Dapper：ConnectionString属性尚未初始化

Question

我是第一次与Dapper玩耍。看起来像一个非常方便的小工具。但是我遇到了一个问题。在下面的小型控制台应用程序中，第一种方法按预期运行。但是第二种方法返回此错误：

System.Data.dll中发生了类型为'System.InvalidOperationException'的未处理异常。其他信息：ConnectionString属性尚未初始化。

我可以改变方法的顺序并获得相同的结果。总是在第二次电话上出现错误。不知道我在做什么错。我也尝试不使用db.Close（），但是得到了相同的结果。

无论使用哪种方法调用第二种方法，错误都在这一行：

db.Open();

有任何想法吗？谢谢！

class Program
{
    static IDbConnection db = new SqlConnection(ConfigurationManager.ConnectionStrings["DapperConnection"].ToString());

    static void Main(string[] args)
    {
        IEnumerable<Policy> policy1 = PolicySelectAll();
        IEnumerable<Policy> policy2 = PolicyFindByLastFour("093D");
    }


    public static IEnumerable<Policy> PolicySelectAll()
    {
        var sql = "SELECT * FROM Policy";
        IEnumerable<Policy> policy;
        using (db)
        {
            db.Open();
            policy = db.Query<Policy>(sql);
            db.Close();
        }
        return policy;
    }

    public static IEnumerable<Policy> PolicyFindByLastFour(string LastFour)
    {
        var sql = string.Format("SELECT * FROM Policy WHERE PolicyNumber LIKE '%{0}'", LastFour);
        IEnumerable<Policy> policy;
        using (db)
        {
            db.Open();
            policy = db.Query<Policy>(sql);
            db.Close();
        }
        return policy;
    }
}

编辑后：

根据答案，这是我解决的方法：

class Program
{
    static string connectionString = ConfigurationManager.ConnectionStrings["DapperConnection"].ToString();

    static void Main(string[] args)
    {
        IEnumerable<Policy> policy1 = PolicySelectAll();
        IEnumerable<Policy> policy2 = PolicyFindByLastFour("093D");
    }

    public static IDbConnection GetConnection()
    {
        return new SqlConnection(connectionString);
    }

    public static IEnumerable<Policy> PolicySelectAll()
    {
        IDbConnection db = GetConnection();
        var sql = "SELECT * FROM Policy";
        IEnumerable<Policy> policy;
        using (db)
        {
            db.Open();
            policy = db.Query<Policy>(sql);
            db.Close();
        }
        return policy;
    }

    public static IEnumerable<Policy> PolicyFindByLastFour(string LastFour)
    {
        IDbConnection db = GetConnection();
        var sql = string.Format("SELECT * FROM Policy WHERE PolicyNumber LIKE '%{0}'", LastFour);
        IEnumerable<Policy> policy;
        using (db)
        {
            db.Open();
            policy = db.Query<Policy>(sql);
            db.Close();
        }
        return policy;
    }
}

Answer 1

如果您将 db 的定义移至方法范围内，那就没问题了。IE

class Program
{
    static void Main(string[] args)
    {
        IEnumerable<Policy> policy1 = PolicySelectAll();
        IEnumerable<Policy> policy2 = PolicyFindByLastFour("093D");
    }


    public static IEnumerable<Policy> PolicySelectAll()
    {
        var sql = "SELECT * FROM Policy";
        IEnumerable<Policy> policy;
        using (IDbConnection db = new SqlConnection(ConfigurationManager.ConnectionStrings["DapperConnection"].ToString()))
        {
            db.Open();
            policy = db.Query<Policy>(sql);
            db.Close();
        }
        return policy;
    }

    public static IEnumerable<Policy> PolicyFindByLastFour(string LastFour)
    {
        var sql = string.Format("SELECT * FROM Policy WHERE PolicyNumber LIKE '%{0}'", LastFour);
        IEnumerable<Policy> policy;
        using (IDbConnection db = new SqlConnection(ConfigurationManager.ConnectionStrings["DapperConnection"].ToString()))
        {
            db.Open();
            policy = db.Query<Policy>(sql);
            db.Close();
        }
        return policy;
    }
}

}