c# - 从对象创建动态 Func

Question

我有一个条件对象，如果它的值不为空，我将在其中将每个属性转换为一个函数。

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

这是我目前所拥有的，但我很确定我没有正确定义 lambda。这就是我想要实现的目标。 funcs.Add(x => x.ColumnA == criteria.ColumnA)。

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，它只是不工作。

如果您能提供任何帮助，我们将不胜感激。

Answer 1

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;
    }

示例实体和示例标准:

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)));

此代码使用强类型成员访问，而不是您的动态代码，因此，您可以缓存每对“实体 - 条件”的条件列表，并更快地形成匹配的测试实例。