坑：关于 MySqlClientFactory 没实现 CreateDataAdapter() 方法

情景

在使用数据库通用类 DBHelper 操做 MySql 获取 DataTable 时，DataTable 恒为 null

过程

先看看 DBHelper 获取 DataTable 的代码。

public DataSet ExecuteDataSet(DbCommand cmd)
{
    var dbfactory = DbProviderFactories.GetFactory(DbProviderName);
    var dbDataAdapter = dbfactory.CreateDataAdapter();

    if (dbDataAdapter == null) return null;

    dbDataAdapter.SelectCommand = cmd;
    var ds = new DataSet();
    dbDataAdapter.Fill(ds);
    return ds;
}

源码中使用了 Factory.CreateDataAdapter() 获取 DbDataAdapter，再由 DbDataAdapter 将数据填充到 DataTable，并返回 DataTable。

跟踪 DbFactory 和 DbDataAdapter，发现 DbDataAdapter 为 null。

var factory = DbProviderFactories.GetFactory("MySql.Data.MySqlClient");
var da = factory.CreateDataAdapter();

var f_mysql = MySqlClientFactory.Instance;
var da_mysql = f_mysql.CreateDataAdapter();

额，DbDataAdapter 为 null ？骗人的吧，既然为 null，CreateDataAdapter() 还有啥用？

对比下 CreateDataAdapter() 分别在 Oracle 和 Sqlite 中的状况。

var factory = DbProviderFactories.GetFactory("MySql.Data.MySqlClient");
var da = factory.CreateDataAdapter();

var f_mysql = MySqlClientFactory.Instance;
var f_mssql = SqlClientFactory.Instance;
var f_sqlite = SQLiteFactory.Instance;
var f_oracle = OracleClientFactory.Instance;

var da_mysql = f_mysql.CreateDataAdapter();
var da_mssql = f_mssql.CreateDataAdapter();
var da_sqlite = f_sqlite.CreateDataAdapter();
var da_oracle = f_oracle.CreateDataAdapter();

看看反编译代码，惟独MySQLClientFactory没实现 CreateDataAdapter() 方法

结论

<p style="text-decoration: underline;">MySqlDataAdapter>MySqlDataAdapter 不能由 MySqlClientFactory.CreateDataAdapter() 实例化。</p> 其实只是 config 文件没配置好……

其余

public DataSet ExecuteDataSet(DbCommand cmd)
{
    var dbfactory = DbProviderFactories.GetFactory(DbProviderName);
    var dbDataAdapter = dbfactory.CreateDataAdapter();

    if (dbDataAdapter == null)
    {
        if ("MySql.Data.MySqlClient" == DbProviderName)
        {
            dbDataAdapter = (DbDataAdapter) Assembly.Load("MySql.Data")
                .CreateInstance("MySql.Data.MySqlClient.MySqlDataAdapter");
        }
        else
        {
            return null;
        }
    }

    if (dbDataAdapter == null)
        return null;

    dbDataAdapter.SelectCommand = cmd;
    var ds = new DataSet();
    dbDataAdapter.Fill(ds);
    return ds;
}

参考

• 通用类 DBHelper
• C# CreateDataAdapter 建立 DbDataAdapter，以及用DataTable的Load方法获取数据-布布扣-bubuko.com