C# 思维弯曲器 : Compile string to assignment expression at runtime

Question

假设我有以下 C# 代码:

//build an object
var mynewObj = new Thing();

//build an assignment value
var val = "abc";

var memberExpression = "x.PropertyX.Id = y";

[? some stuff happens ?]

Assert.IsTrue(myNewObj.PropertyX.Id == "abc");

memberExpression 是某些数据库中的一个值。我想获取这些片段，构建一个表达式，然后编译/执行它。我需要每秒执行此操作约 30 次，持续数小时，因此它必须快速且占用内存少。

Answer 1

最好的办法是使用表达式来构建一个 Action ，编译并缓存它。下面是一个稍微简化的示例，说明如何执行此操作。在这种情况下，我只在属性图中深入一层。

    /// <summary>
    /// Build a lambda expression for a setter
    /// </summary>
    public static Action<T, U> GetSetter<T, U>(string propertyName)
    {
        // TODO: Maintain a dictionary mapping typeof(T)+property onto the 
        // resulting Action so this can be cached

        PropertyInfo property = typeof(T).GetProperty(propertyName);
        var setMethod = property.GetSetMethod();

        var parameterT = Expression.Parameter(typeof(T), "x");
        var parameterU = Expression.Parameter(typeof(U), "y");

        var newExpression =
            Expression.Lambda<Action<T, U>>(
                Expression.Call(parameterT, setMethod, parameterU),
                parameterT,
                parameterU
            );

        return newExpression.Compile();
    }

使用它:-

        //build an object
        var mynewObj = new Thing();

        //build an assignment value
        var val = "abc";

        var propertyName = "PropertyX";
        var setter = GetSetter<Thing, string>(propertyName);

        // Execute the cached setter (it's really fast!)
        setter(mynewObj, val);

        Debug.Assert(mynewObj.PropertyX == "abc") ;