在参数化SQL查询中允许Null值

本文关键字：Null 查询 参数 SQL | 更新日期: 2023-09-27 18:11:14

我有以下SQL查询，根据参数将记录插入到数据库中。它工作得很好，但不允许null值，如果有null则返回错误。

表设置为允许null 

SqlConnection dbconnection = new SqlConnection(@"Data Source=LEWIS;Initial Catalog=CustomPC;Integrated Security=True");

SqlCommand InsertPC = new SqlCommand("INSERT INTO [Custom_PC] ([CPU_ID], [Motherboard_ID],[Graphics_Card_ID],[PSU_ID],[RAM_ID],[Case_ID],[Primary_Storage_Drive_ID],[Secondary_Storage_Drive_ID],[Primary_Optical_Drive_ID],[Secondary_Optical_Drive_ID]) VALUES (@CPU_ID, @Motherboard_ID, @Graphics_Card_ID, @PSU_ID, @RAM_ID, @Case_ID, @Primary_Storage_Drive_ID, @Secondary_Storage_Drive_ID, @Primary_Optical_Drive_ID, @Secondary_Optical_Drive_ID) SET @ReturnedID = Scope_Identity();", dbconnection);
SqlParameter CPU_IDParam = InsertPC.Parameters.Add("@CPU_ID", SqlDbType.Int);
CPU_IDParam.Value = Session["DATA"];
SqlParameter Motherboard_IDParam = InsertPC.Parameters.Add("@Motherboard_ID", SqlDbType.Int);
Motherboard_IDParam.Value = Session["MotherboardID"];
SqlParameter Graphics_Card_IDParam = InsertPC.Parameters.Add("@Graphics_Card_ID", SqlDbType.Int);
Graphics_Card_IDParam.Value = Session["GraphicsID"];
SqlParameter PSU_IDParam = InsertPC.Parameters.Add("@PSU_ID", SqlDbType.Int);
PSU_IDParam.Value = Session["PSUID"];
SqlParameter RAM_IDParam = InsertPC.Parameters.Add("@RAM_ID", SqlDbType.Int);
RAM_IDParam.Value = Session["RAMID"];
SqlParameter Case_IDParam = InsertPC.Parameters.Add("@Case_ID", SqlDbType.Int);
Case_IDParam.Value = Session["CaseID"];
SqlParameter Primary_Storage_Drive_IDParam = InsertPC.Parameters.Add("@Primary_Storage_Drive_ID", SqlDbType.Int);
Primary_Storage_Drive_IDParam.Value = Session["HDD1ID"];
SqlParameter Secondary_Storage_Drive_IDParam = InsertPC.Parameters.Add("@Secondary_Storage_Drive_ID", SqlDbType.Int);
Secondary_Storage_Drive_IDParam.Value = Session["HDD2ID"];
SqlParameter Primary_Optical_Drive_IDParam = InsertPC.Parameters.Add("@Primary_Optical_Drive_ID", SqlDbType.Int);
Primary_Optical_Drive_IDParam.Value = Session["OpticalDrive1ID"];
SqlParameter Secondary_Optical_Drive_IDParam = InsertPC.Parameters.Add("@Secondary_Optical_Drive_ID", SqlDbType.Int);
Secondary_Optical_Drive_IDParam.Value = Session["OpticalDrive2ID"];
SqlParameter ReturnedIDParam = InsertPC.Parameters.Add("@ReturnedID", SqlDbType.Int);
ReturnedIDParam.Direction = ParameterDirection.Output;

dbconnection.Open();
InsertPC.ExecuteNonQuery();
Session["PCNum"] = (ReturnedIDParam.Value);
Response.Redirect("~/CustomPC_Details.aspx");

在参数化SQL查询中允许Null值

检查对象是否为null，设置参数为DBNull.Value 

SqlParameter Secondary_Optical_Drive_IDParam = InsertPC.Parameters.Add("@Secondary_Optical_Drive_ID", SqlDbType.Int);
Secondary_Optical_Drive_IDParam.Value = (object)Session["OpticalDrive2ID"] ?? (object)DBNull.Value;

注意，您需要强制转换为object，因为对于??操作符，两个可能的值必须具有相同的类型。

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