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Lambda&Linq
var list = new List<Model> { new Model { Id = 1, UserName = "张三", Password = "123456", Email = "zhang3@yoy.com"}, new Model { Id = 2, UserName = "李四", Password = "234561", Email = "li4@yoy.com"}, new Model { Id = 3, UserName = "王五", Password = "345612", Email = "wang5@yoy.com"}, new Model { Id = 4, UserName = "赵六", Password = "456123", Email = "zhao6@yoy.com"}, }; //Add():添加单个,新加的数据将会在列表的最末端 //直译:添加 list.Add(new Model { Id = 5, UserName = "孙七", Password = "561234", Email = "sun7@yoy.com"}); //AddRange():添加多个,新加的数据将会在列表的最末端 //直译:范围添加 list.AddRange(new List<Model> { new Model { Id = 6, UserName = "刘一", Password = "612345", Email = "liu1@yoy.com"}, new Model { Id = 7, UserName = "陈二", Password = "654321", Email = "chen2@yoy.com"}, }); //Insert():添加单个,新加的数据将会在指定的索引位置,用法与Add()类似 //InsertRange():添加多个,新加的数据将会在指定的索引位置,AddRange()类似 //能指定位置插入数据,但是开销要大于Add/AddRange,目标集合越大,开销就越大 list.Insert(3, new Model { Id = 8, UserName = "周八", Password = "111111", Email = "zhou8@yoy.com" }); list.InsertRange(3, new List<Model> { new Model { Id = 9, UserName = "吴九", Password = "222222", Email = "wu9@yoy.com"}, new Model { Id = 10, UserName = "郑十", Password = "333333", Email = "zheng10@yoy.com"}, }); //将集合转化为指定的类型 var enumerable = list.AsEnumerable();//IEnumerable<T>类型 var queryable = list.AsQueryable();//IQueryable<T>类型 //IEnumerable类型内存迭代, //IQueryable类型表达式解析,语法树动态解析,延后查询 //AsQueryable()常用于存在不确定的查询条件之前 //Distinct():去重复,与sql中distinct相同,返回值为IEnumerable<T>类型 list = list.Distinct().ToList(); //ForEach():循环方法,括号中并非添加bool条件,而是进行操作 list.ForEach(f => f.Id += 1); list.ForEach(f => { if (f.Id == 7) f.Password = "1234567"; else f.Id -= 1; }); //Find():Find一类方法为Framework2.0时期的产物,现基本不用 var find = list.Find(f => f.Id == 1); var findAll = list.FindAll(f => f.Id == 1); //FirstOrDefault():第一个或者是默认值,返回值肯能为null //Framework3.5时期的产物,运用范围更广,支持IEnemerable<T>,但速度比Find较慢 //First():与FirstOrDefault()用法相似,但不会返回null,而抛出异常 var first = list.First(); var firstOrDefault = list.FirstOrDefault(); //最后一个,原理同First()/FirstOrDefault() var last = list.Last(); var lastOrDefault = list.LastOrDefault(); //唯一的一个,原理同First()/FirstOrDefault(),但如果出现重复数据,则抛异常 var single = list.Single(s => s.Id == 2); var singleOrDefault = list.SingleOrDefault(s => s.Id == 7); var newList = new List<NewModel> { new NewModel { UserId = 2, Address = "Address", CellPhone = "1383838438", Country = "中国"}, new NewModel { UserId = 3, Address = "Address", CellPhone = "1383838438", Country = "西班牙"}, new NewModel { UserId = 4, Address = "Address1", CellPhone = "1383838438", Country = "中国"}, new NewModel { UserId = 5, Address = "Address2", CellPhone = "1383838438", Country = "美国"}, }; //Join():关联,相当于sql中的inner join //写法:第一集合.Join(第二集合,第一的关联值,第二的关联值,(第一集合名,第二集合名)=>查询结果) //查询结果可自定义类型,返回值为IEnemerable<查询结果> var joinInfo = list.Join(newList, l => l.Id, nl => nl.UserId, (l, nl) => new { l, nl }).ToList(); var joinLinq = (from l in list join nl in newList on l.Id equals nl.UserId select new { l, nl }).ToList(); //GroupBy():按照指定参数进行分组,返回值类型为IEnemerable<IGrouping<string,T>> var groupInfo = newList.GroupBy(g => g.Country).ToList(); var groupLinq = (from nl in newList group nl by nl.Country into nlGroup select nlGroup); //GroupJoin():左关联,相当于sql中的left join后进行了一定的分组,等于主表.Join(子表.GroupBy()) //按照一定规律分组后进行关联,形成一对多的匿名类型,IEnemerable<{T1, IEnemerable<T2>}> //写法与Join相同:第一集合.GroupJoin(第二集合,第一的关联值,第二的关联值,(第一集合名,第二集合名)=>查询结果) //查询结果可自定义类型,返回值为IEnemerable<查询结果> //第一集合为主集合,第二集合为子集合,子集合条数可能为0 var groupJoin = list.GroupJoin(newList, l => l.Id, g => g.UserId, (l, g) => new { l, g }).ToList(); var groupJoinLinq = (from l in list join nl in newList on l.Id equals nl.UserId into g select new { l, g }).ToList(); //DefaultIfEmpty():查询默认或空实体,返回值为IEnumerable<T>类型,常用于做关联 var defaultList = list.DefaultIfEmpty().ToList(); //左关联变形:Join()/GroupJoin()加DefaultIfEmpty()方法实现 //先将两集合进行GroupJoin(),之后将查询结果中的子集合DefaultIfEmpty() //注:此处的做关联与sql中的左关联有所不同,此处的左关联为一对一或一对null var leftJoin = list.GroupJoin(newList, l => l.Id, g => g.UserId, (l, g) => new { l, g = g.DefaultIfEmpty() }).ToList(); var leftLinq1 = (from l in list join nl in newList on l.Id equals nl.UserId into g select new { l, g = g.DefaultIfEmpty() }); var leftLinq2 = (from l in list join nl in newList on l.Id equals nl.UserId into nlJoin from g in nlJoin.DefaultIfEmpty() select new { l, g }); //All():集合中的数据是否全部符合条件 //直译:全部 var trueAll = list.All(a => a.Id > 0); var falseAll = list.All(a => a.Id > 1); //Any():集合中是否含有符合条件的数据 //直译:存在 var trueAny = list.Any(a => a.Id == 7); var falseAny = list.Any(a => a.Id == 11); //Min()/Max():最小值/最大值 //筛选出指定值/指定算法为最小/最大的数据,返回单条 //可与左关联/排序等活用 var minList = list.Min(m => m.Id); var maxList = list.Max(m => m.Email.Length); //OrderBy()/OrderByDescending():正序/逆序 //按照指定字段/指定算法进行正序/逆序的排序 //可与左关联、分页等活用 var orderBy = list.OrderBy(o => o.Id).ToList(); var orderByLinq = (from l in list orderby l.Id select l).ToList(); var orderByDesc = list.OrderByDescending(o => o.Email.Length); var orderByDescLinq = (from l in list orderby l.Email.Length descending select l).ToList(); //Reverse():反转排序,List无法适用 var reverse = list.Where(w => true).Reverse().ToList(); //Select():将一个实体中的数据转为另一个实体 //返回值类型为:IEnumerable<T> var select1 = list.Select(s => s.Id).ToList();//指定字段/值 var select2 = list.Select(s => new { s.UserName, UserEmail = s.Email }).ToList();//匿名类型 var select3 = list.Select(s => new UserInfo { UserId = s.Id, UserName = s.UserName, UserEmail = s.Email }).ToList(); var select1Linq = (from l in list select l.Id).ToList(); var select2Linq = (from l in list select new { l.UserName, UserEmail = l.Email }).ToList(); var select3Linq = (from l in list select new UserInfo { UserId = l.Id, UserName = l.UserName, UserEmail = l.Email }).ToList(); //SelectMany():查询出指定实体中的指定子集 var selectMany = groupJoin.SelectMany(s => s.g).ToList(); var country1 = groupJoin.SelectMany(s => s.g).Select(s => s.Country).ToList(); var country2 = groupJoin.Select(s => s.g.Select(ss => ss.Country)).ToList(); //Skip():跳过指定个数,常用于分页等 var skip = select1.Skip(1); //Take():获取指定个数,常用于分页等 var take = select1.Take(1); //SkipWhile():跳过值,直到符合条件为止,按序跳过,当符合条件开始获取剩余的 //直译:跳过直到 var skipWhile1 = select1.SkipWhile(w => w < 9).ToList(); var skipWhile2 = select1.SkipWhile(w => w == 1).ToList(); //TakeWhile():获取值,直到符合条件为止,按序获取,从第一条获取,当不符合条件则跳出 //直译:获取直到 var takeWhile1 = select1.TakeWhile(w => w < 10).ToList(); var takeWhile2 = select1.TakeWhile(w => w == 1).ToList(); //Sum():求和,指定值的和,与sql中的功能相同 var sum = list.Sum(s => s.Id); //Union():追加数据,与sql中的功能相同 var doubleList = select1.Union(skip).ToList(); //Where():查询条件,与sql中的功能相同 var where = select1.Where(w => w > 5).ToList(); ; //删除指定数据 //Remove():删除指定数据,参数为数据类型 //RemoveAt():删除指定索引位置的数据 //RemoveRange():批量删除指定索引位置的数据(索引位置, 删除个数) //RemoveAll():删除全部符合条件的数据 list.Remove(firstOrDefault); list.RemoveAt(2); list.RemoveRange(3, 2); list.RemoveAll(r => r.Id > 4); var test = from l in list join nl in newList on l.Id equals nl.UserId let x = l.Password select new { x, nl }; Console.ReadKey();
Lambda&Linq
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