C# LINQ group by属性作为参数
我有一个要使用LINQ查询的对象列表。我希望能够按属性对它们进行分组C# LINQ group by属性作为参数,c#,linq,C#,Linq,我有一个要使用LINQ查询的对象列表。我希望能够按属性对它们进行分组 var query = from item in expense orderby item.ExpenseTime descending group item by item.Location; var query = from item in expense orderby item.ExpenseTime descending group item by item.ExpenseType;
var query = from item in expense
orderby item.ExpenseTime descending
group item by item.Location;
var query = from item in expense
orderby item.ExpenseTime descending
group item by item.ExpenseType;
var query = from item in expense
orderby item.ExpenseTime descending
group item by item.Person;
有没有办法将属性指定为方法的参数
public static void GetExpensesBy(List<Expense> expense, Property myGroupingProperty)
{
var query = from item in expense
orderby item.ExpenseTime descending
group item by item.myGroupingProperty;
// ....
}
public static void GetExpensesBy(列出费用,属性myGroupingProperty)
{
var查询=来自费用中的项目
orderby item.ExpenseTime降序
按项分组。myGroupingProperty;
// ....
}
请注意,在查询之后,有一些代码是通用的,与组无关。Microsoft编写了一个动态Linq库 此库允许您动态指定任何Linq查询
公共静态void GetExpensesBy(列表费用、表达式groupbyExpression)
public static void GetExpensesBy<T>(List<Expense> expense, Expression<Func<A,T>> groupbyExpression)
{
var query = from item in expense
orderby item.ExpenseTime descending;
query.GroupBy(groupbyExpression);
// ....
}
{
var查询=来自费用中的项目
orderby item.ExpenseTime降序;
GroupBy(groupbyExpression);
// ....
}
并创造出这样的表达方式
Expression<Func<Expense, string>> group = (q) => q.Location;
expressiongroup=(q)=>q.位置;
如果您修改GetExpenseBy
如下
public static void GetExpensesBy<TKey>(List<Expense> expense,
Func<Expense, TKey> myGroupingProperty)
{
var query = (from item in expense
orderby item.ExpenseTime descending
select item).GroupBy(myGroupingProperty);
// ....
}
为什么要使用表达式?我可以在同一个表达式中创建多个GroupBy吗?示例:按位置分组,然后按同一表达式中的人分组?比如GetExpensesBy(费用,项目=>item.Location,项目=>item.Person);如果需要按人员和地点分组,可以使用
GetExpensesBy(expense,item=>new{item.location,item.person})代码>如何将其转换为字典TKey将包含什么?由于函数是一个不返回任何内容的空函数,如何从函数中获取新创建的集合?
GetExpensesBy(expense, item => item.Location);
GetExpensesBy(expense, item => item.Person);
GetExpensesBy(expense, item => item.ExpenseType);