Linq：使用表达式树语法按多列分组

我想更改以下代码，以便处理超过1个属性的分组

private Expression<Func> DynamicGroupBy(string propertyName) { var parameterExp = Expression.Parameter(typeof(ProfileResultView), "x"); var memberExp = Expression.PropertyOrField(parameterExp, propertyName); return Expression.Lambda<Func>(memberExp, parameterExp); } 

所以这将被翻译成

 GroupBy(x => new { x.Column1, x.Column2 }) 

如何在表达式树语法中编写匿名类型？

Answer 1

如果分组键的类型对您无关紧要，您可以动态创建类型并根据这些类型调用分组：

 public static Expression> DynamicGroupBy (params string[] properties) { var entityType = typeof(TSource); var props = properties.Select(x => entityType.GetProperty(x)).ToList(); var source = Expression.Parameter(entityType, "x"); // create x=> new myType{ prop1 = x.prop1,...} var newType = CreateNewType(props); var binding = props.Select(p => Expression.Bind(newType.GetField(p.Name), Expression.Property(source, p.Name))).ToList(); var body = Expression.MemberInit(Expression.New(newType), binding); var selector = Expression.Lambda>(body, source); return selector; } public static Type CreateNewType(List props) { AssemblyName asmName = new AssemblyName("MyAsm"); AssemblyBuilder dynamicAssembly = AssemblyBuilder .DefineDynamicAssembly(asmName, AssemblyBuilderAccess.Run); ModuleBuilder dynamicModule = dynamicAssembly.DefineDynamicModule("MyAsm"); TypeBuilder dynamicAnonymousType = dynamicModule .DefineType("MyType", TypeAttributes.Public); foreach (var p in props) { dynamicAnonymousType.DefineField(p.Name, p.PropertyType, FieldAttributes.Public); } return dynamicAnonymousType.CreateType(); } 

请注意，组密钥类型是object 。