C#使用ADO.Net连接数据库与DbProviderFactory实现多数据库访问

<configuration> 
    <connectionStrings> 
        <add name="default"  connectionString="server=localhost; user id=sa; password=******; database=northwind" 
             providerName="System.Data.SqlClient"/>
    </connectionStrings> 
</configuration>

ConnectionStringSettings settings = ConfigurationManager.ConnectionStrings["default"];
DbProviderFactory provider = DbProviderFactories.GetFactory(settings.ProviderName);

using (DbConnection conn = provider.CreateConnection())
{
    conn.ConnectionString = settings.ConnectionString;
    conn.Open();
    DbCommand cmd = conn.CreateCommand();
    cmd.CommandText = "Select top 10 * From ShortTermBill";
    
    //使用DbDataAdapter
    DbDataAdapter da = provider.CreateDataAdapter();
    da.SelectCommand = cmd;
    DataSet ds = new DataSet();
    da.Fill(ds);
    da.Dispose();
    Console.WriteLine(ds.Tables[0].Rows[0]["BillCode"]);
    
    //使用DbDataReader
    DbDataReader reader = cmd.ExecuteReader()
    while (reader.Read())
    {
        Console.WriteLine(reader.GetString(0));
    }
    conn.Close();
}

class Program
{
    static void Main()
    {
        string connectionString = GetConnectionString();
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            // Connect to the database then retrieve the schema information.  
            connection.Open();string[] columnRestrictions = new String[4];

            // For the array, 0-member represents Catalog; 1-member represents Schema;
            // 2-member represents Table Name; 3-member represents Column Name.
            // Now we specify the Table_Name and Column_Name of the columns what we want to get schema information.
            columnRestrictions[2] = "Device";

            DataTable departmentIDSchemaTable = connection.GetSchema("Columns", columnRestrictions);

            ShowColumns(departmentIDSchemaTable);

        }
    }

    private static string GetConnectionString()
    {
        // To avoid storing the connection string in your code,  
        // you can retrieve it from a configuration file.  
        return "server=10.126.64.1;Database=TPM;user=it;pwd=;ApplicationIntent=ReadOnly;MultiSubnetFailover=True";
    }
    private static void ShowColumns(DataTable columnsTable)
    {
        var selectedRows = from info in columnsTable.AsEnumerable()
                           select new
                           {
                               TableCatalog = info["TABLE_CATALOG"],
                               TableSchema = info["TABLE_SCHEMA"],
                               TableName = info["TABLE_NAME"],
                               ColumnName = info["COLUMN_NAME"],
                               DataType = info["DATA_TYPE"],
                               ORDINAL_POSITION = info["ORDINAL_POSITION"],
                               COLUMN_DEFAULT = info["COLUMN_DEFAULT"],
                               IS_NULLABLE = info["IS_NULLABLE"],
                               CHARACTER_MAXIMUM_LENGTH = info["CHARACTER_MAXIMUM_LENGTH"],
                               NUMERIC_PRECISION = info["NUMERIC_PRECISION"],
                               NUMERIC_SCALE = info["NUMERIC_SCALE"],
                               DATETIME_PRECISION = info["DATETIME_PRECISION"],
                           };

        Console.WriteLine("{0,-15},{1,-15},{2,-15},{3,-15},{4,-15},{5,-15},{6,-15},{7,-15},{8,-15},{9,-15},{10,-15},{11,-15}", "TableCatalog", "TABLE_SCHEMA",
            "表名", "列名", "数据类型", "字段原始顺序", "列默认值", "是否可空", "字符串最大长度", "数字精度", "数字小数点位数", "日期精度"
            );
        foreach (var row in selectedRows)
        {
            Console.WriteLine("{0,-15},{1,-15},{2,-15},{3,-15},{4,-15},{5,-15},{6,-15},{7,-15},{8,-15},{9,-15},{10,-15},{11,-15}", row.TableCatalog,
                row.TableSchema, row.TableName, row.ColumnName, row.DataType, row.ORDINAL_POSITION, row.COLUMN_DEFAULT, row.IS_NULLABLE
                , row.CHARACTER_MAXIMUM_LENGTH, row.NUMERIC_PRECISION, row.NUMERIC_SCALE, row.DATETIME_PRECISION);
        }
    }
}