Dapper：ConnectionString 属性尚未初始化

Question

我第一次玩 Dapper。看起来像一个非常方便的小工具。但是我运行遇到了一个问题。在下面的小控制台应用程序中，第一个方法按预期运行。然而第二种方法returns这个错误：

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll Additional information: The ConnectionString property has not been initialized.

我可以改变方法的顺序并得到相同的结果。我总是在第二次调用时收到错误。不知道我做错了什么。我也试过不使用 db.Close()，但我得到了相同的结果。

无论调用什么方法，错误都在这一行：

db.Open();

有什么想法吗？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;
    }
}

编辑之后：

根据答案，我是这样解决的：

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 的定义移动到方法范围内，那就没问题了。即

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;
    }
}

}

Dapper：ConnectionString 属性尚未初始化

Dapper: The ConnectionString property has not been initialized

.net

c#

sql

dapper

Dapper：ConnectionString 属性 尚未初始化

Dapper: The ConnectionString property has not been initialized

.net

c#

sql

dapper

Dapper：ConnectionString 属性尚未初始化