我的WCF数据服务（四）涅槃

灰太狼 2022-09-25 10:19 210阅读 0赞

网站以上面的方式运行了一段时间，速度很好。但是，心中隐隐有所不甘，本来 Lambda 表达式就是为了方便，如果都这样写，反倒要费事了。既然我能自己构建表达式，为什么不能改造已有的表达式呢？于是经过各种研究，反复试验，终于出炉了我觉得比较满意的一个表达式转换类。当用户在调用查询时，会使用这个类重建一个表达式，把里面的进程内变量替换成值。代码如下：

using System.Collections.Generic;
    namespace System.Linq.Expressions
    {
        public class ExpressionRebuilder<T, Tk> where T : class
        {
            public Expression<Func<T, Tk>> Result;
            public ExpressionRebuilder(Expression<Func<T, Tk>> predicate)
            {
                Result = Expression.Lambda(Rebuild(predicate.Body), predicate.Parameters) as Expression<Func<T, Tk>>;
            }
    
            private Expression Rebuild(Expression exp)
            {
                if (exp is BinaryExpression)
                    return Rebuild((BinaryExpression)exp);
                else if (exp is MethodCallExpression)
                    return Rebuild((MethodCallExpression)exp);
                else if (exp is ConstantExpression)
                    return exp;
                else if (exp is UnaryExpression)
                    return Rebuild((UnaryExpression)exp);
                else if (exp is MemberExpression)
                    return Rebuild((MemberExpression)exp);
                else if (exp is ConditionalExpression)
                    return Rebuild((ConditionalExpression)exp);
                else
                    return exp;
            }
    
            private Expression Rebuild(UnaryExpression @Unary)
            {
                ExpressionType nt = @Unary.NodeType;
                Expression op = @Unary.Operand;
                if (nt == ExpressionType.Not)
                {
                    op = Rebuild(op);
                    return Expression.Not(op);
                }
                else if (nt == ExpressionType.Convert)
                {
                    if (op is MemberExpression)
                    {
                        op = Rebuild((MemberExpression)op);
                    }
                    if (op is ConstantExpression)
                    {
                        op = Expression.Convert(op, @Unary.Type);
                        op = Expression.Constant(Expression.Lambda(op).Compile().DynamicInvoke(), @Unary.Type);
                        return op;
                    }
                    else
                        return Expression.Convert(op, @Unary.Type);
                }
                else
                    return @Unary;
            }
    
            private Expression Rebuild(MethodCallExpression @MethodCall)
            {
                var a = @MethodCall.Arguments;
                var rstArguments = new List<Expression>();
                var obj = @MethodCall.Object;
                if (obj != null)
                {
                    if (obj.Type == typeof(System.Web.HttpRequest) && @MethodCall.Method.Name == "get_Item")
                    {
                        System.Web.HttpRequest swhr = (System.Web.HttpRequest)(((ConstantExpression)Rebuild((MemberExpression)obj)).Value);
                        object o = ((ConstantExpression)a[0]).Value;
                        string ag = swhr[o.ToString()];
                        return Expression.Constant(ag, typeof(string));
                    }
                    obj = Rebuild(obj);
                }
    
                foreach (var aa in a)
                {
                    var bb = Rebuild(aa);
                    rstArguments.Add(bb);
                }
                MethodCallExpression mce;
                if (obj == null)
                {
                    mce = Expression.Call(@MethodCall.Method, rstArguments);
                }
                else
                {
                    mce = Expression.Call(obj, @MethodCall.Method, rstArguments);
                }
                return ReduceMethodCallExpression(mce);
            }
    
            Expression ReduceMethodCallExpression(MethodCallExpression @MethodCall)
            {
                object o = @MethodCall.Object;
                if (o != null && !(o is ConstantExpression))
                    return @MethodCall;
                bool allTrue = true;
                foreach (Expression a in @MethodCall.Arguments)
                {
                    if (!(a is ConstantExpression))
                    {
                        allTrue = false;
                        break;
                    }
                }
                if (!allTrue)
                    return @MethodCall;
                List<object> lo = new List<object>();
                foreach (Expression a in @MethodCall.Arguments)
                {
                    lo.Add(((ConstantExpression)a).Value);
                }
                object rsst = @MethodCall.Method.Invoke(o == null ? o : ((ConstantExpression)o).Value, lo.ToArray());
    
                return Expression.Constant(rsst);
            }
    
            private Expression Rebuild(BinaryExpression @Binary)
            {
                Expression l = @Binary.Left;
                Expression r = @Binary.Right;
    
                l = Rebuild(l);
    
                r = Rebuild(r);
    
                if (l is ConstantExpression && r is ConstantExpression)
                {
                    if (@Binary.NodeType == ExpressionType.ArrayIndex)
                    {
                        return Expression.Constant(((object[])(((ConstantExpression)l).Value))[(int)((ConstantExpression)r).Value]);
                    }
                }
                if (@Binary.NodeType == ExpressionType.AndAlso)
                {
                    if (l is ConstantExpression)
                    {
                        var lc = (ConstantExpression)l;
                        if (lc.Type == typeof(bool))
                        {
                            bool lcb = (bool)lc.Value;
                            if (lcb)
                                return r;
                            else
                                return Expression.Constant(false, typeof(bool));
                        }
                    }
                    if (r is ConstantExpression)
                    {
                        var rc = (ConstantExpression)r;
                        if (rc.Type == typeof(bool))
                        {
                            bool rcb = (bool)rc.Value;
                            if (rcb)
                                return l;
                            else
                                return Expression.Constant(false, typeof(bool));
                        }
                    }
                }
                BinaryExpression be = Expression.MakeBinary(@Binary.NodeType, l, r, @Binary.IsLiftedToNull, @Binary.Method);
                if (l is ConstantExpression && r is ConstantExpression)
                {
                    try
                    {
                        object o = Expression.Lambda(be).Compile().DynamicInvoke();
                        return Expression.Constant(o, be.Type);
                    }
                    catch (Exception) { }
                }
                return be;
            }
    
            private Expression Rebuild(ConditionalExpression Ce)
            {
                Expression newTest = Rebuild(Ce.Test);
                Expression newIfTrue = Rebuild(Ce.IfTrue);
                Expression newIfFalse = Rebuild(Ce.IfFalse);
                if (newTest is ConstantExpression)
                {
                    ConstantExpression nt = (ConstantExpression)newTest;
                    if (nt.Type == typeof(bool))
                    {
                        bool b = (bool)nt.Value;
                        if (b)
                            return newIfTrue;
                        else
                            return newIfFalse;
                    }
                }
                return Expression.Condition(newTest, newIfTrue, newIfFalse);
            }
    
            private Expression Rebuild(MemberExpression Me)
            {
                if (Me.Expression != null && Me.Expression.NodeType == ExpressionType.Parameter)
                {
                    return Me;
                }
                var rst = Me.Expression;
                if (rst is MemberExpression)
                {
                    rst = Rebuild((MemberExpression)rst);
                }
                try
                {
                    object o = Expression.Lambda(Me).Compile().DynamicInvoke();
                    return Expression.Constant(o, Me.Type);
                }
                catch (Exception) { }
                //下面的内容是先写的，有时会报错，后来使用了上边的DynamicInvoke()
                if (!(rst is ConstantExpression))
                    return Me;
                var b = ((ConstantExpression)rst).Value;
                System.Reflection.FieldInfo fi;
                fi = b.GetType().GetField(Me.Member.Name, System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
                if (fi == null)
                    fi = b.GetType().GetField(Me.Member.Name);
                if (fi != null)
                {
                    object c = fi.GetValue(b);
                    ConstantExpression ce = Expression.Constant(c, Me.Type);
                    return ce;
                }
                else
                {
                    System.Reflection.PropertyInfo pi = b.GetType().GetProperty(Me.Member.Name);
                    if (pi == null)
                        pi = b.GetType().GetProperty(Me.Member.Name, System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
                    object c = pi.GetValue(b);
                    ConstantExpression ce = Expression.Constant(c, Me.Type);
                    return ce;
                }
            }
        }
    }

调用时这样：

predicate ＝ new System.Linq.Expressions.ExpressionRebuilder<Model.XXX, bool>(predicate).Result;

写到了扩展方法里：

public static Expression<Func<T,Tk>> Rebuild<T,Tk>(this Expression<Func<T, Tk>> predicate) where T:class
            {
                return new System.Linq.Expressions.ExpressionRebuilder<T, Tk>(predicate).Result;
            }

在BLL.XXX里，只要这样一句就够了：

public List<T> GetList<Tm>(int pageSize, int pageIndex, Expression<Func<T, bool>> Efma, Expression<Func<T, Tm>> orderBy, bool desc, out int recordCount)
    {
         Efma = Efma.Rebuild();
         return WCF.GetList(pageSize, pageIndex, Efmas, keySelector, desc, out recordCount);
    }

这几年中，网站扩大了，手下多了几个人。他们调用数据服务时，和调用进程内的数据没有什么区别，再也不用写很长的代码，对他们来说是透明的。  
最终实现了类似内存数据库的东西，速度比数据库要快几倍，并发性能也要高很多，因为是直接从内存检索数据。  
这个类是我第一个比较满意的作品，如果有什么问题和意见，欢迎评论。