[英]Dynamic LINQ OrderBy + Method Count
我正在网页中显示一个对象公司表,我正在使用动态Linq OrderBy对每个属性进行排序。 我正在使用此代码https://stackoverflow.com/a/233505/265122
public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
{
return ApplyOrder<T>(source, property, "OrderBy");
}
public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
{
return ApplyOrder<T>(source, property, "OrderByDescending");
}
public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
{
return ApplyOrder<T>(source, property, "ThenBy");
}
public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
{
return ApplyOrder<T>(source, property, "ThenByDescending");
}
static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName) {
string[] props = property.Split('.');
Type type = typeof(T);
ParameterExpression arg = Expression.Parameter(type, "x");
Expression expr = arg;
foreach(string prop in props) {
// use reflection (not ComponentModel) to mirror LINQ
PropertyInfo pi = type.GetProperty(prop);
expr = Expression.Property(expr, pi);
type = pi.PropertyType;
}
Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
object result = typeof(Queryable).GetMethods().Single(
method => method.Name == methodName
&& method.IsGenericMethodDefinition
&& method.GetGenericArguments().Length == 2
&& method.GetParameters().Length == 2)
.MakeGenericMethod(typeof(T), type)
.Invoke(null, new object[] {source, lambda});
return (IOrderedQueryable<T>)result;
}
这很棒,但我也希望根据员工数量对公司进行分类。
像这样: query.OrderBy(“Employees.Count”)
到目前为止,我试图动态调用Count方法,但没有任何成功。
我修改了这样的代码:
foreach(string prop in props)
{
if (prop == "Count")
{
var countMethod = (typeof(Enumerable)).GetMethods().First(m => m.Name == "Count").MakeGenericMethod(type);
expr = Expression.Call(countMethod, expr);
break;
}
// Use reflection (not ComponentModel) to mirror LINQ.
PropertyInfo pi = type.GetProperty(prop);
expr = Expression.Property(expr, pi);
type = pi.PropertyType;
}
但我对expr = Expression.Call(countMethod, expr);
有一个例外expr = Expression.Call(countMethod, expr);
例外是:
ArgumentException
Expression of type 'System.Collections.Generic.ICollection`1[Employee]'
cannot be used for parameter of type
'System.Collections.Generic.IEnumerable`1[System.Collections.Generic.ICollection`1
[Employee]]' of method 'Int32 Count[ICollection`1]
System.Collections.Generic.IEnumerable`1[System.Collections.Generic.ICollection`1
Employee]])'
有关如何实现这一点的任何想法?
从你的要点下面我发现在这所证明一个简单的方法牛逼压扁在所有基本类型和接口的属性后 。
所以我实现了PropertyInfo的扩展方法,它将返回该类继承的所有接口和基类的所有属性。 问题是IList没有Count属性,但iCollection确实如此。 public static PropertyInfo[] GetPublicProperties(this Type type)
将展平所有属性,我们从那里得到正确的属性,这应该适用于任何属性,现在不仅仅是Count。
public class Program
{
private static IList<Company> _companies;
static void Main(string[] args)
{
var sort = "Employees.Count";
_companies = new List<Company>();
_companies.Add(new Company
{
Name = "c2",
Address = new Address {PostalCode = "456"},
Employees = new List<Employee> {new Employee(), new Employee()}
});
_companies.Add(new Company
{
Name = "c1",
Address = new Address {PostalCode = "123"},
Employees = new List<Employee> { new Employee(), new Employee(), new Employee() }
});
//display companies
_companies.AsQueryable().OrderBy(sort).ToList().ForEach(c => Console.WriteLine(c.Name));
Console.ReadLine();
}
}
public class Company
{
public string Name { get; set; }
public Address Address { get; set; }
public IList<Employee> Employees { get; set; }
}
public class Employee{}
public class Address
{
public string PostalCode { get; set; }
}
public static class OrderByString
{
public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
{
return ApplyOrder<T>(source, property, "OrderBy");
}
public static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
{
string[] props = property.Split('.');
Type type = typeof(T);
ParameterExpression arg = Expression.Parameter(type, "x");
Expression expr = arg;
foreach (string prop in props)
{
// use reflection (not ComponentModel) to mirror LINQ
PropertyInfo pi = type.GetPublicProperties().FirstOrDefault(c => c.Name == prop);
if (pi != null)
{
expr = Expression.Property(expr, pi);
type = pi.PropertyType;
}
else { throw new ArgumentNullException(); }
}
Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
object result = typeof(Queryable).GetMethods().Single(
method => method.Name == methodName
&& method.IsGenericMethodDefinition
&& method.GetGenericArguments().Length == 2
&& method.GetParameters().Length == 2)
.MakeGenericMethod(typeof(T), type)
.Invoke(null, new object[] { source, lambda });
return (IOrderedQueryable<T>)result;
}
public static PropertyInfo[] GetPublicProperties(this Type type)
{
if (type.IsInterface)
{
var propertyInfos = new List<PropertyInfo>();
var considered = new List<Type>();
var queue = new Queue<Type>();
considered.Add(type);
queue.Enqueue(type);
while (queue.Count > 0)
{
var subType = queue.Dequeue();
foreach (var subInterface in subType.GetInterfaces())
{
if (considered.Contains(subInterface)) continue;
considered.Add(subInterface);
queue.Enqueue(subInterface);
}
var typeProperties = subType.GetProperties(
BindingFlags.FlattenHierarchy
| BindingFlags.Public
| BindingFlags.Instance);
var newPropertyInfos = typeProperties
.Where(x => !propertyInfos.Contains(x));
propertyInfos.InsertRange(0, newPropertyInfos);
}
return propertyInfos.ToArray();
}
return type.GetProperties(BindingFlags.FlattenHierarchy
| BindingFlags.Public | BindingFlags.Instance);
}
}
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