C#执行表达式树(Expression Tree)的具体使用

Expression<Func<int, int, int>> add = (x, y) => x + y;

// 创建参数表达式
ParameterExpression left = Expression.Parameter(typeof(int), "left");
ParameterExpression right = Expression.Parameter(typeof(int), "right");

// 创建加法表达式
BinaryExpression sum = Expression.Add(left, right);

// 创建参数表达式
ParameterExpression input = Expression.Parameter(typeof(int), "input");

// 创建平方表达式
UnaryExpression square = Expression.Power(input, Expression.Constant(2));

var left = Expression.Constant(3);
var right = Expression.Constant(4);
var multiplication = Expression.Multiply(left, right);

var originalExpression = Expression.Multiply(left, right);
var modifiedExpression = originalExpression.Update(left, Expression.Constant(5));

var parent = originalExpression.RemoveNode(originalExpression.Body);

void Visit(Expression node)
{
    if (node is BinaryExpression binary)
    {
        Visit(binary.Left);
        Visit(binary.Right);
    }
    else if (node is UnaryExpression unary)
    {
        Visit(unary.Operand);
    }
    else if (node is ConstantExpression constant)
    {
        Console.WriteLine($"常量值：{constant.Value}");
    }
    // ... 其他节点类型的处理逻辑
}

void DfsTraversal(Expression node)
{
    if (node == null)
        return;
    Console.WriteLine($"节点类型：{node.NodeType}");
    if (node is BinaryExpression binary)
	{
	    DfsTraversal(binary.Left);
	    DfsTraversal(binary.Right);
	}
	else if (node is UnaryExpression unary)
		{
		    DfsTraversal(unary.Operand);
		}
		// ... 其他节点类型的处理逻辑
	}

var xml = @"<root><person id='1'><name>张三</name><age>30</age></person><person id='2'><name>李四</name><age>40</age></person></root>";
var xmlDocument = new XmlDocument();
xmlDocument.LoadXml(xml);
var expression = Expression.ParseLambda<Func<XmlNode, bool>>(
    @"param => param.Name == 'name' && param.Attributes['id'].Value == '1'",
    typeof(XmlNode));
var query = xmlDocument.XPathSelectNodes(expression);

var json = @"{'name': '张三', 'age': 30, 'city': '北京'}";
var jsonDocument = JsonDocument.Parse(json);
var expression = Expression.ParseLambda<Func<JsonElement, bool>>(
    @"param => param.Value<string>(""name"") == ""张三"" && param.Value<int>(""age"") == 30",
    typeof(JsonElement));
var query = jsonDocument.RootElement.EnumerateArray().Where(expression).ToArray();