在集合中找不到参数"param_name" [英] Parameter 'param_name' not found in collection

问题描述

这是我第一次尝试将ADO.NET用于MySQL，但我不知道发生了什么.我一直在尝试定义的第一个参数上收到错误Parameter '_name' not found in collection.

This is my first attempt at using ADO.NET for MySQL, and I have no idea what's going on. I keep getting the error Parameter '_name' not found in collection on the first parameter I try to define.

我已经尝试过重新排序，但是无论我采用哪种方式，MySQL总是会赶上第一行.

I have tried reordering, but no matter which way I put it, MySQL always catches up of the first line.

mySqlCommand = mySqlConnect.CreateCommand();
mySqlCommand.CommandText = "SELECT MajorEquipment.EquipmentNumber, MajorEquipment.EquipmentType, PlantAreaCodes.AreaCode " +
  "FROM MajorEquipment e INNER JOIN PlantAreaCodes a " +
  "ON e.PACId = a.PACId WHERE " +
  "(@EquipmentType IS NULL OR e.EquipmentType = @EquipmentType) " +
  "AND (@EquipmentNumber IS NULL OR e.EquipmentNumber = @EquipmentNumber) " +
  "AND (@AreaCode IS NULL OR a.AreaCode = @AreaCode)";

// The First line shows the error. I have tried @EquipmentType, 
// @EquipmentNumber, and @AreaCode in the first line.

mySqlCommand.Parameters["@EquipmentType"].Value = (string.IsNullOrEmpty(MeModel.EquipmentType) ? (object)DBNull.Value : MeModel.EquipmentType);
mySqlCommand.Parameters["@EquipmentNumber"].Value = (string.IsNullOrEmpty(MeModel.EquipmentNumber) ? (object)DBNull.Value : MeModel.EquipmentNumber);
mySqlCommand.Parameters["@AreaCode"].Value = (string.IsNullOrEmpty(MeModel.Location) ? (object)DBNull.Value : MeModel.Location);

mySqlReader = mySqlCommand.ExecuteReader();

第一个参数显示错误，但是我开始相信这可能与Command字符串有关.

The first parameter shows the error, but I'm starting to believe that it may be something to do with the Command string.

我还尝试用MajorEquipment和AreaCode分别替换e和a.

I have also tried replacing e and a with MajorEquipment and AreaCode respectively.

为什么会这样?

这是我的表格供参考:

+----------------+    +-----------------+
| PlantAreaCodes |    | MajorEquipment  |
|----------------|    |-----------------|
| PACId (PKEY)   |    | MEId (PKEY)     |
| AreaCode       |    | EquipmentType   |
| AreaName       |    | PACId (FKEY)    |
| Comments       |    | EquipmentNumber |
+----------------+    +-----------------+

推荐答案

您需要先将参数添加到集合中，然后再设置其值或使用快捷方式 AddWithValue

You need to add the parameters to the collection before settings their values or use the shortcut AddWithValue

mySqlCommand.Parameters.AddWithValue("@EquipmentType", (string.IsNullOrEmpty(MeModel.EquipmentType) ? (object)DBNull.Value : MeModel.EquipmentType));
mySqlCommand.Parameters.AddWithValue("@EquipmentNumber", (string.IsNullOrEmpty(MeModel.EquipmentNumber) ? (object)DBNull.Value : MeModel.EquipmentNumber));
mySqlCommand.Parameters.AddWithValue("@AreaCode", (string.IsNullOrEmpty(MeModel.Location) ? (object)DBNull.Value : MeModel.Location));

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