Question

如何使用LINQ将此查询写入FoxPro数据库？

SELECT count(*) FROM Table group by item1

我写的如下，但它不起作用

Dim Query

Dim dt As New DataTable

Dim da = New Odbc.OdbcDataAdapter("SELECT * FROM  table1",connection)
da.Fill(dt)

Query = (From row In dt.AsEnumerable Select row_
          Group By item1 = row.Item(6) Into_       
         count = Count(row.Item(6))).ToList

以下行有效：

    Dim q = From p In dt Group p By item = p.Item(6) Into count = Count()

如何将上述查询的结果绑定到GridView？不幸的是，将q设置为DataSource不起作用

    grid.DataSource= q

我发现我应该这样绑定它

    Dim table As DataTable = q.ToDataTable()
    DataGridView1.DataSource = table

但我和这样的错误

    'copytodatatable' is not a member of 'System.Collections.Generic.IEnumerable

这个错误是指什么？

Answer 1

我搜索了几天，终于遇到了由Lus Oliveira编写的这个功能，它将LINQ结果转换为DataTable。（Article）实际功能：

    Public Function EQToDataTable(ByVal parIList As System.Collections.IEnumerable) As System.Data.DataTable
    Dim ret As New System.Data.DataTable()
    Try
        Dim ppi As System.Reflection.PropertyInfo() = Nothing
        If parIList Is Nothing Then Return ret
        For Each itm In parIList
            If ppi Is Nothing Then
                ppi = DirectCast(itm.[GetType](), System.Type).GetProperties()
                For Each pi As System.Reflection.PropertyInfo In ppi
                    Dim colType As System.Type = pi.PropertyType
                    If (colType.IsGenericType) AndAlso
                       (colType.GetGenericTypeDefinition() Is GetType(System.Nullable(Of ))) Then colType = colType.GetGenericArguments()(0)
                    ret.Columns.Add(New System.Data.DataColumn(pi.Name, colType))
                Next
            End If
            Dim dr As System.Data.DataRow = ret.NewRow
            For Each pi As System.Reflection.PropertyInfo In ppi
                dr(pi.Name) = If(pi.GetValue(itm, Nothing) Is Nothing, DBNull.Value, pi.GetValue(itm, Nothing))
            Next
            ret.Rows.Add(dr)
        Next
        For Each c As System.Data.DataColumn In ret.Columns
            c.ColumnName = c.ColumnName.Replace("_", " ")
        Next
    Catch ex As Exception
        ret = New System.Data.DataTable()
    End Try
    Return ret
End Function

它被称为：

dim q = [linq query you  write]
Dim dt as DataTable = EQToDataTable(q)

Answer 2

你的查询正在拉下每条记录...如果你想要计数，你可以做...

select COUNT(*) from Table1

或者，要明确地将结果列命名为计数...

select COUNT(*) as CountOfRecords from Table1

如果你想故意拉下所有记录并知道结果集中有多少实际记录（全表或应用where子句）......你可以从

获得结果

int TotalRecords = dt.Rows.Count

我的坏...按项目分组......

select item, count(*) as TotalPerItem from Table1 group by item

然后，dt.Rows.Count将在列表中返回多少“ITEMS”...然后，您可以滚动每个项目的记录并分别对该项目进行计数。

Answer 3

更改以下行

Dim table As DataTable = q.ToDataTable()

到

Dim table As DataTable = q.ToDataTable().AsEnumerable()

然后你可以尝试将它绑定到GridView

DataGridView1.DataSource = table    
DataGridView1.DataBind()

将LINQ查询结果集转换为DataTable

4 个答案: