[英]PredicateBuilder, VB.net and Where()
I am building a predicate in VB.net using the PredicateBuilder class from the LinqKit library.我正在使用 LinqKit 库中的 PredicateBuilder class 在 VB.net 中构建谓词。 My datasource is a manually constructed datatable.我的数据源是手动构建的数据表。 All the examples I've found show folks creating the predicate and then passing that predicate as an argument to the Where()
method on the datatable.AsEnumerable().我发现的所有示例都显示人们创建谓词,然后将该谓词作为参数传递给 datatable.AsEnumerable() 上的Where()
方法。
But intellisense is telling me that the Where()
method takes a paremeter of type " System.Func
", but the type returned by PredicateBuilder is " System.Linq.Expressions.Expression(Of Func(Of T, Boolean))
"但是智能感知告诉我Where()
方法采用“ System.Func
”类型的参数,但 PredicateBuilder 返回的类型是“ System.Linq.Expressions.Expression(Of Func(Of T, Boolean))
”
What am I missing?我错过了什么?
Example:例子:
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)
I have not used LinqKit but would think it would be like我没有使用过 LinqKit,但会认为它会像
tmp = ds.AsEnumerable().Where(predicate.Compile())
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