/// <summary>
/// 从 <see cref="IDbQueryable{TSource}"/> 创建 <see cref="DataSet"/>
/// </summary>
/// <typeparam name="TSource">source 的元素类型</typeparam>
/// <param name="source">查询序列</param>
/// <returns></returns>
public static async Task <DataSet> ToDataSetAsync <TSource>(this IDbQueryable <TSource> source)
{
return(await source.ExecuteAsync <DataSet>());
}
/// <summary>
/// 返回指定序列中满足条件的元素数量
/// </summary>
/// <typeparam name="TSource">source 的元素类型</typeparam>
/// <param name="source">查询序列</param>
/// <param name="predicate">用于测试每个元素是否满足条件的函数</param>
/// <returns></returns>
public static async Task <int> CountAsync <TSource>(this IDbQueryable <TSource> source, Expression <Func <TSource, bool> > predicate)
{
IDbQueryable <int> query = source.CreateQuery <int>(DbExpressionType.Count, predicate);
return(await query.ExecuteAsync <int>());
}
/// <summary>
/// 返回序列中满足指定条件的第一个元素，如果未找到这样的元素，则返回默认值
/// </summary>
/// <typeparam name="TSource">source 的元素类型</typeparam>
/// <param name="source">查询序列</param>
/// <param name="predicate">用于测试每个元素是否满足条件的函数</param>
/// <returns></returns>
public static async Task <TSource> FirstOrDefaultAsync <TSource>(this IDbQueryable <TSource> source, Expression <Func <TSource, bool> > predicate = null)
{
IDbQueryable <TSource> query = source.CreateQuery <TSource>(DbExpressionType.FirstOrDefault, predicate);
return(await query.ExecuteAsync <TSource>());
}
/// <summary>
/// 确定序列是否包含任何元素
/// </summary>
/// <typeparam name="TSource">source 的元素类型</typeparam>
/// <param name="source">查询序列</param>
/// <returns></returns>
/// <param name="predicate">用于测试每个元素是否满足条件的函数</param>
/// <returns>如果源序列中存在元素通过了指定谓词中的测试，则为 true；否则为 false</returns>
public static async Task <bool> AnyAsync <TSource>(this IDbQueryable <TSource> source, Expression <Func <TSource, bool> > predicate)
{
IDbQueryable <bool> query = source.CreateQuery <bool>(DbExpressionType.Any, predicate);
return(await query.ExecuteAsync <bool>());
}