/// <summary>
/// 转换为可分页集合（注：需要对查询接口进行排序操作，否则执行 LINQ 会抛出未排序异常）。
/// </summary>
/// <typeparam name="TEntity">指定的实体类型。</typeparam>
/// <param name="queryable">给定的 <see cref="IQueryable{TEntity}"/>。</param>
/// <param name="computeAction">计算分页的动作。</param>
/// <returns>返回 <see cref="IPageable{TEntity}"/>。</returns>
public static IPageable <TEntity> AsPaging <TEntity>(this IQueryable <TEntity> queryable,
Action <PagingDescriptor> computeAction)
where TEntity : class
{
queryable.NotNull(nameof(queryable));
var descriptor = new PagingDescriptor(queryable.Count());
computeAction?.Invoke(descriptor);
var q = queryable;
// 跳过条数
if (descriptor.Skip > 0)
{
q = q.Skip(descriptor.Skip);
}
// 获取条数
if (descriptor.Size > 0)
{
q = q.Take(descriptor.Size);
}
return(new PagingCollection <TEntity>(q.ToList(), descriptor));
}
private static IPageable <T> AsPaging <T>(this ICollection <T>?rows, Action <PagingDescriptor> computeAction)
where T : class
{
if (rows is null)
{
return(PagingCollection <T> .Empty);
}
var descriptor = new PagingDescriptor(rows.Count);
computeAction?.Invoke(descriptor);
return(new PagingCollection <T>(rows, descriptor));
}
/// <summary>
/// 构造一个 <see cref="PagingCollection{T}"/>。
/// </summary>
/// <param name="rows">给定的行集合。</param>
/// <param name="descriptor">给定的描述符。</param>
public PagingCollection(ICollection <T> rows, PagingDescriptor descriptor)
{
rows.NotNull(nameof(rows));
descriptor.NotNull(nameof(descriptor));
// 如果未进行分页
if (rows.Count > descriptor.Size)
{
// 手动内存分页
_rows = rows
.Skip(descriptor.Skip)
.Take(descriptor.Size)
.ToList();
}
else
{
_rows = rows;
}
Descriptor = descriptor;
}
private PagingCollection()
{
_rows = Array.Empty <T>();
Descriptor = new PagingDescriptor(0);
}