数据库访问的抽象层

Question

我想为mysql和mssql编写自定义SQL代码(可能更晚些时候).

var dbSystem = "mssql";
if ("mssql" == dbSystem) {
    var mssqlConn = new SqlConnection(mssqlConnString);
    new SqlCommand("CREATE TABLE t1 (c1 in NOT NULL PRIMARY KEY IDENTITY(1,1), c2 int)", mssqlConn).ExecuteNonQuery();
} else {
    var mysqlConn = new MySqlConnection(mysqlConnString);
    new SqlCommand("CREATE TABLE t1 (c1 in NOT NULL AUTO_INCREMENT PRIMARY KEY, c2 int)", mssqlConn).ExecuteNonQuery();
}

问题从这里开始.我想在if语句之前通过接口或abstract-class声明连接.但似乎不可能,因为命令类明确要求特定的SqlConnection或MySqlConnection.

如果你想执行一个简单的命令,问题就会变得更糟SELECT c1 form t1 where c2 = @value.因为你必须像上面那样做.

是否有API为这样的工作流程提供服务:

IDbConnection conn; // initialized by SqlConnection or MySqlConnection, etc.
IDbCommand cmd = new DbCommand("SELECT c1 form t1 where c2 = @value", conn);
cmd.Parameters.Add("@value", Type.Int);

问题:

• System.Data.Common.DbCommand是一个抽象类
• SqlDbCommand(MySqlDbCommand等)要求有特定的连接
• DbCommand.Properties不支持"添加"两个参数("@ placeholer",value),如SqlDbCommand的属性
• 我不需要/想要一个完整的ORM; 只是现有异构API上的接口/抽象层

Answer 1

要走的路是使用DbProviderFactories.GetFactory(String)来检索DbProviderFactory对象.

使用DbProviderFactory.CreateConnection()会给你一个DbConnection对象.

设置此DbConnection对象的ConnectionString属性并调用Open()方法将导致打开与所需数据库的连接.

使用DbConnection.CreateCommand()将为您提供一个可以根据需要使用的DbCommand对象.

对于使用参数化查询,您可以使用DbCommand.CreateParameter()来返回DbParameter对象.

样品:

// MySQL
DbProviderFactory factory = DbProviderFactories.GetFactory("MySql.Data.MySqlClient"); 

// MS-SQL
DbProviderFactory factory = DbProviderFactories.GetFactory("System.Data.SqlClient");  

private void Query(String query,Dictionary<String,object> namesAndValues, System.Data.CommandType commandType)
{
    String connectionString = ConfigurationManager.ConnectionStrings["yourConnectionString"];

    using (DbConnection connection = factory.CreateConnection())
    {
        connection.ConnectionString = connectionString;
        connection.Open();
        using (DbCommand command = connection.CreateCommand())
        {
            command.CommandText = query;
            command.CommandType = commandType;
            AddParameters(command, namesAndValues);
            using (DbDataReader reader=command.ExecuteReader())
            {
                while (reader.Read())
                {
                 //
                }
            }
         }
    }

}
private void AddParameters(DbCommand command, Dictionary<String, object> namesAndValues)
{
    String factoryName = factory.GetType().Name;
    DbParameter para;
    foreach (String key in namesAndValues.Keys)
    {
        para = command.CreateParameter();
        switch (factoryName)
        {
            case "SqlClientFactory":
                para.ParameterName = "@" + key;
                break;
             case "OracleClientFactory":
                para.ParameterName = ":" + key;
                break;
            case "OleDbFactory":
                para.ParameterName = "?";
                break;
            case "MySqlClientFactory":
                para.ParameterName = "?" + key;
                break;
        }
        para.Value = namesAndValues[key];
        command.Parameters.Add(para);

    }
}