为类的所有属性构建表达式

Question

使用Expression的经验并不多，而且很难理解更大的情况。

我有一个类，它定义了大量属性。我尝试使用反射/表达式来计算这些属性，而不是做很多愚蠢的类型的工作。

这门课的一个简短的样本：

[Function(Name = "sensors")]
internal class Sensors
{
    [CabinetDoubleSensor(SensorType = SensorType.Temperature, Precision = 3)]
    [JsonProperty(PropertyName = "IO_PCW_FL_SPR")]
    public JsonSensor<double> IOPcwFlSpr { get; set; } = new JsonSensor<double>();

    [CabinetDoubleSensor(SensorType = SensorType.Temperature, Precision = 3)]
    [JsonProperty(PropertyName = "IO_PCW_RL_SPR")]
    public JsonSensor<double> IOPcwRlSpr { get; set; } = new JsonSensor<double>();

    // 100+ sensor definitions below
}

我希望评估所有属性，并将它们存储在一个列表中，如下所示：

    public IEnumerable<ISensor> UpdateSensors(Json.Sensors jsonUpdate)
    {
        // To test if it works, but clearly, I do NOT want to list all sensor evaluations here!
        UpdateSensor(() => jsonUpdate.IOPcwFlSpr);

        return SensorMap.Values.ToList();
    }

    private void UpdateSensor(Expression<Func<JsonSensor<double>>> propertySelector)
    {
        if (propertySelector.Body is MemberExpression expression)
        {
            var compiledExpression = propertySelector.Compile();
            var jsonSensor = compiledExpression.Invoke();

            var name = expression.Member.Name;
            var cabinetSensor = SensorMap[name];
            cabinetSensor.Value = jsonSensor.Value.ToString($"F{cabinetSensor.Precision}");
        }
    }

所以我被困的那部分。如前所述，我不想打电话给UpdateSensor(() => jsonUpdate.SensorName 100+ times。所以我想找一种方法自己来构造lambda表达式。

    private static readonly List<PropertyInfo> Properties;

    static SensorFactory()
    {
        Properties = typeof(Json.Sensors).GetProperties().ToList();
    }

    public IEnumerable<ISensor> Test(Json.Sensors jsonUpdate)
    {
        foreach (var property in Properties)
        {
            var getterMethodInfo = property.GetGetMethod();
            var parameterExpression = Expression.Parameter(jsonUpdate.GetType());
            var getterCall = Expression.Call(parameterExpression, getterMethodInfo);

            UnaryExpression castToObject = Expression.Convert(getterCall, typeof(JsonSensor<double>));
            var lambda = (Expression<Func<JsonSensor<double>>>)Expression.Lambda(castToObject, parameterExpression);

            UpdateSensor(lambda);
        }

        // not relevant
        return null;
    }

该演员是非法的：

'System.Linq.Expressions.Expression1[System.Func2[Asml.Mbi.FlowAndTemperature.Peripherals.Cabinet.Json.Sensors，Asml.Mbi.FlowAndTemperature.Peripherals.Cabinet.Json.JsonSensor1[System.Double]]]' to type 'System.Linq.Expressions.Expression1[System.Func1[Asml.Mbi.FlowAndTemperature.Peripherals.Cabinet.Json.JsonSensor1System.Double]]'.‘：’无法转换类型为System.InvalidCastException的对象

我想(/hope)我已经接近了，但我不知道如何将Expression<Func<JsonSensor<double>>>作为返回值。

Answer 1

实际上，您的代码中很少有问题。

异常本身被抛出，因为您向Lambda方法提供了一个参数，这样它将生成Func<T1, T2>。Func<T>不接受任何参数，所以应该调用Expression.Lambda(castToObject)。

无论如何，您可能应该将其更改为Func<Sensors, JsonSensor<double>>，否则需要在lambda中将jsonUpdate包装为常量。

下面是调整后的UpdateSensor和Test方法的示例：

private static void UpdateSensor(Sensors jsonUpdate, Expression<Func<Sensors, JsonSensor<double>>> propertySelector)
{
    if (propertySelector.Body is MemberExpression expression)
    {
        var compiledExpression = propertySelector.Compile();
        // Signature was changed and jsonUpdate is not compiled into lambda; we need to pass reference
        var jsonSensor = compiledExpression.Invoke(jsonUpdate);

        var name = expression.Member.Name;
        var cabinetSensor = SensorMap[name];
        cabinetSensor.Value = jsonSensor.Value.ToString($"F{cabinetSensor.Precision}");
    }
}

public IEnumerable<Sensor> Test(Sensors jsonUpdate)
{
    foreach (var property in Properties)
    {
        var parameterExpression = Expression.Parameter(jsonUpdate.GetType());
        // You don't need call or GetMethod, you need to access Property
        var propertyCall = Expression.Property(parameterExpression, property);

        // Cast is redundant, and if you add it UpdateSensor will do nothing
        // UnaryExpression castToObject = Expression.Convert(propertyCall, typeof(JsonSensor<double>));
        var lambda = Expression.Lambda<Func<Sensors, JsonSensor<double>>>(propertyCall, parameterExpression);

        UpdateSensor(jsonUpdate, lambda);
    }

    // not relevant
    return null;
}