坑：关于 MySqlClientFactory 没实现 CreateDataAdapter() 方法-白红宇

坑：关于 MySqlClientFactory 没实现 CreateDataAdapter() 方法

阅读量：6343 次

发布时间：2019-06-22

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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();

输入图片说明

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

唯独MySQLClientFactory没实现

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;}