Sqlite ExecuteScalar throwing NullReferenceExcpetion
本文关键字:NullReferenceExcpetion throwing ExecuteScalar Sqlite | 更新日期: 2023-09-27 18:35:37
我有一个自定义编写的数据库提供程序。当我运行测试时,它们在 ExecuteScalar
命令上中断并带有NullReferenceException
.我在这里可能错过了什么?我读过有些人有一个多线程问题,但我并不"认为"这就是我遇到的问题。
这是我的 GetOpenConnection 方法
public SqliteConnection GetOpenConnection()
{
var connection = new SqliteConnection(_connectionString);
if (connection == null) throw new Exception("Could not create a database connection.");
connection.Open();
return connection;
}
和 ExecuteScalar 方法
public TKey ExecuteScalar<TKey> ( string commandText, IDictionary<string, object> parameters )
{
using ( var connection = _connectionProvider.GetOpenConnection() )
{
using ( var command = connection.CreateCommand() )
{
command.CommandType = CommandType.Text;
command.CommandText = commandText;
foreach ( var parameter in parameters )
{
command.Parameters.Add( new SqliteParameter( parameter.Key, parameter.Value ?? DBNull.Value ) );
}
// BREAKING HERE
return ( TKey )command.ExecuteScalar();
}
}
}
这就是调用ExecuteScalar
的方法
private const string CheckTableExists = "SELECT name FROM sqlite_master WHERE type='table' AND name='{0}'";
public bool CheckIfTableExists ( string tableName )
{
var exists = ExecuteScalar<int>( string.Format( CheckTableExists, tableName ) ) == 1;
return exists;
}
我在上面放了一个断点,并尝试进入它...代码只是中断并抛出异常...我无法追踪它
如果查询未返回任何记录,则ExecuteScalar
返回 null。这似乎解决了 NullReferenceException。
public TKey ExecuteScalar<TKey> ( string commandText, IDictionary<string, object> parameters )
{
using ( var connection = _connectionProvider.GetOpenConnection() )
{
using ( var command = connection.CreateCommand() )
{
command.CommandType = CommandType.Text;
command.CommandText = commandText;
foreach ( var parameter in parameters )
{
command.Parameters.Add( new SqliteParameter( parameter.Key, parameter.Value ?? DBNull.Value ) );
}
if (typeof (TKey) != typeof (int))
{
return (TKey) command.ExecuteScalar();
}
var executeScalar = command.ExecuteScalar();
var item = executeScalar == null ? 0 : 1;
return (TKey)(object)item;
}
}
}