将 Expression<Func<T, T>>转成实体T
public class MyEntity
{public int Age { get; set; }public string Name { get; set; }
} public static class ExpressionExtension{#region 表达式类型字典/// <summary>/// 表达式类型字典/// </summary>private static readonly Dictionary<ExpressionType, string> NodeTypeDic = new Dictionary<ExpressionType, string>{{ExpressionType.AndAlso," AND "},{ExpressionType.OrElse," OR "},{ExpressionType.Equal," = "},{ExpressionType.NotEqual," != "},{ExpressionType.LessThan," < "},{ExpressionType.LessThanOrEqual," <= "},{ExpressionType.GreaterThan," > "},{ExpressionType.GreaterThanOrEqual," >= "}};#endregion#region 获取表达式类型转换结果/// <summary>/// 获取表达式类型转换结果/// </summary>/// <param name="node">二元表达式</param>/// <returns></returns>public static string GetExpressionType(this BinaryExpression node){var nodeTypeDic = NodeTypeDic[node.NodeType];string nodeType = null;if (node.Right.NodeType == ExpressionType.Constant && ((ConstantExpression)node.Right).Value == null){switch (node.NodeType){case ExpressionType.Equal:nodeType = " IS ";break;case ExpressionType.NotEqual:nodeType = " IS NOT ";break;}}return !string.IsNullOrEmpty(nodeType) ? nodeType : nodeTypeDic;}#endregion#region 获取最底层成员表达式/// <summary>/// 获取最底层成员表达式/// </summary>/// <param name="e"></param>/// <returns></returns>public static MemberExpression GetRootMember(this MemberExpression e){if (e.Expression == null || e.Expression.NodeType == ExpressionType.Constant)return e;return e.Expression.NodeType == ExpressionType.MemberAccess? ((MemberExpression)e.Expression).GetRootMember(): null;}#endregion#region 转换成一元表达式并取值/// <summary>/// 转换成一元表达式并取值/// </summary>/// <param name="expression"></param>/// <returns></returns>public static object ToConvertAndGetValue(this Expression expression){if (expression.Type != typeof(object))expression = Expression.Convert(expression, typeof(object));var lambdaExpression = Expression.Lambda<Func<object>>(expression);return lambdaExpression.Compile().Invoke();}#endregionpublic static object MemberToValue(this MemberExpression memberExpression){var topMember = GetRootMember(memberExpression);if (topMember == null)throw new InvalidOperationException("需计算的条件表达式只支持由 MemberExpression 和 ConstantExpression 组成的表达式");return memberExpression.MemberToValue(topMember);}public static object MemberToValue(this MemberExpression memberExpression, MemberExpression topMember){if (topMember.Expression == null){//var aquire = Cache.GetOrAdd(memberExpression.ToString(), key => GetStaticProperty(memberExpression));var aquire = GetStaticProperty(memberExpression);return aquire(null, null);}else{//var aquire = Cache.GetOrAdd(memberExpression.ToString(), key => GetInstanceProperty(memberExpression, topMember));var aquire = GetInstanceProperty(memberExpression, topMember);return aquire((topMember.Expression as ConstantExpression).Value, null);}}private static Func<object, object[], object> GetInstanceProperty(Expression e, MemberExpression topMember){var parameter = Expression.Parameter(typeof(object), "local");var parameters = Expression.Parameter(typeof(object[]), "args");var castExpression = Expression.Convert(parameter, topMember.Member.DeclaringType);var localExpression = topMember.Update(castExpression);var replaceExpression = ExpressionModifier.Replace(e, topMember, localExpression);replaceExpression = Expression.Convert(replaceExpression, typeof(object));var compileExpression = Expression.Lambda<Func<object, object[], object>>(replaceExpression, parameter, parameters);return compileExpression.Compile();}private static Func<object, object[], object> GetStaticProperty(Expression e){var parameter = Expression.Parameter(typeof(object), "local");var parameters = Expression.Parameter(typeof(object[]), "args");var convertExpression = Expression.Convert(e, typeof(object));var compileExpression = Expression.Lambda<Func<object, object[], object>>(convertExpression, parameter, parameters);return compileExpression.Compile();}public static string GetColumnAttributeName(this MemberInfo memberInfo){return memberInfo.GetCustomAttribute<ColumnAttribute>()?.Name ?? memberInfo.Name;}public static TEntity MapToEntity<TEntity>(this Expression<Func<TEntity, TEntity>> expression){TEntity entity = Activator.CreateInstance<TEntity>();// 确保传入的是Lambda表达式if (expression.NodeType != ExpressionType.Lambda)throw new ArgumentException("Expression must be a lambda expression", nameof(expression));// 获取Lambda表达式的主体，即单个MemberExpressionvar body = ((LambdaExpression)expression).Body;// 确保Lambda表达式的主体是MemberExpression类型if (body.NodeType != ExpressionType.MemberInit)throw new ArgumentException("Expression must be a member access", nameof(expression));// 获取成员信息var memberExpression = (MemberInitExpression)body;foreach (var binding in memberExpression.Bindings){MapMemberBinding(entity, binding);}return entity;}public static void MapMemberBinding<TEntity>(TEntity target, MemberBinding binding){if (binding is MemberAssignment memberAssignment){var property = typeof(TEntity).GetProperty(memberAssignment.Member.Name);if (property != null && property.CanWrite){if (ExpressionType.MemberAccess == memberAssignment.Expression.NodeType){var constantValue = ((MemberExpression)memberAssignment.Expression).MemberToValue();property.SetValue(target, constantValue);}else if (ExpressionType.Constant == memberAssignment.Expression.NodeType){var constantExpression = (ConstantExpression)memberAssignment.Expression;property.SetValue(target, constantExpression.Value);}}}}}public class ExpressionModifier : ExpressionVisitor{public ExpressionModifier(Expression newExpression, Expression oldExpression){_newExpression = newExpression;_oldExpression = oldExpression;}private readonly Expression _newExpression;private readonly Expression _oldExpression;public Expression Replace(Expression node){return Visit(node == _oldExpression ? _newExpression : node);}public static Expression Replace(Expression node, Expression oldExpression, Expression newExpression){return new ExpressionModifier(newExpression, oldExpression).Replace(node);}}示例：
static void Main(string[] args)
{Expression<Func<MyEntity, MyEntity>> expression = (s) => new MyEntity{Age = 25,Name = "czj",};var entity = expression.MapToEntity<MyEntity>();var str = System.Text.Json.JsonSerializer.Serialize(entity);}output：
{"Age":25,"Name":"czj"}
