c# - 网络核心 : Find Data Type for any Variable Field in Class

Question

我如何获取这个 OrderBy 表达式树并使其接受任何订单类型、int、float、string、boolean 等？是否可以？现在它的类型转换为仅字符串。我应该在调用方法时将所有内容都转换为字符串，还是有更好的方法使它更通用？

我只需要类 T 中这个 propertyName 的数据类型，所以我可以放在下面的函数中。测试这些，还没有运气。

成员(member)类型,获取类型(),字段类型

OrderBy Expression Tree in Net Core Linq for Extension Method

创建表达式:

public static class ExpressionTreesExtesion
{
    public static Expression<Func<T,string>> OrderByExpression<T>(this IEnumerable<T> enumerable, string propertyName)
    {
        var propInfo = typeof(T).GetProperty(propertyName);

        var collectionType = typeof(T);

        var parameterExpression = Expression.Parameter(collectionType, "x");
        var propertyAccess = Expression.MakeMemberAccess(parameterExpression, propInfo);
        var orderExpression = Expression.Lambda<Func<T,string>>(propertyAccess, parameterExpression);
        return orderExpression;
    }
}

如何调用:

var ProductExpression = records.OrderByExpression("Name");

var result  = records.OrderBy(ProductExpression.Compile());
ProductExpression.Compile() above will compile into x => x.Name, where column name is supplied at the run-time

Answer 1

因为类型在编译时是未知的，你将不能使用像Expression<Func<T,TKey>>这样的强类型返回类型。 .

public static class ExpressionTreesExtension {
    static readonly Type funcTTResult = typeof(Func<,>);
    public static IOrderedQueryable<T> OrderByProperty<T>(this IEnumerable<T> enumerable, string propertyName) {
        var itemType = typeof(T);
        var propertyInfo = itemType.GetProperty(propertyName);
        var propertyType = propertyInfo.PropertyType;
        // Func<T,TPropertyType>
        var delegateType = funcTTResult.MakeGenericType(itemType, propertyType);
        // T x =>
        var parameterExpression = Expression.Parameter(itemType, "x");
        // T x => x.Property
        var propertyAccess = Expression.Property(parameterExpression, propertyInfo);
        // Func<T,TPropertyType> = T x => x.Property
        var keySelector = Expression.Lambda(delegateType, propertyAccess, parameterExpression);

        var query = enumerable.AsQueryable();

        // query.OrderBy(x => x.Property)
        MethodCallExpression orderByExpression = Expression.Call(
             typeof(Queryable),
             "OrderBy",
             new[] { query.ElementType, propertyInfo.PropertyType },
             query.Expression, keySelector);

        // Create an executable query from the expression tree. 
        return (IOrderedQueryable<T>)query.Provider.CreateQuery<T>(orderByExpression);
    }
}

引用 How to: Use Expression Trees to Build Dynamic Queries (C#)

像这样使用

//IEnumerable<Person> records...
var data = records.OrderByProperty("Name");