EF6 从 MySQL 表中选择

Question

我有一个现有的带有表的 MySQL 数据库。我正在创建一个 Windows 服务，它将从 MySql 表 c2b2_callbacks 中获取数据并将值传递给我的 DTO 类。

下面是我的选择语句

public async Task<IEnumerable<Callback>> GetCallbacks()
    {

        using(MySqlConnection conn = new MySqlConnection(connectionString))
        {
            try
            {
                await conn.OpenAsync();
                //MySqlTransaction sqlTransaction = await conn.BeginTransactionAsync();

                using (M2AContext context = new M2AContext())
                {
                    //context.Database.UseTransaction(sqlTransaction);

                    // Error
                    IEnumerable<CallBack> transactions = await context.Transactions.SqlQuery("SELECT * FROM oapi_test.c2b2_callbacks WHERE Status = 0 AND MSISDN REGEXP \'^([a-z]*[a-z]\\s*){3}([0-9]*[0-9]){3}([a-z]){1}$\';").ToListAsync(); 
                    return transactions;
                }
            }
            catch(Exception e)
            {
                //log
                Console.WriteLine($"Error {e.Message}");
                return null;
            }
        }
    }

下面是我的CallBack类

 public class CallBack
{
    public string TransID { get; set; }
    public DateTime TransTime { get; set; }
    public string MSISDN { get; set; }

    public Int16 Status { get; set; }
}

以下是我的上下文

[DbConfigurationType(typeof(MySqlEFConfiguration))]
public class M2AContext: DbContext
{
    public M2AContext(): base()
    {

    }

    public M2AContext(DbConnection connection, bool ownedconnection): base(connection, ownedconnection)
    {

    }

    public DbSet<Callbacks> Transactions { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
    }
}

我正在尝试获取交易，但它在SELECT 语句中失败并抛出此错误

{"Object reference not set to an instance of an object."}  

我浏览了this 文档，但我不知道为什么会出现这个错误。

这是堆栈跟踪

at MySql.Data.MySqlClient.MySqlProviderServices.GetDbProviderManifestToken(DbConnection connection)
at System.Data.Entity.Core.Common.DbProviderServices.GetProviderManifestToken(DbConnection connection)
at MySql.Data.Entity.MySqlManifestTokenResolver.ResolveManifestToken(DbConnection connection)
at System.Data.Entity.Utilities.DbConnectionExtensions.GetProviderInfo(DbConnection connection, DbProviderManifest& providerManifest)
at System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection)
at System.Data.Entity.Internal.LazyInternalContext.CreateModel(LazyInternalContext internalContext)
at System.Data.Entity.Internal.RetryLazy`2.GetValue(TInput input)
at System.Data.Entity.Internal.LazyInternalContext.InitializeContext()
at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType)
at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize()
at System.Data.Entity.Internal.Linq.InternalSet`1.get_InternalContext()
at System.Data.Entity.Internal.Linq.InternalSet`1.ExecuteSqlQueryAsync(String sql, Boolean asNoTracking, Nullable`1 streaming, Object[] parameters)
at System.Data.Entity.Internal.InternalSqlSetQuery.GetAsyncEnumerator()
at System.Data.Entity.Infrastructure.DbRawSqlQuery`1.System.Data.Entity.Infrastructure.IDbAsyncEnumerable<TElement>.GetAsyncEnumerator()
at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.ForEachAsync[T](IDbAsyncEnumerable`1 source, Action`1 action, CancellationToken cancellationToken)
at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.ToListAsync[T](IDbAsyncEnumerable`1 source, CancellationToken cancellationToken)
at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.ToListAsync[T](IDbAsyncEnumerable`1 source)
at System.Data.Entity.Infrastructure.DbRawSqlQuery`1.ToListAsync()
at m2a.Repositories.Repository.<GetCallbacks>d__2.MoveNext() in C:\Users\JNyingi\source\repos\m2a\Repositories\Repository.cs:line 38

Answer 1

我认为您需要提供一个映射，否则 EF 将不知道如何绑定到 CallBack 对象

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
    }

应该是

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<CallBack>("c2b2_callbacks");
    }