我正在编写一个 C# 应用程序，使用 Dapper for ORM 从 MySQL 数据库检索菜谱。到目前为止，我已经用 C# 使用直接查询编写了 DAL（我知道这是不安全的），而且效果很好。我现在开始过渡到带有参数的存储过程，以更好地保护数据库免受 SQL 注入，并尽可能使用最佳实践。
然而，当我使用 Dapper 时QueryAsync<T>（这也适用于Query<T>） 随着DynamicParameters，我收到异常，并显示消息“数据为空。无法对空值调用此方法或属性。”
但是，如果我将查询作为字符串文字 SQL 语句执行，或者使用字符串文字调用存储过程，则它可以正常工作。我知道数据在那里，并且不为空，因为当使用我知道存在的一组 id 号直接在 MySQL 中运行它时它可以工作。我还尝试使用我知道存在的 id 在 C# 中运行下面列出的方法，其中一些工作正常，其中一些返回所述错误。
一旦我做了，我不知道这是哪里失败了QueryAsync<Recipe>("...")称呼。我不知道我提供给该方法的参数是否未传递到存储过程中，或者该过程是否返回 null，或者如果出现错误则出现其他情况。
任何有关解决该调用可能失败的问题的帮助将不胜感激。
我已经在底部添加了堆栈跟踪，但我还无法理解它。我仍然需要学习理解堆栈跟踪。
Edit:我在 SQL Server 中重新创建了 MySql 数据库，并创建了一个新的 DAL 连接器。所有这些都完全反映了 MySql 结构和 DAL。GetRecipeByIdAsync1(int id)与 SQL Server 完全按照预期工作。因此，Dapper/DynamicParameters/MySql.Data 与 MySQL 中的存储过程交互的方式一定有问题
我的食谱课：
public class Recipe
{
[Description("id")]
public int Id { get; set; }
[Description("name")]
public string Title { get; set; }
[Description("description")]
public string Description { get; set; }
[Description("source_site")]
public string SourceSite { get; set; }
}
这是我的recipesMySQL 中的表：
recipes
=============
id (pk) | INT | Not Null | Auto-Increment
name | VARCHAR(45) | Not Null |
description | VARCHAR(250) | Allow Null |
source_site | VARCAHR(200) | Allow Null |
这是我用来设置自定义映射的帮助程序类，因此我的列不需要匹配属性名称：
public class Helper
{
public static void SetTypeMaps()
{
var recipeMap = new CustomPropertyTypeMap(typeof(Recipe),
(type, columnName) => type.GetProperties().FirstOrDefault(prop => GetDescriptionFromAttribute(prop) == columnName));
SqlMapper.SetTypeMap(typeof(Recipe), recipeMap);
// Other custom mappers omitted
}
我正在使用的存储过程：
PROCEDURE `sp_recipes_GetByRecipeId`(IN RecipeId INT)
BEGIN
SELECT r.*
FROM recipes r
WHERE r.id = RecipeId;
END
现在介绍我在 DAL 中使用的方法的各个版本（为了方便起见，我在这里对它们进行了编号）：
/// This does not work
public async Task<Recipe> GetRecipeByIdAsync1(int id)
{
using (IDbConnection db = new MySqlConnection(GlobalConfig.CnnString("CookbookTest1")))
{
var p = new DynamicParameters();
p.Add("RecipeId", id, dbType: DbType.Int32, direction: ParameterDirection.Input);
// This is the line where the exception occurs
var result = await db.QueryAsync<Recipe>("sp_recipes_GetByRecipeId", p, commandType: CommandType.StoredProcedure);
return result.FirstOrDefault();
}
}
// This also does not work
public async Task<Recipe> GetRecipeByIdAsync2(int id)
{
using (IDbConnection db = new MySqlConnection(GlobalConfig.CnnString("CookbookTest1")))
{
// This is the line where the exception occurs
var result = await db.QueryAsync<Recipe>("sp_recipes_GetByRecipeId", new {RecipeID = id}, commandType: CommandType.StoredProcedure);
return result.FirstOrDefault();
}
}
// Nor this
public async Task<Recipe> GetRecipeByIdAsync3(int id)
{
using (IDbConnection db = new MySqlConnection(GlobalConfig.CnnString("CookbookTest1")))
{
// This is the line where the exception occurs
var result = await db.QueryAsync<Recipe>("sp_recipes_GetByRecipeId", new {id}, commandType: CommandType.StoredProcedure);
return result.FirstOrDefault();
}
}
// This works perfectly, but I'm not sure how safe it is
public async Task<Recipe> GetRecipeByIdAsync4(int id)
{
using (IDbConnection db = new MySqlConnection(GlobalConfig.CnnString("CookbookTest1")))
{
var result = await db.QueryAsync<Recipe>($"call sp_recipes_GetByRecipeId({id})");
return result.FirstOrDefault();
}
}
// And of course, this works, but is horrible practice
public async Task<Recipe> GetRecipeByIdAsync5(int id)
{
using (IDbConnection db = new MySqlConnection(GlobalConfig.CnnString("CookbookTest1")))
{
var result = await db.QueryAsync<Recipe>($"SELECT * FROM recipes WHERE recipes.id = {id}");
return result.FirstOrDefault();
}
}
连接字符串（如果有人想要）
<connectionStrings>
<add name="CookbookTest1" connectionString="Server=localhost;Database=cookbook_test1;Uid=vs_dev;Pwd=developer;" providerName="MySql.Data"/>
</connectionStrings>
堆栈跟踪：
System.Data.SqlTypes.SqlNullValueException
HResult=0x80131931
Message=Data is Null. This method or property cannot be called on Null values.
Source=MySql.Data
StackTrace:
at MySql.Data.MySqlClient.MySqlDataReader.GetFieldValue(Int32 index, Boolean checkNull)
at MySql.Data.MySqlClient.MySqlDataReader.GetString(Int32 i)
at MySql.Data.MySqlClient.MySqlDataReader.GetString(String column)
at MySql.Data.MySqlClient.SchemaProvider.GetProcedures(String[] restrictions)
at MySql.Data.MySqlClient.ISSchemaProvider.GetProcedures(String[] restrictions)
at MySql.Data.MySqlClient.ISSchemaProvider.GetSchemaInternal(String collection, String[] restrictions)
at MySql.Data.MySqlClient.SchemaProvider.GetSchema(String collection, String[] restrictions)
at MySql.Data.MySqlClient.MySqlConnection.GetSchemaCollection(String collectionName, String[] restrictionValues)
at MySql.Data.MySqlClient.ProcedureCache.GetProcData(MySqlConnection connection, String spName)
at MySql.Data.MySqlClient.ProcedureCache.AddNew(MySqlConnection connection, String spName)
at MySql.Data.MySqlClient.ProcedureCache.GetProcedure(MySqlConnection conn, String spName, String cacheKey)
at MySql.Data.MySqlClient.StoredProcedure.GetParameters(String procName)
at MySql.Data.MySqlClient.StoredProcedure.CheckParameters(String spName)
at MySql.Data.MySqlClient.StoredProcedure.Resolve(Boolean preparing)
at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior)
at MySql.Data.MySqlClient.MySqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
at System.Data.Common.DbCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
at Dapper.SqlMapper.<QueryAsync>d__33`1.MoveNext() in C:\projects\dapper\Dapper\SqlMapper.Async.cs:line 468
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at CookbookLibrary.DataAccess.MySqlConnector.<TestStoredProcAsync>d__5.MoveNext() in C:\Users\cyclone\Desktop\VS Projects\DigitalCookbook\CookbookLibrary\DataAccess\MySqlConnector.cs:line 119
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at DigitalCookbook.ViewModel.MainWindowModel.<TestProcedure>d__38.MoveNext() in C:\Users\cyclone\Desktop\VS Projects\DigitalCookbook\DigitalCookbook\ViewModel\MainWindowModel.cs:line 228
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
at DigitalCookbook.ViewModel.MainWindowModel.<<get_TestCommand>b__31_0>d.MoveNext() in C:\Users\cyclone\Desktop\VS Projects\DigitalCookbook\DigitalCookbook\ViewModel\MainWindowModel.cs:line 114
