我有一段 Linq 查询我的网络 Controller 中的 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);
}
我想要一个新的方法,它将采用一个“过滤器”对象,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; }
}
该类最少需要设置的信息是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 Controller 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 - 这样做的目的是提高 db 调用的效率。
过滤器对象可能会发送到 BrandId = 1、IsRuleActive = 1 的位置。同样,它可能是 BrandId = 1、ServiceType = 3(因此 IsRuleActive 为空,因此不应出现在 linq where 子句中)。
我已经试过了:
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中,好像是拉回所有记录,然后应用内存中的where,这不是我需要的。
在此先感谢您的指点!!
最佳答案
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 引擎足够智能,可以组合 Where 子句(当然还有 AND)。
编辑:
不清楚您是想过滤连接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) 构造函数参数有点担心。
关于c# - 使用过滤器对象的 Linq where 子句,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46469348/