使用Expression 生成sql update语句的时候遇到了个问题 ,Expression<Action<T>> la 这个委托里面老获取不到 引用类型的值,甚至连变量的值都不好获取 只能获取常量(ConstantExpression)的值
折腾一晚上之后终于找到解决方案
/// <summary> /// /// </summary> /// <param name="fieldMap"></param> /// <param name="sqlWhere"></param> /// <param name="transaction"></param> /// <returns></returns> public int BatchUpdateFields(Expression<Action<T>> fieldMap, string sqlWhere = "", IDbTransaction transaction = null) { if (sqlWhere == "") return 0; Type type = typeof(T); var param = ReflectionUtil.CreateInstance(typeof(T)); string result = string.Empty; MemberInitExpression binding = (MemberInitExpression)fieldMap.Body; List<string> member = new List<string>(); foreach (MemberAssignment item in binding.Bindings) { string update = item.Member.Name + "=@" + item.Member.Name; member.Add(update); PropertyInfo property = type.GetProperty(item.Member.Name); ConstantExpression ce = null; var ExpressionType = item.Expression.GetType().Name; if (ExpressionType == "PropertyExpression")//对象属性 { //妈的 这里居然要转两次 MemberExpression innerMember0 = (MemberExpression)item.Expression; MemberExpression innerMember = (MemberExpression)(innerMember0).Expression; ce = (ConstantExpression)innerMember.Expression; PropertyInfo outerProp = (PropertyInfo)item.Member; FieldInfo innerField = (FieldInfo)innerMember.Member; object innerObj = ce.Value; object outerObj = innerField.GetValue(innerObj); object value = outerProp.GetValue(outerObj, null); ReflectionUtil.SetProperty(param, item.Member.Name, value);// //ReflectionUtil 方法是一个设置对象属性值的方法 } else if (ExpressionType == "FieldExpression")//字段变量 { MemberExpression innerMember = (MemberExpression)item.Expression; ce = (ConstantExpression)innerMember.Expression; PropertyInfo outerProp = (PropertyInfo)item.Member; FieldInfo innerField = (FieldInfo)innerMember.Member; object innerObj = ce.Value; object outerObj = innerField.GetValue(innerObj); ReflectionUtil.SetProperty(param, item.Member.Name, outerObj); } else//常量参数 { ce = (ConstantExpression)item.Expression; ReflectionUtil.SetProperty(param, item.Member.Name, ce.Value); } } result = string.Join(",", member); var sql = string.Format("UPDATE {0} SET {1} WHERE {2}", TableName, string.Join(",", member), sqlWhere);
然后可以这样调用BatchUpdateFields(n => new Entity() { name= entity.name, age= entity.age, sex= entity.sex, Id = entity.Id }, " Id=@Id", null)
这样可以值更新部分字段
主要是 PropertyExpression和FieldExpression 连个类型无法和常量一样取值 需要进行转换