创建动态函数<；T、 TResult>；来自对象

本文关键字：gt 对象 TResult 动态 函数 lt 创建 | 更新日期: 2023-09-27 18:23:56

我有一个criteria对象，如果它的值不为null，我将在其中将每个属性转换为func。

public class TestClassCriteria
{
    public bool? ColumnA { get; set; }
    public bool? ColumnB { get; set; }
}

这就是我到目前为止所做的，但我很确定我没有正确定义lambda。这就是我努力实现的目标。CCD_ 1。

var properties = criteria.GetType().GetProperties();
var funcs = new List<Func<dynamic, bool>>();
foreach (var property in properties)
{
    var propertyName = property.Name;
    funcs.Add(x => x.GetType().GetProperty(propertyName).Name == criteria.GetType().GetProperty(propertyName).Name);
}

它没有崩溃或导致任何错误，只是不起作用。

如能提供任何帮助，我们将不胜感激。

创建动态函数<；T、 TResult>；来自对象

你想要这样的东西吗？

    static List<Func<TEntity, TCriteria, bool>> GetCriteriaFunctions<TEntity, TCriteria>()
    {
        var criteriaFunctions = new List<Func<TEntity, TCriteria, bool>>();
        // searching for nullable properties of criteria
        var criteriaProperties = typeof(TCriteria)
            .GetProperties()
            .Where(p => p.PropertyType.IsGenericType && p.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>));
        foreach (var property in criteriaProperties)
        {
            // this is entity parameter
            var entityParameterExpression = Expression.Parameter(typeof(TEntity));
            // this is criteria parameter
            var criteriaParameterExpression = Expression.Parameter(typeof(TCriteria));
            // this is criteria property access: "criteria.SomeProperty"
            var criteriaPropertyExpression = Expression.Property(criteriaParameterExpression, property);
            // this is testing for equality between criteria property and entity property;
            // note, that criteria property should be converted first;
            // also, this code makes assumption, that entity and criteria properties have the same names
            var testingForEqualityExpression = Expression.Equal(
                Expression.Convert(criteriaPropertyExpression, property.PropertyType.GetGenericArguments()[0]), 
                Expression.Property(entityParameterExpression, property.Name));
            // criteria.SomeProperty == null ? true : ((EntityPropertyType)criteria.SomeProperty == entity.SomeProperty)
            var body = Expression.Condition(
                Expression.Equal(criteriaPropertyExpression, Expression.Constant(null)), 
                Expression.Constant(true),
                testingForEqualityExpression);
            // let's compile lambda to method
            var criteriaFunction = Expression.Lambda<Func<TEntity, TCriteria, bool>>(body, entityParameterExpression, criteriaParameterExpression).Compile();
            criteriaFunctions.Add(criteriaFunction);
        }
        return criteriaFunctions;
    }

样本实体和样本标准：

class CustomerCriteria
{
    public int? Age { get; set; }
    public bool? IsNew { get; set; }
}
class Customer
{
    public string Name { get; set; }
    public int Age { get; set; }
    public bool IsNew { get; set; }
}

用法：

        var criteriaFunctions = GetCriteriaFunctions<Customer, CustomerCriteria>();
        var customer1 = new Customer { Name = "John", Age = 35, IsNew = false };
        var customer2 = new Customer { Name = "Mary", Age = 27, IsNew = true };
        var criteria1 = new CustomerCriteria { Age = 35 };
        var criteria2 = new CustomerCriteria { IsNew = true };
        Console.WriteLine("Is match: {0}", criteriaFunctions.All(f => f(customer1, criteria1)));
        Console.WriteLine("Is match: {0}", criteriaFunctions.All(f => f(customer2, criteria1)));
        Console.WriteLine("Is match: {0}", criteriaFunctions.All(f => f(customer1, criteria2)));
        Console.WriteLine("Is match: {0}", criteriaFunctions.All(f => f(customer2, criteria2)));

该代码使用强类型成员访问，而不是动态代码，因此，您可以更快地缓存每对"实体-标准"的标准列表和测试实例表单匹配。

您当前的表达式正在比较属性名称，但我认为您希望比较属性值：

var funcs = new List<Func<dynamic, bool>>();
foreach (var property in criteria.GetType().GetProperties())
{
    funcs.Add(x => x.GetType().GetProperty(property.Name).GetValue(x, null) == property.GetValue(criteria, null));
}

但是，你确定你需要这样做吗？可能有一种更好的方法来重构代码，这样您就不需要使用反射来比较两个不相关对象上碰巧具有相同名称的属性。

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