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

WhereClip where = new WhereClip(a => a.User_NikeName == "ssdf" || a.User_RegIP == "dddd"); where.And(a=>a.User_Email=="dddd"); where.And(a => a.User_Name == "dddd"); where.Or(a => a.User_Status > 2);

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 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(); 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; } ///

/// 改写 - 加入数据库参数特殊符号 {@} ///

/// /// 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; } ///

/// 改写-获取属性特性 ///

/// /// 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 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 args = this.VisitExpressionList(m.Arguments); if (obj != m.Object || args != m.Arguments) { return Expression.Call(obj, m.Method, args); } return m; } protected virtual ReadOnlyCollection VisitExpressionList(ReadOnlyCollection original) { List 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(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 bindings = this.VisitBindingList(binding.Bindings); if (bindings != binding.Bindings) { return Expression.MemberBind(binding.Member, bindings); } return binding; } protected virtual MemberListBinding VisitMemberListBinding(MemberListBinding binding) { IEnumerable initializers = this.VisitElementInitializerList(binding.Initializers); if (initializers != binding.Initializers) { return Expression.ListBind(binding.Member, initializers); } return binding; } protected virtual IEnumerable VisitBindingList(ReadOnlyCollection original) { List 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(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 VisitElementInitializerList(ReadOnlyCollection original) { List 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(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 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 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 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 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 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 m_fnCanBeEvaluated; private HashSet m_candidates; public PartialEvaluator() : this(CanBeEvaluatedLocally) { } public PartialEvaluator(Func 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 ///

/// Performs bottom-up analysis to determine which nodes can possibly /// be part of an evaluated sub-tree. ///

private class Nominator : ExpressionVisitor { private Func m_fnCanBeEvaluated; private HashSet m_candidates; private bool m_cannotBeEvaluated; internal Nominator(Func fnCanBeEvaluated) { this.m_fnCanBeEvaluated = fnCanBeEvaluated; } internal HashSet Nominate(Expression expression) { this.m_candidates = new HashSet(); 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 : 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> exp) { if (table == null) table = new Hashtable(); this.And(exp); } private Hashtable table; public override Hashtable Table { get { return table; } set { table = value; } } ///

/// AND 条件 ///

/// public void And(Expression> 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'); } } ///

/// OR 条件 ///

/// public void Or(Expression> 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 Not() { throw new Exception("未实现"); }public abstract class ExpressionClip : IExpressionClip { protected Expression _Expression; public abstract String WhereString { get; set; } public abstract Hashtable Table { get; set; } }

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