如果列表为空，则返回与所有提供的参数匹配的记录

Question

我想按过滤列表条件搜索列表。

例如，我将contact_id、姓名、州和城市列表作为字符串列表。

public async Task<List<ContactRequestListModel>> SearchByMultipleAsync(
    List<string> contact_id, 
    List<string> email,
    List<string> phone, 
    List<string> name, 
    List<string> accountnumber, 
    List<string> city, 
    List<string> state)
{


var line = (from x in filtered
            where city.Contains(x.City)
         || contact_id.Contains(x.Id.ToString())
         || state.Contains(x.State)
         || name.Contains(x.FirstName + " " + x.MiddleName ?? "" + " " + x.LastName) select x).ToList();

return line;
}

上述 LINQ 查询返回与传递的任何参数匹配的所有记录。它还返回 city 和 states 匹配但没有匹配 contact_id 的记录

如何搜索与所有提供的参数匹配的记录，如果提供的参数列表为空或未找到，则应跳过搜索。

Answer 1

最好通过过滤器的存在来过滤：

    public class ContactRequestSearchRequest
    {
        public List<string> ContactIds { get; set; }
        public List<string> Emails { get; set; }
        public List<string> Phones { get; set; }
        public List<string> Names { get; set; }
        public List<string> AccountNumbers { get; set; }
        public List<string> Cities { get; set; }
        public List<string> States { get; set; }
    }

    public static async Task<List<ContactRequestListModel>> SearchAsync(ContactRequestSearchRequest request, CancellationToken cancellationToken = default)
    {
        var query = filtered.AsQueryable();
        if (request.ContactIds != null)
            query = query.Where(x => request.ContactIds.Contains(x.Id));
        if (request.Emails != null)
            query = query.Where(x => request.Emails.Contains(x.mail.address));

        //all other filterings...

        if (request.Names != null)
            query = query.Where(x => request.Names.Contains(x.FirstName + " " + x.MiddleName ?? "" + " " + x.LastName));

        return await query.ToListAsync(cancellationToken).ConfigureAwait(false);
    }

这有两个原因：

• 如您所见，它们是相似的，以后如果替换属性，将很容易重构为常用方法，例如FilterBy

• EF 查询是愚蠢的，如果你在其中包含一些东西，它仍然会产生像1=1 这样的垃圾，从而扼杀查询计划和性能。因此，最好在添加要查询的内容之前检查代码。

考虑您的用例

假设如果我尝试使用州、城市进行过滤并且没有通过名称，则返回的列表将为空

不清楚您想要什么，如果您的任何过滤器为空/空，则不返回任何内容 - 然后只需在函数开头检查它：

        if (request.ContactIds == null && !request.ContactIds.Any() || 
            request.Emails == null || !request.Emails.Any() ||
            ...)
            return new List<ContactRequestListModel>();

Answer 2

我建议是这样的：

var line = filtered
  .Where(x => (city?.Count ?? 0) <= 0 || city.Contains(x.City))
  .Where(x => (state?.Count ?? 0) <= 0 || state.Contains(x.State))
  .Where(x => (name?.Count ?? 0) <= 0 || name.Contains($"{x.FirstName} {x.MiddleName} {x.LastName}"))
  .ToList();

具有典型的模式

x => (city?.Count ?? 0) <= 0 || city.Contains(x.City)

如果city 为空或为空，我们跳过city 过滤，否则我们需要匹配。您可以根据需要添加任意数量的Where（每个列表一个用于比较）。

对于name 过滤，我保留了您当前的实现，但请注意，如果记录没有 MiddleName 组合名称将有双空间：

John  Smith  

要摆脱双空格，您可以加入不为空的名称：

string.Join(" ", new string[] {
   x.FirstName, x.MiddleName, x.LastName}
  .Where(s => !string.IsNullOrEmpty(s))) 

即

.Where(x => (name?.Count ?? 0) <= 0 ||
   name.Contains(string.Join(" ", new string[] {
     x.FirstName, x.MiddleName, x.LastName}
    .Where(s => !string.IsNullOrEmpty(s)))
 ));

Answer 3

使用 and (&&) 代替 or (||)

var line = (from x in filtered
            where city.Contains(x.City)
         && contact_id.Contains(x.Id.ToString())
         && state.Contains(x.State)
         && name.Contains(x.FirstName + " " + x.MiddleName ?? "" + " " + x.LastName) select x).ToList();

if (line == null)
    //do what you want
else
    return line;

Answer 4

试试这个

var line = (from x in filtered
            where (!city.Any() || city.Contains(x.City))
            && (!contact_id.Any() || contact_id.Contains(x.Id.ToString()))
            && (!state.Any() || state.Contains(x.State))
            && name.Contains(x.FirstName + " " + x.MiddleName ?? "" + " " + x.LastName) 
            select x).ToList();

return line;