Question

假设我有以下模型：

public class Department
{
    public ICollection<Employee> Employees { get; set; }
}

public class Employee
{
    public string Name { get; set; }
}

我想为此构建一个Expression：

departments.Where(x => x.Employees.Any(y => y.Name.Contains("foo")))

我有以下代码：

var departmentParameterExpression = Expression.Parameter(typeof(Department), "x");
PropertyExpression departmentListProperty = { x.Departments } // Value of the Expression shown in the debugger, actual code is some property helper to get the property by Name
var employeeParameterExpression = Expression.Parameter(typeof(Employee), "y");
PropertyExpression employeeNameProperty = { y.Name } // Same as departmenListProperty
var employeeNameContainsString = Expression.Call(employeeNameProperty, typeof(string).GetMethod("Contains"), Expression.Constant(token));
var compiledExpression = Expression.Lambda<Func<Employee, bool>>(employeeNameContainsString, employeeParameterExpression).Compile();

var anyMethod = typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public | BindingFlags.Instance).FirstOrDefault(x => x.Name == "Any" && x.GetParameters().Length == 2 &&  x.GetGenericArguments().Length == 1).MakeGenericMethod(typeof(Employee));

var containsEmployeeWithSearchString = Expression.Call(departmentListProperty, anyMethod, Expression.Constant(compiledExpression);

运行最后一行，会出现以下错误：

Static method requires null instance, non-static method requires non-null instance. Parameter name: instance

当我刚才.GetMethods(BindingFlags.Static)时，我不会得到任何Any() - 方法。

我如何使这项工作？

Answer 1

Any和Where是Enumerable上的扩展方法，因此根据定义为static。您尝试构建的实际表达式将等同于：

Enumerable.Where(departments, 
                 x => Enumerable.Any(x.Employees,
                                     y => y.Name.Contains("foo")
                                     )
                )

Answer 2

正如错误消息告诉您的那样，当您调用静态方法时，您无法为要调用的方法提供对象的实例;您需要为隐式参数提供null。

ICollection的表达式<t> .Any（Func <t，bool =“”>）

2 个答案: