如何更改表达式中参数的类型？

Question

因为我在我的域中使用POCOS,我希望我的存储库能够接收我的POCOS类型的表达式过滤器,并将表达式中的参数更改为我的LINQ表的类型,我的字段具有相同的名称我的成员所以我能够通过分成成员和常量来完成1和2个lambda条件,如果我添加更多条件,这会导致递归解析二进制表达式.

这就是我的结局,是否有一个简单的方法来实现这一目标

var q = from p in 
        db.products.Where(ExpressionBuilder.Create<MyPocoProduct,LinqProduct>(myPocoProductExpression))

我改变它的方式

public class ExpressionBuilder
    {
        public static Expression<Func<TLinq, bool>> Create<TEntity, TLinq>(Expression<Func<TEntity, bool>> predicate)
        {

            try
            {
                //get the predicate body
                var binaryExpr = (BinaryExpression)predicate.Body;

                //holds the resuting Expression
                var expressionResult = default(BinaryExpression);

                // Create the parameter of the Linq table Type 
                ParameterExpression parameter = Expression.Parameter(typeof(TLinq), predicate.Parameters[0].Name);


                //if only one condition was passed
                if (binaryExpr.Left is MemberExpression)
                {
                    expressionResult = CreateExpression(binaryExpr, parameter,binaryExpr.NodeType);

                }
                else if (binaryExpr.Left is BinaryExpression)
                {
                    var predicatesList = new List<BinaryExpression>();

                    var leftExp = CreateExpression((BinaryExpression)binaryExpr.Left, parameter, binaryExpr.Left.NodeType);
                    var RightExp = CreateExpression((BinaryExpression)binaryExpr.Right, parameter, binaryExpr.Right.NodeType);

                   expressionResult = Expression.And(leftExp, RightExp);


                }

                return Expression.Lambda<Func<TLinq, bool>>(expressionResult, parameter);
            }
            catch (Exception ex)
            {
                throw new Exception("Eror While creating Filter", ex);
            }

        }

        private static BinaryExpression CreateExpression(BinaryExpression expression, ParameterExpression parameter,ExpressionType expType)
        {

            var memberExp = expression.Left as MemberExpression;

            if (memberExp == null) throw new ArgumentException("left  expression is not a member Expression");

            //create the Member expression
            MemberExpression member = LambdaExpression.PropertyOrField(parameter, memberExp.Member.Name);

            //create the constant against the value
            ConstantExpression constant = Expression.Constant(((ConstantExpression)expression.Right).Value);


            return CreateExpressionOfType(expType, member, constant);


        }


        private static BinaryExpression CreateExpressionOfType(ExpressionType expType, MemberExpression member, ConstantExpression constant)
        {

            //creates the body fo the lambda 
            var resultExpression = default(BinaryExpression);
            switch (expType)
            {

                case ExpressionType.And:
                    break;
                case ExpressionType.AndAlso:
                    break;
                case ExpressionType.ConvertChecked:
                    break;
                case ExpressionType.Equal:
                    resultExpression = Expression.Equal(member, constant);
                    break;
                case ExpressionType.ExclusiveOr:
                    break;
                case ExpressionType.GreaterThan:
                    resultExpression = Expression.GreaterThan(member, constant);
                    break;
                case ExpressionType.GreaterThanOrEqual:
                    break;
                case ExpressionType.LessThan:
                    resultExpression = Expression.LessThan(member, constant);
                    break;
                case ExpressionType.LessThanOrEqual:
                    break;
                case ExpressionType.Not:
                    break;
                case ExpressionType.NotEqual:
                    break;
                default:
                    break;
            }

            return resultExpression;


        }


    }

Answer 1

不，你不能改变 a 的类型ParameterExpression（表达式树是不可变的）；你必须重建整个树才能做到这一点。是的，你经常必须递归它。对不起...