使用LINQ . select()转换为新类型太慢了

本文关键字：类型 LINQ select 转换 使用 新类型 | 更新日期: 2023-09-27 18:05:35

当前项目，打破了这个问题:

客户端存储库:

public class ClientRepository
{
    // Members
    private masterDataContext _db;
    // Constructor
    public ClientRepository()
    {
        _db = new masterDataContext();
    }
    public IEnumerable<ClientName> GetCorporateClientNames()
    {
        return _db.corporate_client_tbs.Select(o => new ClientName { id = o.id, name = o.company_name }).AsEnumerable();
    }
    public IEnumerable<ClientName> GetRetailClientNames()
    {
        return _db.retail_client_tbs.Select(o => new ClientName { id = o.id, name = o.name }).AsEnumerable();
    }
    // Define return type
    public class ClientName
    {
        public int id { get; set; }
        public string name { get; set; }
    }
}

现在在控制器中我有以下内容:

public ActionResult Index()
{
    var _visits = _db.GetAllServiceVisits();
    return View(_visits);
}

加载当前存在的200行奇数行的视图大约需要4秒。

我想添加一个属性"client"到包含客户端名称的访问模型。客户端的名称将来自两个不同的表中的一个，该表是从两个类型为"ClientName"的数组中的一个中获取的。

这是第一种方法，使用LINQ:

public ActionResult Index()
{
    private ClientRepository _cr = new ClientRepository();
    var _retailclients = _cr.GetRetailClientNames().ToArray();
    var _corporateclients = _cr.GetCorporateClientNames().ToArray();
    var _visits = _db.GetAllServiceVisits();
    var _temp = _visits.Select(o => new ServiceVisitViewModel
        {
            service_visit = o,
            client = (o.client_type ? _corporateclients.Where(p => p.id == o.client_id).First().name : _retailclients.Where(p => p.id == o.client_id).First().name)
        }).ToArray();
    return View(_temp);
}

这是第二种方法，使用普通的c#:

public ActionResult Index()
{
    private ClientRepository _cr = new ClientRepository();
    var _retailclients = _cr.GetRetailClientNames().ToArray();
    var _corporateclients = _cr.GetCorporateClientNames().ToArray();
    var _visits = _db.GetAllServiceVisits();
    List<ServiceVisitViewModel> _temp = new List<ServiceVisitViewModel>();
    foreach (service_visit_tb v in _visits)
    {
        _temp.Add(new ServiceVisitViewModel { service_visit = v, client = (v.client_type ? _corporateclients.Where(p => p.id == v.client_id).First().name : _retailclients.Where(p => p.id == v.client_id).First().name) });
    }
    return View(_temp);
}

根据我的测试，第二种方法大约快8 - 10倍。

我能看到的唯一区别是。select语句。

有人能告诉我，如果我在第一种方法或替代方法中做错了什么，为什么第一种方法如此!@#$ing缓慢?

编辑:_db.GetAllServiceVisits()定义如下:

public IEnumerable<service_visit_tb> GetAllServiceVisits()
{
    var _visits = _db.service_visit_tbs;
    return _visits.AsEnumerable();
}

结束编辑

第二个编辑:我已经从日志中的每个条目中删除了这一行:

-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 4.0.30319.1

上下文日志如下:

// This query is to fetch all the clients of Type One (corresponding to _cr.GetRetailClientNames() )
SELECT [t0].[id], [t0].[name]
FROM [genii].[retail_client_tb] AS [t0]
// This query is to fetch all the clients of Type Two (corresponding to _cr.GetCorporateClientNames() )
SELECT [t0].[id], [t0].[company_name] AS [name]
FROM [genii].[corporate_client_tb] AS [t0]
// This is the main query (loading roughly 250 records) which fetchs all Visits
SELECT [t0].[id], [t0].[client_type], [t0].[client_id], [t0].[machine_type], [t0].[machineID], [t0].[visit_type], [t0].[scheduledon], [t0].[arrivedon], [t0].[completedon], [t0].[reported_problem], [t0].[diagnosed_problem], [t0].[action_taken], [t0].[visit_status], [t0].[engineer_id], [t0].[reference_id], [t0].[addedby], [t0].[addedon], [t0].[modifiedby], [t0].[modifiedon]
FROM [genii].[service_visit_tb] AS [t0]
// These next queries are not being manually called by me, I assume they are being
// called when the Razor view is compiled since I am calling the name value of a linked table as such:
// @item.service_visit.engineer_tb.name
SELECT [t0].[id], [t0].[type]
FROM [genii].[visit_type_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [8]
SELECT [t0].[id], [t0].[status]
FROM [genii].[visit_status_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [1]
SELECT [t0].[id], [t0].[name]
FROM [genii].[engineer_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [3]
SELECT [t0].[id], [t0].[type]
FROM [genii].[visit_type_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [11]
SELECT [t0].[id], [t0].[name]
FROM [genii].[engineer_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [2]
SELECT [t0].[id], [t0].[type]
FROM [genii].[visit_type_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [7]
SELECT [t0].[id], [t0].[type]
FROM [genii].[visit_type_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [2]
SELECT [t0].[id], [t0].[type]
FROM [genii].[visit_type_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [6]
SELECT [t0].[id], [t0].[type]
FROM [genii].[visit_type_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [3]
SELECT [t0].[id], [t0].[name]
FROM [genii].[engineer_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [5]
SELECT [t0].[id], [t0].[name]
FROM [genii].[engineer_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [4]
SELECT [t0].[id], [t0].[status]
FROM [genii].[visit_status_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [8]
SELECT [t0].[id], [t0].[status]
FROM [genii].[visit_status_tb] AS [t0]
WHERE [t0].[id] = @p0
-- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [2]

问题的附录:是否有更好的方法来提取这些数据?我总是假定(从未检查过)LINQ上下文给我的基于外键的数据访问是最好的，但是看到这些额外的查询，我不再那么确定了!

将在今天晚些时候公布第二部分执行的速度(这是孟买的一个长周末，但我们正在努力完成)

结束编辑

第三编辑

(我正在考虑从web服务器到客户端的响应，因为所有的计算/抓取/绑定等都应该考虑在内。)

方法一:6.85秒(从3个表调用，然后使用c#将其转换为视图模型)

public IEnumerable<service_visit_tb> GetAllServiceVisits()
{
    var _visits = _db.service_visit_tbs;
    _db.Log = new DebuggerWriter();
    return _visits.AsEnumerable();
}
public ActionResult Index()
{
    var _retailclients = _cr.GetRetailClientNames().ToArray();
    var _corporateclients = _cr.GetCorporateClientNames().ToArray();
    var _visits = _db.GetAllServiceVisits();
    List<ServiceVisitViewModel> _temp = new List<ServiceVisitViewModel>();
    foreach (service_visit_tb v in _visits)
    {
        _temp.Add(new ServiceVisitViewModel { service_visit = v, client = (v.client_type ? _corporateclients.Where(p => p.id == v.client_id).First().name : _retailclients.Where(p => p.id == v.client_id).First().name) });
    //}
    return View(_temp);
}

方法二:8.59秒(从3个表调用，然后使用LINQ对视图模型进行强制转换)

public IEnumerable<service_visit_tb> GetAllServiceVisits()
{
    var _visits = _db.service_visit_tbs;
    _db.Log = new DebuggerWriter();
    return _visits.AsEnumerable();
}
public ActionResult Index()
{
    var _retailclients = _cr.GetRetailClientNames().ToArray();
    var _corporateclients = _cr.GetCorporateClientNames().ToArray();
    var _visits = _db.GetAllServiceVisits();
    var _temp = _visits.Select(o => new ServiceVisitViewModel
    {
        service_visit = o,
        client = (o.client_type ? _corporateclients.Where(p => p.id == o.client_id).First().name : _retailclients.Where(p => p.id == o.client_id).First().name)
    });
    return View(_temp);
}

方法三:5.76秒(所有内容在一个LINQ查询中-在数据库上执行)

public IEnumerable<ServiceVisitViewModel> GetAllServiceVisitsNew()
{
    var _visits = _db.service_visit_tbs.Select(o => new ServiceVisitViewModel
    {
        service_visit = o,
        client = (o.client_type ? _db.corporate_client_tbs.Where(c=> c.id == o.client_id).First().company_name : _db.retail_client_tbs.Where(c=> c.id == o.client_id).First().name)
    });
    _db.Log = new DebuggerWriter();
    return _visits;
}
public ActionResult Index()
{
    var _visits = _db.GetAllServiceVisitsNew();
    return View(_visits());
}

我想这就决定了。谢谢大家的帮助。我把Jon标记为正确答案，因为他在数据库端做所有事情的方法是真正成功的。非常感谢所有不辞辛苦回复的人。

结束编辑

使用LINQ . select()转换为新类型太慢了

Select语句在这里产生了巨大的差异-因为它改变了数据库中正在做的事情。(我假设_db.GetAllServiceVisits()返回IQueryable<T>)

您已经将所有零售和公司客户端获取到内存，因为您正在使用ToArray。您的Select调用将(我怀疑)然后将所有数据发送回到数据库，以便可以在那里执行Select和Where。我怀疑如果你查看SQL profiler，它将是一个非常奇怪的查询。

如果您强制所有都在客户端完成，它应该与后一种方法基本相同。这很容易做到，使用:

var _visits = _db.GetAllServiceVisits().ToList();

…但是，这意味着每次访问此页面时，都要从数据库中提取三个表的所有。我觉得那不是个好计划。

但是，如果您可以在数据库中执行所有操作，而不需要先将所有零售和企业客户端读取到内存中，那将会更好。

可能就像更改存储库方法以返回IQueryable<T>而不是IEnumerable<T>，并删除对AsEnumerable的调用一样简单。

哇。你在这里做了很多循环。循环中的每个Where在循环的每次迭代中都循环一个数组来查找一个元素。

制作客户端字典，以便快速查找。这应该会给你一个显著的速度提升:

public ActionResult Index()
{
    private ClientRepository _cr = new ClientRepository();
    var _retailclients = _cr.GetRetailClientNames().ToDictionary(c => c.id);
    var _corporateclients = _cr.GetCorporateClientNames().ToDictionary(c => c.id);
    var _visits = _db.GetAllServiceVisits();
    var _temp = _visits.Select(o => new ServiceVisitViewModel
        {
            service_visit = o,
            client = (o.client_type ? _corporateclients[o.client_id].name : _retailclients[o.client_id].name)
        }).ToArray();
    return View(_temp);
}
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