为选定属性生成特定类型对象的动态 Linq 库

Question

我正在为我的应用程序使用动态 LINQ 库，在动态 LINQ 库的示例中， 我们可以将逗号分隔的列名称或属性名称的字符串传递给 LINQ 的 select 子句 像下面 .Select("new (AccountingDocumentNbr,DocumentFiscalYearNbr)");

我们可以传递一些对象来实例化属性值并将其填充到对象中，如下所示

.Select("new AccountingObject(AccountingDocumentNbr,DocumentFiscalYearNbr)");

AccountingObject 将具有 AccountingDocumentNbr、DocumentFiscalYearNbr。是否可以使用 Dynamic LINQ Library 来做到这一点。 http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

需要您对此的意见..

Answer 1

嗯，理论上你的代码应该是这样的：

Function ParseNew() As Expression
    NextToken()
    ValidateToken(TokenId.OpenParen, Res.OpenParenExpected)
    NextToken()
    Dim properties As New List(Of DynamicProperty)()
    Dim expressions As New List(Of Expression)()
    Do
        Dim exprPos = tokenVal.pos
        Dim expr = ParseExpression()
        Dim propName As String
        If TokenIdentifierIs("as") Then
            NextToken()
            propName = GetIdentifier()
            NextToken()
        Else
            Dim [me] As MemberExpression = TryCast(expr, MemberExpression)
            If [me] Is Nothing Then Throw ParseError(exprPos, Res.MissingAsClause)
            propName = [me].Member.Name
        End If
        expressions.Add(expr)
        properties.Add(New DynamicProperty(propName, expr.Type))
        If tokenVal.id <> TokenId.Comma Then Exit Do
        NextToken()
    Loop
    ValidateToken(TokenId.CloseParen, Res.CloseParenOrCommaExpected)
    NextToken()
    Dim type As Type = If(newResultType, DynamicExpression.CreateClass(properties))
    Dim bindings(properties.Count - 1) As MemberBinding
    For i As Integer = 0 To bindings.Length - 1
        bindings(i) = Expression.Bind(type.GetProperty(properties(i).Name), expressions(i))
    Next
    Return Expression.MemberInit(Expression.[New](type), bindings)
End Function

但是你是如何调用 Select 方法的呢？它应该或多或少像这样：

 .Select<ObjectHolder>("new (Activity as Activity, ActivityName as ActivityName)")