromcinmyCarsselectnewc.Make,c.Color; 6、Reverse()或者varsubset=(fromcinmyCarsselectc).Reverse(); foreach(Carcinsubset) Console.WriteLine(0isgoing1MPH,c.PetName,c.Speed); 7、排序默认是ascending/OrderallthecarsbyPetName. varsubset=fromcinmyCarsorderbyc.PetNameselectc; /Nowfindthecarsthataregoinglessthan55mph, /andorderbydescendingPetName subset=fromcinmyCars wherec.Speed55orderbyc.PetNamedescendingselectc; 默认顺序时也可以明确指明varsubset=fromcinmyCars orderbyc.PetNameascendingselectc; 8、Enumerable.Except()两个IEnumerable兼容的对象的差集1. staticvoidGetDiff() 2. 3. ListmyCars=newList 4. Yugo,Aztec,BMW; 5. ListyourCars=newList 6. BMW,Saab,Aztec; 7. varcarDiff=(fromcinmyCarsselectc) 8. .Except(fromc2inyourCarsselectc2); 9. Console.WriteLine(Hereiswhatyoudonthave,butIdo:); 10. foreach(stringsincarDiff) 11. Console.WriteLine(s);/PrintsYugo. 12. 以上介绍Linq基本语法一、LINQ查询符列表Query OperatorsMeaning in Lifefrom, inUsed to define the backbone for any LINQ expression, which allows you to extract a subset of data from a fitting container.whereUsed to define a restriction for which items to extract from a container.selectUsed to select a sequence from the container.join, on, equals, intoPerforms joins based on specified key. Remember, these “joins” do not need to have anything to do with data in a relational database.orderby, ascending, descendingAllows the resulting subset to be ordered in ascending or descending order.group, byYields a subset with data grouped by a specified value.另外还有一些没有操作符号，而是以扩展函数（泛型函数）的方式提供的函数：用不同方式产生结果集： Reverse(), ToArray(), ToList()集合操作： Distinct(), Union(), Intersect()统计函数： Count(), Sum(), Min(), Max()二、使用Enumerable获取Counts为了使用这些Enumerable扩展函数，一般把LINQ查询表达式用括号括起来，先转换为IEnumerable兼容的对象。staticvoidGetCount()stringcurrentVideoGames=Morrowind,BioShock,HalfLife2:Episode1,TheDarkness,Daxter,SystemShock2;/Gnumb=(fromgincurrentVideoGameswhereg.Length6orderbygselectg).Count();/numbisthevalue5.Console.WriteLine(0itemshonortheLINQquery.,numb);三、定义演示的实例classCarpublicstringPetName=string.Empty;publicstringColor=string.Empty;publicintSpeed;publicstringMake=string.Empty;publicoverridestringToString()returnstring.Format(Make=0,Color=1,Speed=2,PetName=3,Make,Color,Speed,PetName);staticvoidMain(stringargs)Console.WriteLine(*FunwithQueryExpressions*n);/ThisarraywillbethebasisofourtestingCarmyCars=newnewCarPetName=Henry,Color=Silver,Speed=100,Make=BMW,newCarPetName=Daisy,Color=Tan,Speed=90,Make=BMW,newCarPetName=Mary,Color=Black,Speed=55,Make=VW,newCarPetName=Clunker,Color=Rust,Speed=5,Make=Yugo,newCarPetName=Hank,Color=Tan,Speed=0,Make=Ford,newCarPetName=Sven,Color=White,Speed=90,Make=Ford,newCarPetName=Mary,Color=Black,Speed=55,Make=VW,newCarPetName=Zippy,Color=Yellow,Speed=55,Make=VW,newCarPetName=Melvin,Color=White,Speed=43,Make=Ford;/Wewillcallvariousmethodshere!Console.ReadLine();四、LINQ语法基本语法var result = from item in container orderby value ascending/descending select item;1、获取全部记录varallCars=fromcinmyCarsselectc;2、只获取字段名称varnames=fromcinmyCarsselectc.PetName;这里names就是隐式类型的变量。3、使用Enumerable.Distinct()varmakes=(fromcinmyCarsselectc.Make).Distinct();4、即可以在定义的时候调用Enumberalbe扩展函数varnames=fromcinmyCarsselectc.PetName;foreach(varninnames)Console.WriteLine(Name:0,n);也可以在兼容的数组类型上调用varmakes=fromcinmyCarsselectc.Make;Console.WriteLine(Distinctmakes:);foreach(varminmakes.Distinct()Console.WriteLine(Make:0,m);/NowgetonlytheBMWs.varonlyBMWs=fromcinmyCarswherec.Make=BMWselectc;/GetBMWsgoingatleast100mph.varonlyFastBMWs=fromcinmyCarswherec.Make=BMW&c.Speed=100selectc;5、生成新的数据类型（投影）varmakesColors=fromcinmyCarsselectnewc.Make,c.Color;6、Reverse()varsubset=(fromcinmyCarsselectc).Reverse();foreach (Car c in subset)Console.WriteLine(0 is going 1 MPH, c.PetName, c.Speed);或者varsubset=fromcinmyCarsselectc;foreach(Carcinsubset.Reverse()Console.WriteLine(c.ToString();7、排序默认是ascending/OrderallthecarsbyPetName.varsubset=fromcinmyCarsorderbyc.PetNameselectc;/Nowfindthecarsthataregoinglessthan55mph,/andorderbydescendingPetNamesubset=fromcinmyCarswherec.Speed55orderbyc.PetNamedescendingselectc;默认顺序时也可以明确指明varsubset=fromcinmyCarsorderbyc.PetNameascendingselectc;8、Enumerable.Except()两个IEnumerable兼容的对象的差集staticvoidGetDiff()ListmyCars=newListYugo,Aztec,BMW;ListyourCars=newListBMW,Saab,Aztec;varcarDiff=(fromcinmyCarsselectc).Except(fromc2inyourCarsselectc2);Console.WriteLine(Hereiswhatyoudonthave,butIdo:);foreach(stringsincarDiff)Console.WriteLine(s);/PrintsYugo.五、使用LINQ查询结果如果查询结果是强类型的，如string，List等，就可以不用var类型，而是使用合适的IEnumerable或IEnumerable（因为IEnumerable也扩展了IEnumerable）类型。classProgramstaticvoidMain(stringargs)Console.WriteLine(*LINQTransformations*n);IEnumerablesubset=GetStringSubset();foreach(stringiteminsubset)Console.WriteLine(item);Console.ReadLine();staticIEnumerableGetStringSubset()stringcurrentVideoGames=Morrowind,BioShock,HalfLife2:Episode1,TheDarkness,Daxter,SystemShock2;/NotesubsetisanIEnumerablecompatibleobject.IEnumerablesubset=fromgincurrentVideoGameswhereg.Length6orderbygselectg;returnsubset;只有该函数原型返回类型是IEnumerable，才可以使用var定义返回结果集类型。但是在投影操作中，由于结果集合类型是隐式的，在编译时才能确定，所以这里强制规定必须使用var/Error!Cantreturnavardatatype!staticvarGetProjectedSubset()CarmyCars=newCarnewCarPetName=Henry,Color=Silver,Speed=100,Make=BMW,newCarPetName=Daisy,Color=Tan,Speed=90,Make=BMW,newCarPetName=Mary,Color=Black,Speed=55,Make=VW,newCarPetName=Clunker,Color=Rust,Speed=5,Make=Yugo,newCarPetName=Melvin,Color=White,Speed=43,Make=Ford;varmakesColors=fromcinmyCarsselectnewc.Make,c.Color;returnmakesColors;/Nope!可以使用ToArray()把投影结果集转化为标志的CRL数组对象：/ReturnvalueisnowanArray.staticArrayGetProjectedSubset()CarmyCars=newCarnewCa