使用过滤器对象的 Linq where 子句

Posted 2023-04-12

【中文标题】使用过滤器对象的 Linq where 子句

【英文标题】：Linq where clause using filter object

【发布时间】：2018-03-10 05:01:23

【问题描述】：

我有一块 Linq 在我的 web 控制器中查询一个 EntityFramework 上下文并返回结果，如下所示：

[HttpGet]
public IActionResult GetRoutingRules()

     var query = (from rr in _context.RoutingRules
          join dest in _context.RoutingZones on rr.DestinationZoneId equals dest.ZoneId
          join origin in _context.RoutingZones on rr.OriginZoneId equals origin.ZoneId
          join hub in _context.RoutingHub on rr.HubId equals hub.HubId
          select new RoutingRulesDto(rr)  DestinationZoneName = dest.ZoneName, OriginZoneName = origin.ZoneName, HubName = hub.HubName );

     return Ok(query);

我想要一个采用“过滤器”对象的新方法，我可以在其中缩小上述结果的范围。我的过滤器对象如下所示：

public class RoutingSearchFilterDto

     public int BrandId  get; set; 
     public int? ServiceType  get; set; 
     public long? OriginZoneId  get; set; 
     public long? DestinationZoneId  get; set; 
     public int? RuleRanking  get; set; 
     public bool? IsRuleActive  get; set; 

需要在这个类中设置的最少信息是 BrandId。所有其他属性都是过滤器中的选项。

我需要编写一个新的控制器方法来利用它，例如：

[HttpPost("filtered")]
public IActionResult GetFilteredRoutingRules([FromBody] RoutingSearchFilterDto filter)

    ...

如何对可能为空的属性进行 linq 查询？本质上，动态查询取决于过滤器对象中设置的属性。

注意：我希望这会影响 EF 运行的 select 语句，而不仅仅是让 EF 获取所有数据，然后过滤数据集 - 这样做的目的是使 db 调用更高效。

过滤器对象可能在 BrandId = 1、IsRuleActive = 1 的地方发送。同样，它可能是 BrandId = 1、ServiceType = 3（因此 IsRuleActive 为 null，因此不应在 linq where 子句中）。

我试过了：

var param = (Expression.Parameter(typeof(RoutingRules), "rr"));

Expression combinedExpr = null;
if (filter.BrandId != null)

    var exp = Expression.Equal(Expression.Property(param, "BrandId"), Expression.Constant(filter.BrandId));
    combinedExpr = exp;


if (filter.DestinationZoneId != null)

    var exp = Expression.Equal(Expression.Property(param, "DestinationZoneId"), Expression.Constant(filter.DestinationZoneId));
    combinedExpr = (combinedExpr == null ? exp : Expression.AndAlso(combinedExpr, exp));


if (filter.OriginZoneId != null)

    var exp = Expression.Equal(Expression.Property(param, "OriginZoneId"), Expression.Constant(filter.OriginZoneId));
    combinedExpr = (combinedExpr == null ? exp : Expression.AndAlso(combinedExpr, exp));


if (filter.EshopServiceType != null)

    var exp = Expression.Equal(Expression.Property(param, "EshopServiceType"), Expression.Constant(filter.EshopServiceType));
    combinedExpr = (combinedExpr == null ? exp : Expression.AndAlso(combinedExpr, exp));


if (filter.IsRuleActive != null)

    var exp = Expression.Equal(Expression.Property(param, "IsRuleActive"), Expression.Constant(filter.IsRuleActive, typeof(bool?)));
    combinedExpr = (combinedExpr == null ? exp : Expression.AndAlso(combinedExpr, exp));


if (filter.RuleRanking != null)

    var exp = Expression.Equal(Expression.Property(param, "RuleRanking"), Expression.Constant(filter.RuleRanking));
    combinedExpr = (combinedExpr == null ? exp : Expression.AndAlso(combinedExpr, exp));


if (combinedExpr == null)
    combinedExpr = Expression.Default(typeof(bool));

var compiled = Expression.Lambda<Func<RoutingRules, bool>>(combinedExpr, param).Compile();


var results = (from rr in _context.RoutingRules.Where(compiled)
                join dest in _context.RoutingZones on rr.DestinationZoneId equals dest.ZoneId
                join origin in _context.RoutingZones on rr.OriginZoneId equals origin.ZoneId
                join hub in _context.RoutingHub on rr.HubId equals hub.HubId
                where rr.BrandId == 21
                select new RoutingRulesDto(rr)  DestinationZoneName = dest.ZoneName, OriginZoneName = origin.ZoneName, HubName = hub.HubName );

但是Where子句并没有应用到生成的Sql上，好像是把所有记录拉回来，然后应用到内存中的where，这不是我需要的。

提前感谢您的任何指点！

【问题讨论】：

你没有在任何地方使用编译后的表达式。

【参考方案1】：

您可以为此构建一个表达式树，但您是否考虑过：

IQueryable<...> query = ...;

if (routingSearchFilter.ServiceType != null)
  query = query.Where(e => e.ServiceType == routingSearchFilter.ServiceType);

if (...) 
   query = query.Where(....);

EF 引擎足够聪明，可以组合 Where 子句（当然还有 AND）。

编辑：

不清楚您是要过滤连接的结果还是只过滤第一个表。在那种情况下，它会继续像

var result = (from rr in query
          join dest in _context.RoutingZones on rr.DestinationZoneId equals dest.ZoneId
          join ...
          select new RoutingRulesDto(rr) .... ).ToSometing();

但我对 RoutingRulesDto(rr) 构造函数参数有点警惕。

【讨论】：

更加简单易懂。您将逐步构建查询，并且在您开始迭代项目之前不会执行它。 EF 将创建正确的 where 子句，它不会获取所有数据并将其过滤到内存中。

对不起，让我澄清一下 - 这个解决方案非常适合动态地将 WHERE 子句添加到 sql 中，但我已经失去了使用这种格式加入的能力。生成的 sql 应该类似于“SELECT t1.a,t1.b,t2.a FROM table1 t1 JOIN table2 t2 ON t2.Id = t1.FkId WHERE ”。上面的解决方案给出了除了连接之外的所有内容。

好的，伙计们 - 弄清楚如何使用以下代码填充其他字段（没有连接）：IQueryable query = _context.RoutingRules.Include(x => x.Hub).Include( y => y.DestinationZone).Include(z => z.OriginZone);

【参考方案2】：

如果您使用 LINQ 的 fluent API，您可以有条件地添加 Where 子句。

var query = _content.RoutingRules.Where(r => r.BrandId == filter.BrandId);
if (filter.OriginZoneId != null) 
    query = query.Where(r => r.OriginZoneId == filter.OriginZoneId);

if (filter.EshopServiceType != null) 
    query = query.Where(r => r.EshopServiceType == filter.EshopServiceType);

// etc...
var result = query.ToArray();

【参考方案3】：

我的最终解决方案是黑白的，这就是我最后得到的：

[HttpPost("filtered")]
public IActionResult GetFilteredRoutingRules([FromBody] RoutingSearchFilterDto filter)

    // Query to be build on the routing rules table.
    IQueryable<RoutingRules> query = _context.RoutingRules;

    // Populate the linked foreign key entities.
    query.Include(x => x.Hub).Include(y => y.DestinationZone).Include(z => z.OriginZone);

    // Build dynamic where statements.
    if (filter.BrandId != null)
        query = query.Where(r => r.BrandId == filter.BrandId);

    if (filter.OriginZoneId != null)            
        query = query.Where(r => r.OriginZoneId == filter.OriginZoneId);

    if (filter.DestinationZoneId != null)
        query = query.Where(r => r.DestinationZoneId == filter.DestinationZoneId);

    if (filter.IsRuleActive != null)
        query = query.Where(r => r.IsRuleActive == filter.IsRuleActive);

    if (filter.RuleRanking != null)
        query = query.Where(r => r.RuleRanking == filter.RuleRanking);

    // If you want to add paging:
    query = query.Skip(filter.PageSize * filter.PageNumber).Take(filter.PageSize);

    // Perform select on the table and map the results.
    var result = query.Select(r => new RoutingRulesDto
    
        RoutingRuleId = r.RoutingRuleId,
        BrandId = r.BrandId,
        LastMileCarrierCode = r.LastMileCarrierCode,
        CashOnDelivery = r.CashOnDelivery,
        CreationTime = r.CreationTime,
        CurrencyCode = r.CurrencyCode,
        CurrencyDescription = Enum.Parse(typeof(Enumerations.CurrencyCode), r.CurrencyCode),
        DestinationZoneId = r.DestinationZoneId,
        EddFromDay = r.EddFromDay,
        EddToDay = r.EddToDay,
        ServiceType = r.ServiceType,
        ServiceTypeName = Enum.Parse(typeof(Enumerations.ServiceType), r.EshopServiceType),
        IsPickUpAvailable = r.IsPickUpAvailable,
        LastUpdateTime = r.LastUpdateTime,
        LastUpdateUser = r.LastUpdateUser,
        OriginZoneId = r.OriginZoneId,
        RuleRanking = r.RuleRanking,
        SignOnDelivery = r.SignOnDelivery,
        TermsOfDelivery = r.TermsOfDelivery,
        TermsOfDeliveryName = Enum.Parse(typeof(Enumerations.TermsOfDelivery), r.TermsOfDelivery),
        ValueOfGoods = r.ValueOfGoods,
        WeightLowerLimit = r.WeightLowerLimit,
        WeightUpperLimit = r.WeightUpperLimit,
        FirstMileCarrierCode = r.FirstMileCarrierCode,
        HubId = r.HubId,
        IsInsuranceAvailable = r.IsInsuranceAvailable,
        IsRuleActive = r.IsRuleActive,
        HubName = r.Hub.HubName,
        DestinationZoneName = r.DestinationZone.ZoneName,
        OriginZoneName = r.OriginZone.ZoneName,
    );

    // The SQL produced includes the joins and where clauses as well as only 
    // selecting the column names that are required in the flattened return object.

    return Ok(result);

感谢大家的帮助！