坑：关于 MySqlClientFactory 没实现 CreateDataAdapter() 方法

情景

在使用数据库通用类 DBHelper 操作 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 中的情况。

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，唯独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……

其他

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 创建 DbDataAdapter，以及用DataTable的Load方法获取数据-布布扣-bubuko.com