Question

我正在使用LinqKit库中的PredicateBuilder类在VB.net中构建谓词。我的数据源是手动构建的数据表。我发现的所有示例都显示了创建谓词的人，然后将该谓词作为参数传递给datatable.AsEnumerable（）上的Where()方法。

但intellisense告诉我，Where()方法采用“System.Func”类型的参数，但PredicateBuilder返回的类型为“System.Linq.Expressions.Expression(Of Func(Of T, Boolean))”

我错过了什么？

示例：

        Dim ds As DataTable = getData()

        Dim tmp As IEnumerable(Of DataRow) = New DataTable().AsEnumerable()

        ' CREATE DYNAMIC LINQ WHERE CLAUSE
        Dim predicate As System.Linq.Expressions.Expression(Of Func(Of DataRow, Boolean)) = PredicateBuilder.True(Of DataRow)()

        If cbHPMS_ShowRequired.Checked Then
            predicate = predicate.And(Function(x As DataRow) x("RECORD_TYPE") = "REQUIRED")
        End If
        If cbHPMS_ShowOptional.Checked Then
            predicate = predicate.And(Function(x As DataRow) x("RECORD_TYPE") = "OPTIONAL")
        End If
        If cbHPMS_EmptyRecord.Checked Then
            predicate = predicate.And(Function(x As DataRow) x("RECORD_STATUS") = "EMPTY")
        End If
        If cbHPMS_PartialRecord.Checked Then
            predicate = predicate.And(Function(x As DataRow) x("RECORD_STATUS") = "PARTIAL")
        End If
        If cbHPMS_CompletedRecord.Checked Then
            predicate = predicate.And(Function(x As DataRow) x("RECORD_STATUS") = "COMPLETE")
        End If
        If Not String.IsNullOrEmpty(ddHPMS_RoadName.SelectedValue) And Not ddHPMS_RoadName.SelectedValue.Equals("Select") Then
            predicate = predicate.And(Function(x As DataRow) x("RoadName") = ddHPMS_RoadName.SelectedValue)
        End If

        tmp = ds.AsEnumerable().Where(predicate)

Answer 1

我没有使用LinqKit但会认为它会像

tmp = ds.AsEnumerable().Where(predicate.Compile())

PredicateBuilder，VB.net和Where（）

1 个答案: