我正在尝试为规则引擎动态地构建表达式,在我尝试允许将嵌套类型和属性指定为操作数之前,一切都很顺利。样品:
表达式生成器
public Expression BuildExpression<T>(string propertyName, Enums.Operator ruleOperator, object value, ParameterExpression parameterExpression)
{
ExpressionType expressionType = new ExpressionType();
Expression body = parameterExpression;
foreach (var member in propertyName.Split('.'))
{
body = MemberExpression.Property(body, member);
}
var leftOperand = MemberExpression.PropertyOrField(body, propertyName);
var rightOperand = Expression.Constant(Convert.ChangeType(value, value.GetType()));
FieldInfo fieldInfo = expressionType.GetType().GetField(Enum.GetName(typeof(Enums.Operator), ruleOperator));
var expressionTypeValue = (ExpressionType)fieldInfo.GetValue(ruleOperator);
return CastBuildExpression(expressionTypeValue, value, leftOperand, rightOperand);
}
规则引擎
public Func<T, bool>[] CombineRules<T>(Criterion[] criteria)
{
List<Func<T, bool>> list = new List<Func<T, bool>>();
foreach (var criterion in criteria)
{
ExpressionBuilder expressionBuilder = new ExpressionBuilder();
var param = Expression.Parameter(typeof (T));
Expression expression = expressionBuilder.BuildExpression<T>(criterion.PropertyName,
criterion.Operator_, criterion.Value, param);
Func<T, bool> func = Expression.Lambda<Func<T, bool>>(expression, param).Compile();
list.Add(func);
}
return list.ToArray();
}
标准
public class Criterion
{
private bool propertySet;
public string PropertyName { get; set; }
public Enums.Operator Operator_ { get; set; }
public object Value { get; set; }
成员模型
public class MemberModel
{
public string UserName{ get; set; }
public PersonalDetailsModel PersonalDetails {get; set;}
}
个性化详细信息模型
public class PersonalDetailsModel
{
public int PersonalDetailsId { get; set; }
public string Firstname { get; set; }
public string Lastname { get; set; }
public string Middlename { get; set; }
public string DateOfBirth { get; set; }
public string GenderType { get; set; }
public string SalutationType { get; set; }
}
当我试图将嵌套属性作为左操作数传入ruleengine.combinerules(criteria.toArray())时,就会出现问题;
我得到的“personaldetails.firstname”不是“system.string”类型的成员,尽管它显然是这样。我被困在这件事上有一段时间了,知道是什么原因吗?
任何帮助都将不胜感激。
最佳答案
在这里
Expression body = parameterExpression;
foreach (var member in propertyName.Split('.'))
{
body = MemberExpression.Property(body, member);
}
您已经处理了属性路径,因此
var leftOperand = MemberExpression.PropertyOrField(body, propertyName);
毫无意义,是异常的根源。在您的示例中,
body
包含类似于p.PersonalDetails.FirstName
(字符串)的内容,上面的行试图构建类似于p.PersonalDetails.FirstName.PersonalDetails.FirstName
的内容。改为使用
var leftOperand = body;
。您可以使用简单的
var leftOperand = propertyName.Split('.')
.Aggregate((Expression)parameterExpression, Expression.PropertyOrField);