基于请求 api 的 C# 过滤器

Question

我正在尝试过滤显示在我的应用程序中的帖子。一切都按预期进行，但我有一个小问题。用户可以选择他所遵循的教育和职业。如何根据获得的数组进行过滤？我试过这样的东西，但感觉很难看。如果我在我的 Filter 类中设置更多的数组，比如 Language[].. 它会变得更加混乱。我可以做点简单的事吗？

public class Filter
{
    public string[] Education { get; set; }

    public string[] Profession { get; set; }
    public int PageIndex { get; set; }

}

示例请求：

public PaginatedResults<Post> FilterPosts(Filter filter)
{

// Both Education and Profession arrays are empty, we just return all the posts
    if(filter.Profession.Any(prof => prof == null) && filter.Education.Any(study => study == null)) {
        var posts1 = _dbContext.Posts.AsEnumerable();
        return _searchService.Pagination<Post>(posts1, filter.PageIndex);
    }
    else 
    {
        // Can this be simplified? Sometimes the Education array is empty and sometimes Profession array. User can choose
        IEnumerable<Post> posts = null;
        if(filter.Profession.Any(prof => prof == null)) 
        {
            posts = _dbContext.Posts.Where(post => filter.Education.Contains(post.Education)).AsEnumerable();
        }
        else if(filter.Education.Any(study => study == null)) 
        {
            posts = _dbContext.Posts.Where(post => filter.Profession.Contains(post.Profession)).AsEnumerable();
        }
        else 
        {
            posts = _dbContext.Posts.Where(post => filter.Profession.Contains(post.Profession) && filter.Education.Contains(post.Education)).AsEnumerable();
        }
        return _searchService.Pagination<Post>(posts, filter.PageIndex);
    }
}

Answer 1

可能有很多方法可以解决这个问题。假设您想保持您的方法（我认为这是完全有效的），您可以尝试以下步骤：

利用IQueryable

假设您使用实体框架，我相信_dbContext.Posts 已经实现了IQueryable。由于 LINQ 不会立即执行，我们可以在枚举集合之前依次构建过滤条件：

posts = _dbContext.Posts.Where(post => filter.Education.Contains(post.Education) && filter.Education.Contains(post.Profession)).AsEnumerable();

// since you are implementing `AND` semantics for your filters, is easy to break down into series of `.Where()` calls
posts = _dbContext.Posts.Where(post => filter.Education.Contains(post.Education))
                        .Where(post => filter.Education.Contains(post.Profession))
                        .AsEnumerable(); // this should filter Posts by Education AND Profession as well as represent the result as IEnumerable. Should be functionally identical to the first statement

反转布尔条件并检查过滤器是否有值

这将允许您仅在需要时添加.Where 过滤器：

if (filter.Profession.Any()) // if Profession has elements
{
    posts = posts.Where(post => filter.Profession.Contains(post.Profession)); // apply respective filter to posts, you may want to ensure you only compare against meaningful search terms by appplying `.Where(i => !string.IsNullOrWhiteSpace(i))` to it
}
if (filter.Education.Any()) // if Education has elements
{
    posts = posts.Where(post => filter.Education.Contains(post.Education)).AsEnumerable(); // apply respective filter to posts          
}

然后，把它们放在一起

public PaginatedResults<Post> FilterPosts(Filter filter)
{
    IQueryable<Post> posts = _dbContext.Posts;
    if (filter.Profession.Any()) posts = posts.Where(post => filter.Profession.Contains(post.Profession));

    if (filter.Education.Any()) posts = posts.Where(post => filter.Education.Contains(post.Education));

    return _searchService.Pagination<Post>(posts.AsEnumerable(), filter.PageIndex); 
}