从动态文本框中检索动态 sql 参数值的循环问题

Question

全部。我是一个新的 VB.NET 初学者。我面临如何从动态文本框中传递动态 SQL 参数值来搜索数据的问题。我添加了对动态文本框和标签的控制，并希望根据用户输入的动态文本框值搜索数据库表上的数据。目前，我只能从 1 个动态文本框值中搜索数据。

我希望用户输入的动态文本框中的所有值都可以检索，并根据用户输入的SQL参数变量名称和值搜索数据。

有人可以就如何解决这个问题给我一些解决方案吗？我在这个问题上坚持了几天。谢谢大家的帮助！

我尝试过的：

Private Sub FilterData()

    Dim count As Integer = 0

    'filterdata for radiobutton
    Try
        For Each TextBox As TextBox In grp2.Controls.OfType(Of TextBox)()
            For Each Label As Label In grp2.Controls.OfType(Of Label)()

                Using connection As New SqlConnection("connectionString")

                    'user key in the SQL statement
                    sql = TextBox1.Text
                    Dim sql2 As String
                    sql2 = sql
                    Dim sp1 As String() = sql.Split(New String() {"where"}, StringSplitOptions.None)
                    sql = sp1(0) & " where " & Label.Text & " = @parameter or " & Label.Text & " =@parameter"

                    If (TextBox.Text <> "") Then
                        count += 1
                        For j As Integer = 0 To count - 1
                            Using cmd As New SqlCommand(sql, connection)
                                cmd.Parameters.AddWithValue("@parameter", TextBox.Text)
                                'cmd.Parameters.Add("@parameter", SqlDbType.NVarChar, 20).Value = TextBox.Text
                                connection.Open()
                                Dim dt As New DataTable()
                                Dim reader As SqlDataReader
                                reader = cmd.ExecuteReader()
                                dt.Load(reader)
                                DataGridView1.DataSource = dt
                            End Using
                        Next
                    Else
                        GetData()
                    End If
                    'cmd.Dispose()
                    connection.Close()
                End Using
            Next
        Next

    Catch ex As Exception
        'MsgBox(ex.Message)
    End Try

End Sub

Answer 1

首先，如果 Labels 和 TextBoxes 之间存在 1:1 对应关系，那么您不应该使用两个嵌套的 For Each 循环，因为这会将每个 Label 与每个和每个TextBox。您应该做的是创建数组，然后使用单个 For 循环来访问控件对：

Dim labels = grp2.Controls.OfType(Of Label)().ToArray()
Dim textBoxes = grp2.Controls.OfType(Of TextBox)().ToArray()

For i = 0 To labels.getUpperBound(0)
    Dim label = labels(i)
    Dim textBox = textBoxes(i)

    '...
Next

至于构建 SQL 和添加参数，我倾向于这样做：

Dim labels = grp2.Controls.OfType(Of Label)().ToArray()
Dim textBoxes = grp2.Controls.OfType(Of TextBox)().ToArray()
Dim criteria As New List(Of String)
Dim command As New SqlCommand

For i = 0 To labels.getUpperBound(0)
    Dim label = labels(i)
    Dim textBox = textBoxes(i)
    Dim parameterName = "@" & label.Text.Replace(" ", "_")

    criteria.Add($"[{label.Text}] = {parameterName}")
    command.Parameters.AddWithValue(parameterName, textBox.Text)
Next

Dim sql = "SELECT * FROM MyTable"

If criteria.Any() Then
    sql &= " WHERE " & String.Join(" OR ", criteria)
End If

command.CommandText = sql

Answer 2

我认为你应该开始分离 UI 和数据逻辑这里是一个实现的例子：

首先你在数据库中有一个表：

CREATE TABLE Customer (
    Id              INT IDENTITY (1, 1) PRIMARY KEY,
    FirstName       VARCHAR (255) NOT NULL,
    LastName        VARCHAR (255) NOT NULL,
    Phone           VARCHAR (25),
    Email           VARCHAR (255) NOT NULL,
    Street          VARCHAR (255),
    City            VARCHAR (50),
    State           VARCHAR (25),
    ZipCode         VARCHAR (5)
);

然后在 VB 中创建底层实体。网：

Public Class Customer
    Public Property Id As Integer
    Public Property FirstName As String
    Public Property LastName As String
    Public Property Phone As String
    Public Property Email As String
    Public Property Street As String
    Public Property City As String
    Public Property State As String
    Public Property ZipCode As String
End Class

数据加载器

现在您需要一个数据访问组件，将记录加载到上述实体的列表中，这是一个很好的实现：

Imports System.Data.SqlClient

Public Class CustomerDataAccess
    Public Property ConStr As String

    Public Sub New(ByVal constr As String)
        constr = constr
    End Sub

    Public Function GetCustomersByCriterias(constraints As Object) As List(Of Customer)
        Dim query As String = "SELECT Id, FirstName, LastName, Phone, Email, Street, City, State, ZipCode
                             FROM   [dbo].[Customer] "
        Dim result = New List(Of Customer)()

        Using con = New SqlConnection(ConStr)

            Using cmd = con.CreateCommand()
                cmd.CommandType = CommandType.Text
                cmd.CommandText = query

                '' here the magic to add dynamic criteria coming from constraints
                cmd.ApplyConstraints(Of Customer)(constraints)

                con.Open()
                LoadCustomerData(cmd, result)
            End Using
        End Using

        Return result
    End Function

    Private Sub LoadCustomerData(ByVal cmd As SqlCommand, ByVal result As List(Of Customer))
        Using rdr = cmd.ExecuteReader()
            Dim idIdx As Integer = rdr.GetOrdinal("Id")
            Dim firstNameIdx As Integer = rdr.GetOrdinal("FirstName")
            Dim lastNameIdx As Integer = rdr.GetOrdinal("LastName")
            Dim phoneIdx As Integer = rdr.GetOrdinal("Phone")
            Dim emailIdx As Integer = rdr.GetOrdinal("Email")
            Dim streetIdx As Integer = rdr.GetOrdinal("Street")
            Dim cityIdx As Integer = rdr.GetOrdinal("City")
            Dim stateIdx As Integer = rdr.GetOrdinal("State")
            Dim zipCodeIdx As Integer = rdr.GetOrdinal("ZipCode")

            While rdr.Read()
                Dim item = New Customer()
                item.Id = rdr.GetValueOrDefault(Of Integer)(idIdx)
                item.FirstName = rdr.GetValueOrDefault(Of String)(firstNameIdx)
                item.LastName = rdr.GetValueOrDefault(Of String)(lastNameIdx)
                item.Phone = rdr.GetValueOrDefault(Of String)(phoneIdx)
                item.Email = rdr.GetValueOrDefault(Of String)(emailIdx)
                item.Street = rdr.GetValueOrDefault(Of String)(streetIdx)
                item.City = rdr.GetValueOrDefault(Of String)(cityIdx)
                item.State = rdr.GetValueOrDefault(Of String)(stateIdx)
                item.ZipCode = rdr.GetValueOrDefault(Of String)(zipCodeIdx)
                result.Add(item)
            End While
        End Using
    End Sub
End Class

扩展方法

以下是上面引用的扩展方法，它们可以发挥您正在寻找的魔力：

DataReader 扩展，使用 Dbnull 特殊大小写和强制转换可以轻松地从 SalDataReader 读取值

Module DataReaderExtenions
    <Extension()>
    Function GetValueOrDefault(Of T)(row As IDataRecord, fieldName As String) As T
        Dim ordinal = row.GetOrdinal(fieldName)
        Return row.GetValueOrDefault(Of T)(ordinal)
    End Function

    <Extension()>
    Function GetValueOrDefault(Of T)(row As IDataRecord, ordinal As Integer) As T
        Return (If(row.IsDBNull(ordinal), Nothing, row.GetValue(ordinal)))
    End Function

    <Extension()>
    Function GetValueOrDefaultSqlite(Of T)(row As IDataRecord, fieldName As String) As T
        Dim ordinal = row.GetOrdinal(fieldName)
        Return row.GetValueOrDefault(Of T)(ordinal)
    End Function

    <Extension()>
    Function GetValueOrDefaultSqlite(Of T)(row As IDataRecord, ordinal As Integer) As T
        Return (If(row.IsDBNull(ordinal), Nothing, Convert.ChangeType(row.GetValue(ordinal), GetType(T))))
    End Function
End Module

可让您从匿名对象值中提取标准的命令扩展：

Imports System.Reflection
Imports System.Runtime.CompilerServices


Module CommandExtensions
    <Extension()>
    Function AddParameter(command As IDbCommand, name As String, value As Object) As IDataParameter
        If command Is Nothing Then Throw New ArgumentNullException("command")
        If name Is Nothing Then Throw New ArgumentNullException("name")
        Dim p = command.CreateParameter()
        p.ParameterName = name
        p.Value = If(value, DBNull.Value)
        command.Parameters.Add(p)
        Return p
    End Function

    <Extension()>
    Function ToDictionary(data As Object) As Dictionary(Of String, Object)
        If TypeOf data Is String OrElse data.[GetType]().IsPrimitive Then Return New Dictionary(Of String, Object)()
        Return (From [property] In data.[GetType]().GetProperties(BindingFlags.[Public] Or BindingFlags.Instance)
                Where [property].CanRead
                Select [property]).ToDictionary(Function([property]) [property].Name, Function([property]) [property].GetValue(data, Nothing))
    End Function

    <Extension()>
    Sub ApplyConstraints(Of TEntity)(cmd As IDbCommand, constraints As Object)
        If constraints Is Nothing Then Return
        Dim dictionary = constraints.ToDictionary()
        Dim whereClause = " WHERE "

        For Each kvp In dictionary
            Dim columnName = kvp.Key
            Dim propertyName = kvp.Key
            Dim prefix = "@"c
            Dim value = kvp.Value
            whereClause += $"{columnName} **like** {prefix}{propertyName} AND "
            cmd.AddParameter(propertyName, value)
        Next

        If String.IsNullOrEmpty(whereClause) Then Return
        cmd.CommandText += whereClause.Remove(whereClause.Length - 5, 5)
    End Sub
End Module

示例：

编码完所有这些内容后，您现在可以执行以下操作：

Dim DataGridView1 As DataGridView = New DataGridView()
Dim ConStr As String = ConfigurationManager.ConnectionStrings("MyApp").ConnectionString
Dim dal As CustomerDataAccess = New CustomerDataAccess(ConStr)
Dim criterias = New With {.FirstName = "%James%", .LastName = "%Nadin%"}
DataGridView1.DataSource = dal.GetCustomersByCriterias(criterias)

尽管有所有这些代码，您仍然需要将您的文本框（在正确命名它们之后）绑定到 SearchEntity 并使用该实体来提供条件

我希望本材料可以帮助您解决问题并激励您提高架构和开发技能