//方式一//分成key-value的数组string[] id = list.Select(a =>a.id.ToString()).ToArray();//dt是datatable类型的,执行LINQ语句,这里的.AsEnumerable()是延迟发生,不会立即执行,实际上什么都没有发生string[] id = dt.AsEnumerable().Select(a => a.Field<int>("id").ToString()).ToArray();/...
Array' does not contain a definition for 'Select' and no extension method 'Select' accepting a first argument of type 'System.Array' could be found (are you missing a using directive or an assembly reference?) C# Console App - Can't retrieve SOAP 1.2 response from Web Service C# Console...
string ids = ",2,3,4,5,"; var list = context.TestTables.Where(a => ids.Contains(a.IDSearched)).ToList(); 上面语句运行时,LINQ To Entities会将其翻译为如下SQL语句: SELECT [Extent1].[RID] AS [RID], [Extent1].[NAME] AS [NAME], [Extent1].[ROWDATE] AS [ROWDATE], [Extent1]...
() where c.active select c).ToList();/*C#写法3*/IEnumerable JointList = ( from r1 in list...( inner: salaryList, /*因为比较器用到了name和occupation两个属性,所以这里的Selector要包含这两个有用的属性值...在数据库或其他数据源操作中,Join操作使得从多个表中组合数据变得可能,极...
varlist=newArrayList{3,8,1,6,5,4,7,2,9};varselection=fromeinlistselecte+1; 但是,这样书写有一个问题。ArrayList类型是很早的数据类型,它虽然是一个集合,但里面的元素是object类型的,虽然我们知道,我们这个集合里只存int元素,但因为它自身只实现了IEnumerable接口,而没有实现泛型的版本(它自己在没有泛型之...
代码语言:dotnet 复制 /*同样需要上面求交集时的比较对象*//*查询年龄大于25的用户集合,投影存储他们的姓名和职业*/List<User>user_list=list.Where(u=>u.age>25).Select(g=>newUser(){name=g.name
List<int> numbers = [1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]; IEnumerable<int> queryFactorsOfFour = from num in numbers where num % 4 == 0 select num; // Store the results in a new variable // without executing a foreach loop. var factorsofFourList = queryFactorsOfFour...
Population > 10000 select city; List<City> largeCitiesList2 = largeCitiesQuery.ToList(); 查询表达式可能会包含多个from子句。在源序列中的每个元素本身就是集合或包含集合时,可以使用其它from子句。如下示例所示,假设具有County对象的集合,每个对象都包含名为Cities的City对象集合,若要查询每个County中的City对象...
{88, 94, 65, 91}} Dim arrList As New ArrayList() arrList.Add(student1) arrList.Add(student2) arrList.Add(student3) arrList.Add(student4) ' Use an explicit type for non-generic collections Dim query = From student As Student In arrList Where student.Scores(0) > ...
List<int> numQuery2 = (fromnuminnumberswhere(num %2)==0selectnum).ToList();// or like this:// numQuery3 is still an int[]varnumQuery3 = (fromnuminnumberswhere(num %2)==0selectnum).ToArray(); 此外,还可以通过在紧跟查询表达式之后的位置放置一个foreach循环来强制执行查询。 但是,通过...