//基类
class baseEntity
{internal Expression whereFunc;
}

//实体对象
class Article_Content : baseEntity
{public int? Article_Id { get; set; }public string Article_Title { get; set; }public string Article_SourceUrl { get; set; }
}

/// <summary>
/// 设置匹配表达式
/// </summary>
public static void SetWhereFunc<T>(this T entity, Expression<Func<T, bool>> func) where T : baseEntity
{
entity.whereFunc = func;
}

好了。这个时候我们可以写出类似下面的代码了：

Article_Content art = new Article_Content();
art.SetWhereFunc(ar=>ar.Aritlce_Id == 4 && ar.Article_Title == "sss");

public static bool In<T>(this T obj, T[] array)
{return true;
}
public static bool Like(this string str, string likeStr)
{return true;
}

art.SetWhereFunc(ar=>ar.Aritlce_Id.In(new int?[]{4,6}) && ar.Article_Title.Like("%sss"));

到目前为止，前台编写方式已经解决了。

剩下的就是如何来分析我们设置的这个lambda表达式了。

当然分析lambda表达式的时候，我们还需要考虑生成的SQL语句的参数化。这个时候还需要另一个数据操作对象：

public abstract class DbOperate
{/// <summary>/// 获取此数据类型的参数形式表现/// </summary>/// <param name="fieldsName"></param>/// <returns></returns>public abstract string GetParamFlag(string fieldsName);//其他操作方法.....

}

internal static string Where<T>(this T entity, Expression func, DbOperate dbop, ref ArrayList alParamNames, ref ArrayList alParamValues) where T : baseEntity
{return ExpressionRouter(func, dbop, ref alParamNames, ref alParamValues);
} 

lambda表达式也是表达式的一种。那么我们可以通过分析表达式的类型计算对应的产生式。

现在主要遇到的表达式有以下几种：

1. BinaryExpression
2. LambdaExpression
3. MethodCallExpression
4. MemberExpression
5. ConstantExpression
6. NewArrayExpression
7. UnaryExpression

static string BinarExpressionProvider(Expression left, Expression right, ExpressionType type){string sb = "(";//先处理左边sb += ExpressionRouter(left);sb += ExpressionTypeCast(type);//再处理右边string tmpStr = ExpressionRouter(right);if (tmpStr == "null"){if (sb.EndsWith(" ="))sb = sb.Substring(0, sb.Length - 2) + " is null";else if (sb.EndsWith("<>"))sb = sb.Substring(0, sb.Length - 2) + " is not null";}elsesb += tmpStr;return sb += ")";}//表达式路由计算 static string ExpressionRouter(Expression exp){string sb = string.Empty;if (exp is BinaryExpression){BinaryExpression be = ((BinaryExpression)exp);return BinarExpressionProvider(be.Left, be.Right, be.NodeType);}else if (exp is MemberExpression){MemberExpression me = ((MemberExpression)exp);return me.Member.Name;}else if (exp is NewArrayExpression){NewArrayExpression ae = ((NewArrayExpression)exp);StringBuilder tmpstr = new StringBuilder();foreach (Expression ex in ae.Expressions){tmpstr.Append(ExpressionRouter(ex));tmpstr.Append(",");}return tmpstr.ToString(0, tmpstr.Length - 1);}else if (exp is MethodCallExpression){MethodCallExpression mce = (MethodCallExpression)exp;if (mce.Method.Name == "Like")return string.Format("({0} like {1})", ExpressionRouter(mce.Arguments[0]), ExpressionRouter(mce.Arguments[1]));else if (mce.Method.Name == "NotLike")return string.Format("({0} Not like {1})", ExpressionRouter(mce.Arguments[0]), ExpressionRouter(mce.Arguments[1]));else if (mce.Method.Name == "In")return string.Format("{0} In ({1})", ExpressionRouter(mce.Arguments[0]), ExpressionRouter(mce.Arguments[1]));else if (mce.Method.Name == "NotIn")return string.Format("{0} Not In ({1})", ExpressionRouter(mce.Arguments[0]), ExpressionRouter(mce.Arguments[1]));}else if (exp is ConstantExpression){ConstantExpression ce = ((ConstantExpression)exp);if (ce.Value == null)return "null";else if (ce.Value is ValueType)return ce.Value.ToString();else if (ce.Value is string || ce.Value is DateTime || ce.Value is char)return string.Format("'{0}'", ce.Value.ToString());}else if (exp is UnaryExpression){UnaryExpression ue = ((UnaryExpression)exp);return ExpressionRouter(ue.Operand);}return null;}static string ExpressionTypeCast(ExpressionType type){switch (type){case ExpressionType.And:case ExpressionType.AndAlso:return " AND ";case ExpressionType.Equal:return " =";case ExpressionType.GreaterThan:return " >";case ExpressionType.GreaterThanOrEqual:return ">=";case ExpressionType.LessThan:return "<";case ExpressionType.LessThanOrEqual:return "<=";case ExpressionType.NotEqual:return "<>";case ExpressionType.Or:case ExpressionType.OrElse:return " Or ";case ExpressionType.Add:case ExpressionType.AddChecked:return "+";case ExpressionType.Subtract:case ExpressionType.SubtractChecked:return "-";case ExpressionType.Divide:return "/";case ExpressionType.Multiply:case ExpressionType.MultiplyChecked:return "*";default:return null;}}

string.Concat(GetStr(7), "sdfsdf".Length, "sssss" + GetStr(6)).ToUpper()