拉姆达表达式转对象(太给力啦！)

在自己做框架时候遇到一个对条件拼装问题。用lambda写法却无法转换成对象加以组合。直到找到下面这些代码

那么可以直接将lambda表达式解析成SQL条件语句

如下

(([User_NikeName] = @User_NikeName) OR ([User_RegIP] = @User_RegIP))AND([User_Email] = @User_Email)AND([User_Name] = @User_Name)AND([User_Status] > @User_Status)

当然我自己加上了参数化了，具体如何写可以适当加以改写

主要代码：

internal class ConditionBuilder : ExpressionVisitor
  {
    private Hashtable m_arguments;
    private Stack<string> m_conditionParts;

public string Condition { get; private set; }

public Hashtable Arguments { get; private set; }

public void Build(Expression expression)
    {
      PartialEvaluator evaluator = new PartialEvaluator();
      Expression evaluatedExpression = evaluator.Eval(expression);

this.m_arguments = new Hashtable();
      this.m_conditionParts = new Stack<string>();

this.Visit(evaluatedExpression);

this.Arguments = m_arguments;
      this.Condition = this.m_conditionParts.Count > 0 ? this.m_conditionParts.Pop() : null;
    }

protected override Expression VisitBinary(BinaryExpression b)
    {
      if (b == null) return b;

string opr;
      switch (b.NodeType)
      {
        case ExpressionType.Equal:
          opr = "=";
          break;
        case ExpressionType.NotEqual:
          opr = "<>";
          break;
        case ExpressionType.GreaterThan:
          opr = ">";
          break;
        case ExpressionType.GreaterThanOrEqual:
          opr = ">=";
          break;
        case ExpressionType.LessThan:
          opr = "<";
          break;
        case ExpressionType.LessThanOrEqual:
          opr = "<=";
          break;
        case ExpressionType.AndAlso:
          opr = "AND";
          break;
        case ExpressionType.OrElse:
          opr = "OR";
          break;
        case ExpressionType.Add:
          opr = "+";
          break;
        case ExpressionType.Subtract:
          opr = "-";
          break;
        case ExpressionType.Multiply:
          opr = "*";
          break;
        case ExpressionType.Divide:
          opr = "/";
          break;
        default:
          throw new NotSupportedException(b.NodeType + "is not supported.");
      }

this.Visit(b.Left);
      this.Visit(b.Right);

string right = this.m_conditionParts.Pop();
      string left = this.m_conditionParts.Pop();

string condition = String.Format("({0} {1} {2})", left, opr, right);
      this.m_conditionParts.Push(condition);

return b;
    }

/// <summary>
    /// 改写 - 加入数据库参数特殊符号 {@}
    /// </summary>
    /// <param name="c"></param>
    /// <returns></returns>
    protected override Expression VisitConstant(ConstantExpression c)
    {
      if (c == null) return c;

this.m_arguments.Add(m_conditionParts.ToList()[0].Trim('[', ']'), c.Value);

this.m_conditionParts.Push(String.Format("{0}", DbFactoryProviderUser.Provider.GetDbParmChar()) + m_conditionParts.ToList()[0].Trim('[',']'));

return c;
    }

/// <summary>
    /// 改写-获取属性特性
    /// </summary>
    /// <param name="m"></param>
    /// <returns></returns>
    protected override Expression VisitMemberAccess(MemberExpression m)
    {
      if (m == null) return m;

PropertyInfo propertyInfo = m.Member as PropertyInfo;

if (propertyInfo == null) return m;

this.m_conditionParts.Push(String.Format("[{0}]", propertyInfo.Name));

return m;
    }
  }

public abstract class ExpressionVisitor
    {
        protected ExpressionVisitor() { }

protected virtual Expression Visit(Expression exp)
        {
            if (exp == null)
                return exp;
            switch (exp.NodeType)
            {
                case ExpressionType.Negate:
                case ExpressionType.NegateChecked:
                case ExpressionType.Not:
                case ExpressionType.Convert:
                case ExpressionType.ConvertChecked:
                case ExpressionType.ArrayLength:
                case ExpressionType.Quote:
                case ExpressionType.TypeAs:
                    return this.VisitUnary((UnaryExpression)exp);
                case ExpressionType.Add:
                case ExpressionType.AddChecked:
                case ExpressionType.Subtract:
                case ExpressionType.SubtractChecked:
                case ExpressionType.Multiply:
                case ExpressionType.MultiplyChecked:
                case ExpressionType.Divide:
                case ExpressionType.Modulo:
                case ExpressionType.And:
                case ExpressionType.AndAlso:
                case ExpressionType.Or:
                case ExpressionType.OrElse:
                case ExpressionType.LessThan:
                case ExpressionType.LessThanOrEqual:
                case ExpressionType.GreaterThan:
                case ExpressionType.GreaterThanOrEqual:
                case ExpressionType.Equal:
                case ExpressionType.NotEqual:
                case ExpressionType.Coalesce:
                case ExpressionType.ArrayIndex:
                case ExpressionType.RightShift:
                case ExpressionType.LeftShift:
                case ExpressionType.ExclusiveOr:
                    return this.VisitBinary((BinaryExpression)exp);
                case ExpressionType.TypeIs:
                    return this.VisitTypeIs((TypeBinaryExpression)exp);
                case ExpressionType.Conditional:
                    return this.VisitConditional((ConditionalExpression)exp);
                case ExpressionType.Constant:
                    return this.VisitConstant((ConstantExpression)exp);
                case ExpressionType.Parameter:
                    return this.VisitParameter((ParameterExpression)exp);
                case ExpressionType.MemberAccess:
                    return this.VisitMemberAccess((MemberExpression)exp);
                case ExpressionType.Call:
                    return this.VisitMethodCall((MethodCallExpression)exp);
                case ExpressionType.Lambda:
                    return this.VisitLambda((LambdaExpression)exp);
                case ExpressionType.New:
                    return this.VisitNew((NewExpression)exp);
                case ExpressionType.NewArrayInit:
                case ExpressionType.NewArrayBounds:
                    return this.VisitNewArray((NewArrayExpression)exp);
                case ExpressionType.Invoke:
                    return this.VisitInvocation((InvocationExpression)exp);
                case ExpressionType.MemberInit:
                    return this.VisitMemberInit((MemberInitExpression)exp);
                case ExpressionType.ListInit:
                    return this.VisitListInit((ListInitExpression)exp);
                default:
                    throw new Exception(string.Format("Unhandled expression type: '{0}'", exp.NodeType));
            }
        }

protected virtual MemberBinding VisitBinding(MemberBinding binding)
        {
            switch (binding.BindingType)
            {
                case MemberBindingType.Assignment:
                    return this.VisitMemberAssignment((MemberAssignment)binding);
                case MemberBindingType.MemberBinding:
                    return this.VisitMemberMemberBinding((MemberMemberBinding)binding);
                case MemberBindingType.ListBinding:
                    return this.VisitMemberListBinding((MemberListBinding)binding);
                default:
                    throw new Exception(string.Format("Unhandled binding type '{0}'", binding.BindingType));
            }
        }

protected virtual ElementInit VisitElementInitializer(ElementInit initializer)
        {
            ReadOnlyCollection<Expression> arguments = this.VisitExpressionList(initializer.Arguments);
            if (arguments != initializer.Arguments)
            {
                return Expression.ElementInit(initializer.AddMethod, arguments);
            }
            return initializer;
        }

protected virtual Expression VisitUnary(UnaryExpression u)
        {
            Expression operand = this.Visit(u.Operand);
            if (operand != u.Operand)
            {
                return Expression.MakeUnary(u.NodeType, operand, u.Type, u.Method);
            }
            return u;
        }

protected virtual Expression VisitBinary(BinaryExpression b)
        {
            Expression left = this.Visit(b.Left);
            Expression right = this.Visit(b.Right);
            Expression conversion = this.Visit(b.Conversion);
            if (left != b.Left || right != b.Right || conversion != b.Conversion)
            {
                if (b.NodeType == ExpressionType.Coalesce && b.Conversion != null)
                    return Expression.Coalesce(left, right, conversion as LambdaExpression);
                else
                    return Expression.MakeBinary(b.NodeType, left, right, b.IsLiftedToNull, b.Method);
            }
            return b;
        }

protected virtual Expression VisitTypeIs(TypeBinaryExpression b)
        {
            Expression expr = this.Visit(b.Expression);
            if (expr != b.Expression)
            {
                return Expression.TypeIs(expr, b.TypeOperand);
            }
            return b;
        }

protected virtual Expression VisitConstant(ConstantExpression c)
        {
            return c;
        }

protected virtual Expression VisitConditional(ConditionalExpression c)
        {
            Expression test = this.Visit(c.Test);
            Expression ifTrue = this.Visit(c.IfTrue);
            Expression ifFalse = this.Visit(c.IfFalse);
            if (test != c.Test || ifTrue != c.IfTrue || ifFalse != c.IfFalse)
            {
                return Expression.Condition(test, ifTrue, ifFalse);
            }
            return c;
        }

protected virtual Expression VisitParameter(ParameterExpression p)
        {
            return p;
        }

protected virtual Expression VisitMemberAccess(MemberExpression m)
        {
            Expression exp = this.Visit(m.Expression);
            if (exp != m.Expression)
            {
                return Expression.MakeMemberAccess(exp, m.Member);
            }
            return m;
        }

protected virtual Expression VisitMethodCall(MethodCallExpression m)
        {
            Expression obj = this.Visit(m.Object);
            IEnumerable<Expression> args = this.VisitExpressionList(m.Arguments);
            if (obj != m.Object || args != m.Arguments)
            {
                return Expression.Call(obj, m.Method, args);
            }
            return m;
        }

protected virtual ReadOnlyCollection<Expression> VisitExpressionList(ReadOnlyCollection<Expression> original)
        {
            List<Expression> list = null;
            for (int i = 0, n = original.Count; i < n; i++)
            {
                Expression p = this.Visit(original[i]);
                if (list != null)
                {
                    list.Add(p);
                }
                else if (p != original[i])
                {
                    list = new List<Expression>(n);
                    for (int j = 0; j < i; j++)
                    {
                        list.Add(original[j]);
                    }
                    list.Add(p);
                }
            }
            if (list != null)
            {
                return list.AsReadOnly();
            }
            return original;
        }

protected virtual MemberAssignment VisitMemberAssignment(MemberAssignment assignment)
        {
            Expression e = this.Visit(assignment.Expression);
            if (e != assignment.Expression)
            {
                return Expression.Bind(assignment.Member, e);
            }
            return assignment;
        }

protected virtual MemberMemberBinding VisitMemberMemberBinding(MemberMemberBinding binding)
        {
            IEnumerable<MemberBinding> bindings = this.VisitBindingList(binding.Bindings);
            if (bindings != binding.Bindings)
            {
                return Expression.MemberBind(binding.Member, bindings);
            }
            return binding;
        }

protected virtual MemberListBinding VisitMemberListBinding(MemberListBinding binding)
        {
            IEnumerable<ElementInit> initializers = this.VisitElementInitializerList(binding.Initializers);
            if (initializers != binding.Initializers)
            {
                return Expression.ListBind(binding.Member, initializers);
            }
            return binding;
        }

protected virtual IEnumerable<MemberBinding> VisitBindingList(ReadOnlyCollection<MemberBinding> original)
        {
            List<MemberBinding> list = null;
            for (int i = 0, n = original.Count; i < n; i++)
            {
                MemberBinding b = this.VisitBinding(original[i]);
                if (list != null)
                {
                    list.Add(b);
                }
                else if (b != original[i])
                {
                    list = new List<MemberBinding>(n);
                    for (int j = 0; j < i; j++)
                    {
                        list.Add(original[j]);
                    }
                    list.Add(b);
                }
            }
            if (list != null)
                return list;
            return original;
        }

protected virtual IEnumerable<ElementInit> VisitElementInitializerList(ReadOnlyCollection<ElementInit> original)
        {
            List<ElementInit> list = null;
            for (int i = 0, n = original.Count; i < n; i++)
            {
                ElementInit init = this.VisitElementInitializer(original[i]);
                if (list != null)
                {
                    list.Add(init);
                }
                else if (init != original[i])
                {
                    list = new List<ElementInit>(n);
                    for (int j = 0; j < i; j++)
                    {
                        list.Add(original[j]);
                    }
                    list.Add(init);
                }
            }
            if (list != null)
                return list;
            return original;
        }

protected virtual Expression VisitLambda(LambdaExpression lambda)
        {
            Expression body = this.Visit(lambda.Body);
            if (body != lambda.Body)
            {
                return Expression.Lambda(lambda.Type, body, lambda.Parameters);
            }
            return lambda;
        }

protected virtual NewExpression VisitNew(NewExpression nex)
        {
            IEnumerable<Expression> args = this.VisitExpressionList(nex.Arguments);
            if (args != nex.Arguments)
            {
                if (nex.Members != null)
                    return Expression.New(nex.Constructor, args, nex.Members);
                else
                    return Expression.New(nex.Constructor, args);
            }
            return nex;
        }

protected virtual Expression VisitMemberInit(MemberInitExpression init)
        {
            NewExpression n = this.VisitNew(init.NewExpression);
            IEnumerable<MemberBinding> bindings = this.VisitBindingList(init.Bindings);
            if (n != init.NewExpression || bindings != init.Bindings)
            {
                return Expression.MemberInit(n, bindings);
            }
            return init;
        }

protected virtual Expression VisitListInit(ListInitExpression init)
        {
            NewExpression n = this.VisitNew(init.NewExpression);
            IEnumerable<ElementInit> initializers = this.VisitElementInitializerList(init.Initializers);
            if (n != init.NewExpression || initializers != init.Initializers)
            {
                return Expression.ListInit(n, initializers);
            }
            return init;
        }

protected virtual Expression VisitNewArray(NewArrayExpression na)
        {
            IEnumerable<Expression> exprs = this.VisitExpressionList(na.Expressions);
            if (exprs != na.Expressions)
            {
                if (na.NodeType == ExpressionType.NewArrayInit)
                {
                    return Expression.NewArrayInit(na.Type.GetElementType(), exprs);
                }
                else
                {
                    return Expression.NewArrayBounds(na.Type.GetElementType(), exprs);
                }
            }
            return na;
        }

protected virtual Expression VisitInvocation(InvocationExpression iv)
        {
            IEnumerable<Expression> args = this.VisitExpressionList(iv.Arguments);
            Expression expr = this.Visit(iv.Expression);
            if (args != iv.Arguments || expr != iv.Expression)
            {
                return Expression.Invoke(expr, args);
            }
            return iv;
        }
    }

public class PartialEvaluator : ExpressionVisitor
    {
        private Func<Expression, bool> m_fnCanBeEvaluated;
        private HashSet<Expression> m_candidates;

public PartialEvaluator()
            : this(CanBeEvaluatedLocally)
        { }

public PartialEvaluator(Func<Expression, bool> fnCanBeEvaluated)
        {
            this.m_fnCanBeEvaluated = fnCanBeEvaluated;
        }

public Expression Eval(Expression exp)
        {
            this.m_candidates = new Nominator(this.m_fnCanBeEvaluated).Nominate(exp);

return this.Visit(exp);
        }

protected override Expression Visit(Expression exp)
        {
            if (exp == null)
            {
                return null;
            }

if (this.m_candidates.Contains(exp))
            {
                return this.Evaluate(exp);
            }

return base.Visit(exp);
        }

private Expression Evaluate(Expression e)
        {
            if (e.NodeType == ExpressionType.Constant)
            {
                return e;
            }

LambdaExpression lambda = Expression.Lambda(e);
            Delegate fn = lambda.Compile();

return Expression.Constant(fn.DynamicInvoke(null), e.Type);
        }

private static bool CanBeEvaluatedLocally(Expression exp)
        {
            return exp.NodeType != ExpressionType.Parameter;
        }

#region Nominator

/// <summary>
        /// Performs bottom-up analysis to determine which nodes can possibly
        /// be part of an evaluated sub-tree.
        /// </summary>
        private class Nominator : ExpressionVisitor
        {
            private Func<Expression, bool> m_fnCanBeEvaluated;
            private HashSet<Expression> m_candidates;
            private bool m_cannotBeEvaluated;

internal Nominator(Func<Expression, bool> fnCanBeEvaluated)
            {
                this.m_fnCanBeEvaluated = fnCanBeEvaluated;
            }

internal HashSet<Expression> Nominate(Expression expression)
            {
                this.m_candidates = new HashSet<Expression>();
                this.Visit(expression);
                return this.m_candidates;
            }

protected override Expression Visit(Expression expression)
            {
                if (expression != null)
                {
                    bool saveCannotBeEvaluated = this.m_cannotBeEvaluated;
                    this.m_cannotBeEvaluated = false;

base.Visit(expression);

if (!this.m_cannotBeEvaluated)
                    {
                        if (this.m_fnCanBeEvaluated(expression))
                        {
                            this.m_candidates.Add(expression);
                        }
                        else
                        {
                            this.m_cannotBeEvaluated = true;
                        }
                    }

this.m_cannotBeEvaluated |= saveCannotBeEvaluated;
                }

return expression;
            }
        }

#endregion
    }

public class WhereClip<T> : ExpressionClip where T : BaseEntity
  {
    public WhereClip()
    {
      if (table == null)
        table = new Hashtable();
    }
    private String whereString;

public override String WhereString
    {
      get { return whereString; }
      set { whereString = value; }
    }

public WhereClip(Expression<Func<T, bool>> exp)
    {
      if (table == null)
        table = new Hashtable();
      this.And(exp);
    }

private Hashtable table;

public override Hashtable Table
    {
      get { return table; }
      set
      {
        table = value;
      }
    }

/// <summary>
    /// AND 条件
    /// </summary>
    /// <param name="right"></param>
    public void And(Expression<Func<T, bool>> right)
    {
      ConditionBuilder conditionBuilder = new ConditionBuilder();
      conditionBuilder.Build(right.Body);
      if (!String.IsNullOrEmpty(conditionBuilder.Condition))
      {
        whereString += "AND" + conditionBuilder.Condition;
      }
      foreach (DictionaryEntry item in conditionBuilder.Arguments)
      {
        if (!table.ContainsKey(item.Key))
          table.Add(item.Key, item.Value);
        else
          table[item.Key] = item.Value;
      }

//替换开始字符
      if (whereString.StartsWith("AND"))
      {
        whereString = WhereString.TrimStart('A', 'N', 'D');
      }
    }

/// <summary>
    /// OR 条件
    /// </summary>
    /// <param name="right"></param>
    public void Or(Expression<Func<T, bool>> right)
    {
      ConditionBuilder conditionBuilder = new ConditionBuilder();
      conditionBuilder.Build(right.Body);
      if (!String.IsNullOrEmpty(conditionBuilder.Condition))
      {
        whereString += "OR" + conditionBuilder.Condition;
      }
      foreach (DictionaryEntry item in conditionBuilder.Arguments)
      {
        if (!table.ContainsKey(item.Key))
          table.Add(item.Key, item.Value);
        else
          table[item.Key] = item.Value;
      }

if (whereString.StartsWith("OR"))
      {
        whereString = WhereString.TrimStart('O', 'R');
      }
    }

public WhereClip<T> Not()
    {

throw new Exception("未实现");
    }

代码下载地址：

CSDN： http://download.csdn.net/detail/ysq5202121/4251354

老赵： http://www.cnblogs.com/jeffreyzhao/archive/2008/03/05/linq-to-sql-batch-delete-extension.html

拉姆达表达式转对象(太给力啦！)

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