集合上的表达式树 'Any'

Question

我正在尝试确定集合中的任何对象是否将目标属性设置为 true。我怎样才能做到这一点？这是我目前所拥有的：

public class AnyValidAttribute : ValidationAttribute
{
    private static MethodInfo AnyMethod =
        typeof(Enumerable)
          .GetMethods()
          .First(m => m.Name == "Any" && m.GetParameters().Length == 2));

    string booleanPropertyToCheck;
    Type entityType;

    public AnyValidAttribute(string booleanPropertyToCheck, Type entityType)
    {
        this.booleanPropertyToCheck = booleanPropertyToCheck;
        this.entityType = entityType;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var collection = new List<object>((IEnumerable<object>)value);
        var propInfo = this.entityType.GetProperty(this.booleanPropertyToCheck);
        var param = Expression.Parameter(this.entityType, "entity");
        var property = Expression.MakeMemberAccess(param, propInfo);
        var trueValue = Expression.Constant(true);
        var comparison = Expression.Equal(property, trueValue);
        var lambda = Expression.Lambda(comparison, param);
        var call = Expression.Call(AnyMethod, comparison, lambda);
        var anyTrue = ???

        return true ? null : new ValidationResult("At least one is required.");
    }
}

Answer 1

您想动态调用Any方法吗？

我建议这样做：

var anyDelegate = lambda.Compile();
var genericMethod = AnyMethod.MakeGenericMethod(entityType);
var anyTrue = (bool)genericMethod.Invoke(null, new[] {value, genericMethod});

你真的不需要你的 Call 表达式。

在你的方法中完成调用就像（在 Linqpad 中对我有用）：

var propInfo = this.entityType.GetProperty(this.booleanPropertyToCheck);

var param = Expression.Parameter(this.entityType, "entity");
var property = Expression.MakeMemberAccess(param, propInfo);
var trueValue = Expression.Constant(true);
var comparison = Expression.Equal(property, trueValue);
var lambda = Expression.Lambda(comparison, param);  

var anyDelegate = lambda.Compile();

var genericMethod = AnyMethod.MakeGenericMethod(entityType);
var anyTrue = (bool)genericMethod.Invoke(null, new[] { value, anyDelegate });

集合上的表达式树 'Any'

Expression Tree 'Any' on Collection

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