扩展MongoDB C# Driver的QueryBuilder
由于不想直接hardcode ClassA.MemberA.MemberB 这样的字符串 ，写了以下几个类，用于以下常用的场景：
1. 表达式转换成字符串函数： ExpToStr()
2. Collection函数：当有集合成员时，可以使用此类，将返回QueryCollection对象，这个类的代码之后附上
3. CollectionAs函数：当使用了继承，希望将基类转换为子类并返回子类的QueryCollection
使用示例：
//获得表达式的字符串形式
1. QueryEx
.ExpToStr ((ClassA m)=> m.MemberA.MemberB.MemberC)
//集合.成员.字段
//PoppedSegments为集合，AssignedNetwork.Name为成员
//将返回PoppedSegments.AssignedNetwork.Name
2. QueryEx
.Collection(x => x.PoppedSegments).Matches(p => p.AssignedNetwork.Name, bsonRegex), //子类集合.成员.字段 //STPaymentTransaction为基类，STPaymentCompanyCredit为子类，Company字段在子类中 //将返回Payments.Company.Name 3. QueryEx
.CollectionAs
(x=>x.Payments).Matches(p=>p.Company.Name, bsonRegex) //集合.集合.成员.字段 //Parcels为集合，STCustomPropertyRuntime为基类，STNumericPropertyRuntime为子类，CustomProps为STNumericPropertyRuntime中成员，Value为CustomProp中成员 //将返回Parcels.CustomProps.Value 4. QueryEx
.Collection(x=>x.Parcels).CollectionMemberAs
(p=>p.CustomProps).Matches(p=>p.Value, bsonRegex),
实现代码：
public class QueryEx
{
public static QueryCollection
Collection
( Expression
>> collectionExpression) { return new QueryCollection
(collectionExpression); } //for those cases using inheritance //e.g STPaymentTransaction //Payments will return STPaymentTransaction //need to cast to sub classes(STPaymentCompanyCredit) so that be able to filter by child members (e.g. Company) public static QueryCollection
CollectionAs
( Expression
>> collectionExpression) where TSub : TCollection { var argParam = Expression.Parameter(typeof (TDocument), x); var memberStr = ExpToStr(collectionExpression); MemberExpression nameProperty = Expression.Property(argParam, memberStr); var subExp = Expression.Convert(nameProperty, typeof(IEnumerable
)); var exp = Expression.Lambda
>>( subExp, argParam); return new QueryCollection
(exp); } ///
/// return string value for a expression: /// for s.Name.Val1.Val2 will return Name.Val1.Val2 /// ///
///
///
///
public static string ExpToStr
(Expression
> exp) { return new QueryExpressionHelper().MemberExpression(exp); } } public class QueryCollection
{ private readonly QueryExpressionHelper _queryExpression; private string _collectionName; public string Context { get { return _collectionName; } } public QueryCollection(Expression
>> collectionExpression) { _queryExpression = new QueryExpressionHelper(); _collectionName = _queryExpression.MemberExpression(collectionExpression); } public QueryMember
Member
(Expression
> exp) { var expStr = QueryEx
.ExpToStr(exp); var context = string.Format({0}.{1}, _collectionName, expStr); var obj = new QueryMember
(context); return obj; } public QueryCollection
CollectionMember
( Expression
>> exp) { var expStr = QueryEx
.ExpToStr(exp); var obj = new QueryCollection
(exp) { _collectionName = string.Format({0}.{1}, _collectionName, expStr) }; return obj; } ///
/// this method only support 1 layer nested(not for Query Collection.Collection , but for Collection.Member) /// if member is collection and need convert to sub class /// ///
Base Type
///
Child Class Type
///
///
public QueryCollection
CollectionMemberAs
( Expression
>> collectionExpression) where TMemberSub : TMember { var obj = QueryEx
.CollectionAs