基于数据表搭建MCP

本节内容可以参考CaseStudy目录下的文件"MCPServer.foxdb"

在上一节中，我们通过硬编码的方式，手写了两个工具的 JSON 定义。虽然逻辑清晰，但你可能已经发现了一个痛点：JSON 的嵌套结构太长了，手写不仅容易漏掉括号，对于非专业用户来说也极难维护。

既然我们在之前的章节学会了用数据表管理 AI 工具，那么我们同样可以用数据表来管理 MCP 工具。因为 MCP 的 inputSchema 本质上就是标准的 JSON Schema，完全可以用字段来描述。

本节的任务：把 MCP 服务端的工具定义，从代码里彻底抽离到数据表中，实现“零代码”动态生成 MCP 菜单。

本节的MCP服务提供了六个工具，分别用于列出所有表、获取指定表结构、条件计算、分组统计、增加行、获取今天日期。

首先要创建两个表，MCP_Tools 和 MCP_Parameters，分别用于输入工具和工具参数，二者通过 ToolID 关联。

MCP_Tools 表结构:

MCP_Parameters表结构：

AfterOpenProject事件和HttpRequest事件的代码不变，变化的是自定义函数HandleMCP的代码。

自定义函数HandleMCP的代码如下，代码比较长，主要是因为包括了6个工具的执行代码：

Dim e As RequestEventArgs = Args(0)
If String.IsNullOrEmpty(e.PlainText) Then
    Dim emptyErr As New JObject From {{"jsonrpc", "2.0"}, {"id", Nothing}, {"error", New JObject From {{"code", - 32700}, {"message", "Empty request"}}}}
    e.WriteString(emptyErr.ToString(), "application/json")
    Return Nothing
End If

Dim req As JObject = JObject.Parse(e.PlainText)
Dim method As String = If(req("method") IsNot Nothing, req("method").ToString(), "")
Dim id As JToken = req("id")
Dim resp As New JObject From {{"jsonrpc", "2.0"}, {"id", id}}

Try
    Select Case method
        Case "initialize"
            resp("result") = New JObject From {
                {"protocolVersion", "2025-11-25"},
                {"capabilities", New JObject From {{"tools", New JObject()}}},
                {"serverInfo", New JObject From {{"name", "foxDataMcp"}, {"version", "1.0"}}}
            }
        Case "notifications/initialized"
            e.StatusCode = 202
            e.WriteString("", "application/json")
            Return Nothing
        Case "tools/list" '动态读取数据表生成 MCP 菜单
            Dim builder As New AIToolBuilder()
            For Each tr As DataRow In DataTables("MCP_Tools").DataRows
                Dim tool As AITool = builder.AddFunction(tr("ToolName"), tr("Description"))
                For Each pr As DataRow In DataTables("MCP_Parameters").Select("ToolID = " & tr("ToolID"), "SortOrder")
                    Dim EnumValues() As String = Nothing
                    If pr.IsNull("EnumValues") = False Then
                        EnumValues = pr("EnumValues").Split({","c, "，"c})
                    End If
                    tool.AddParameter(pr("ParameterName"), pr("ParameterType"), pr("Description"), pr("IsRequired"), pr("ArrayItemType"), EnumValues)
                Next
            Next
            resp("result") = New JObject From {{"tools", builder.BuildMCP()}} '调用BuildMCP方法生成MCP格式的工具定义
        Case "tools/call" '干活：执行工具
            Dim params As JObject = req("params")
            Dim toolName As String = params("name").ToString()
            Dim toolArgs As JObject = CType(params("arguments"), JObject)
            Dim txt As String = ""
            Dim isError As Boolean = False
            Try
                Select Case toolName
                    Case "compute_table" ' 条件计算
                        Dim tableName As String = toolArgs("table_name").ToString()
                        If DataTables.Contains(tableName) = False Then
                            txt = "{""error"":""表 '" & tableName & "' 不存在""}"
                            isError = True
                        Else
                            Dim expression As String = toolArgs("expression").ToString()
                            Dim filter As String = ""
                            If toolArgs.ContainsKey("filter") Then filter = toolArgs("filter").ToString()
                            Dim dt As DataTable = DataTables(tableName)
                            Dim result As Object = dt.Compute(expression, filter)
                            txt = If(result Is Nothing, "", result.ToString())
                        End If
                    Case "add_row" ' 增加行
                        Dim tableName As String = toolArgs("table_name").ToString()
                        If DataTables.Contains(tableName) = False Then
                            txt = "{""error"":""表 '" & tableName & "' 不存在""}"
                            isError = True
                        Else
                            Dim rowData As JObject = toolArgs("row_data")
                            Dim dt As DataTable = DataTables(tableName)
                            Dim dr As DataRow = dt.AddNew()
                            For Each prop As JProperty In rowData.Properties()
                                Dim colName As String = prop.Name
                                Dim colValue As JToken = prop.Value
                                If dt.DataCols.Contains(colName) Then
                                    dr(colName) = colValue.ToString()
                                End If
                            Next
                            txt = "{""message"":""行已成功添加到表 '" & tableName & "'，请手动保存数据。""}"
                        End If
                    Case "get_today_date"
                        txt = Format(Date.Now, "yyyy-MM-dd")
                    Case "list_tables"
                        Dim nms As New JArray
                        For Each dt As DataTable In DataTables
                            nms.Add(dt.Name)
                        Next
                        txt = nms.ToString()
                    Case "get_table_schema"
                        Dim tableName As String = toolArgs("table_name").ToString()
                        If DataTables.Contains(tableName) = False Then
                            txt = "{""error"":""表 '" & tableName & "' 不存在""}"
                            isError = True
                        Else
                            Dim dt As DataTable = DataTables(tableName)
                            Dim columns As New JArray
                            For Each dc As DataCol In dt.DataCols
                                Dim column As New JObject
                                column("name") = dc.Name
                                column("type") = dc.DataType.Name
                                If dc.Expression > "" Then column("expression") = dc.Expression
                                columns.Add(column)
                            Next
                            txt = columns.ToString()
                        End If
                    Case "group_statistics" ' 分组统计
                        Dim tableName As String = toolArgs("table_name").ToString()
                        If Not DataTables.Contains(tableName) Then
                            txt = "{""error"":""表 '" & tableName & "' 不存在""}"
                            isError = True
                        Else
                            Dim groupCols As JArray = toolArgs("group_columns")
                            Dim aggCols As JArray = toolArgs("aggregates")
                            Dim dt As DataTable = DataTables(tableName)
                            Dim gb As New GroupTableBuilder("临时统计表", dt) 
                            For Each gcol As String In groupCols
                                Dim parts() As String = gcol.Split("|"c)
                                Dim colName As String = parts(0)
                                If dt.DataCols(colName).IsDate Then
                                    Dim groupMode As DateGroupEnum = DateGroupEnum.Month
                                    If parts.Length > 1 Then [Enum].TryParse(Of DateGroupEnum)(parts(1), True, groupMode)
                                    Dim aliasName As String = If(parts.Length > 2, parts(2), "")
                                    gb.Groups.AddDef(colName, groupMode, aliasName)
                                Else
                                    If parts.Length = 1 Then
                                        gb.Groups.AddDef(colName)
                                    ElseIf parts.Length > 1 Then
                                        gb.Groups.AddDef(colName, parts(1))
                                    End If
                                End If
                            Next
                            For Each aggItem As String In aggCols
                                Dim parts() As String = aggItem.Split("|"c)
                                Dim colName As String = parts(0)
                                Dim aggMethod As String = If(parts.Length > 1, parts(1).ToLower(), "sum")
                                Dim aliasName As String = If(parts.Length > 2, parts(2), "")
                                Dim aggType As AggregateEnum = AggregateEnum.Sum
                                If aggMethod > "" Then [Enum].TryParse(Of AggregateEnum)(aggMethod, True, aggType)
                                gb.Totals.AddDef(colName, aggType, aliasName)
                            Next
                            If toolArgs.ContainsKey("filter") Then gb.Filter = toolArgs("filter").ToString()
                            If toolArgs.ContainsKey("same_period_growth") Then gb.SamePeriodGrowth = toolArgs("same_period_growth").ToObject(Of Boolean)()
                            If toolArgs.ContainsKey("circle_growth") Then gb.CircleGrowth = toolArgs("circle_growth").ToObject(Of Boolean)()
                            If toolArgs.ContainsKey("grand_proportion") Then gb.GrandProportion = toolArgs("grand_proportion").ToObject(Of Boolean)()
                            If toolArgs.ContainsKey("group_proportion") Then gb.GroupProportion = toolArgs("group_proportion").ToObject(Of Boolean)()
                            Dim resultTable As DataTable = gb.Build(True)
                            Dim resultJson As New JObject
                            Dim colNames As New JArray
                            For Each dc As DataCol In resultTable.DataCols
                                colNames.Add(dc.Caption)
                            Next
                            resultJson("columns") = colNames
                            Dim rows As New JArray
                            Dim maxRows As Integer = Math.Min(resultTable.dataRows.Count, 1000)
                            For r As Integer = 0 To maxRows - 1
                                Dim dr As DataRow = resultTable.DataRows(r)
                                Dim rowArray As New JArray
                                For Each dc As DataCol In resultTable.DataCols
                                    If dr.IsNull(dc) Then
                                        rowArray.Add(Nothing)
                                    Else
                                        rowArray.Add(dr(dc.Name))
                                    End If
                                Next
                                rows.Add(rowArray)
                            Next
                            resultJson("data") = rows
                            txt = resultJson.ToString()
                        End If
                    Case Else
                        txt = "未知工具：" & toolName
                        isError = True
                End Select
            Catch ex As Exception
                ' 捕获具体工具执行时的报错
                txt = "{""error"":""" & ex.Message & """}"
                isError = True
            End Try
            ' 将执行结果按照 MCP 标准格式包好
            resp("result") = New JObject From {
                {"isError", isError},
                {"content", New JArray From {New JObject From {{"type", "text"}, {"text", txt}}}}
            }
    End Select
Catch ex As Exception
    ' 全局兜底
    resp = New JObject From {{"jsonrpc", "2.0"}, {"id", id}, {"error", New JObject From {{"code", - 32603}, {"message", ex.Message}}}}
End Try
' 输出最终响应
e.WriteString(resp.ToString(), "application/json")

客户端测试代码

现在你可以在客户端项目通过LLMCaller调用这个MCP服务，代码和上一节完全一样，只是系统提示词和提交的问题不同而已。

以下代码请在另一个项目的命令窗口执行：

Dim deepseekKey As String = "sk-a734b83536da45e9aedc3e42605bfb3a" '你的DeepSeek密钥
Dim caller As New LLMCaller("https://api.deepseek.com/chat/completions", "deepseek-chat", deepseekKey)
caller.SystemPrompt = "你是一个数据统计分析专家"
Dim mcpUrl As String = "http://127.0.0.1:18688/mcp"
Dim hc As New HttpClient(mcpUrl)
hc.SkipError = True
hc.ContentType = "application/json"
hc.Headers.Add("Accept", "application/json, text/event-stream")
' 1. 拉取我们自己的工具列表
hc.Content = "{""jsonrpc"":""2.0"",""id"":1,""method"":""tools/list"",""params"":{}}"
Dim listJson As JObject = JsonConvert.DeserializeObject(hc.GetData())
Dim mcpTools As JArray = listJson("result")("tools")
caller.AddMCPTools(mcptools) '将MCP工具注册到LLMCaller
' 2. 设置工具执行器（转发给我们的私有 MCP）
caller.ToolExecutor =
Function(ttoolName As String, targs As JObject) As String
    Dim callReq As New JObject From {
        {"jsonrpc", "2.0"}, {"id", Rand.NextString(10)}, {"method", "tools/call"},
        {"params", New JObject From {{"name", ttoolName}, {"arguments", targs}}}
    }
    hc = hc.Clone
    hc.Content = callReq.ToString()
    Dim respJson As JObject = JsonConvert.DeserializeObject(hc.GetData())
    Return respJson("result")("content")(0)("text").ToString()
End Function
' 3. 让 AI 发起提问
caller.UserMessage = "按年统计产品的销量，并给出同比增长率"
If caller.GetResult() Then
    MessageBoxA.Show(caller.Result)
Else
    MessageBoxA.Show(caller.Error)
End If

将MCP服务连接到智能体软件

同样也可以连接到Trae和WorkBuddy等智能体软件，配置为：

{
    "mcpServers": {
        "foxDataMcp": {
            "url": "http://127.0.0.1:18688/mcp"
        }
    }
}