Question

我正在进行一些EF查询优化。为了更好地理解查询性能，我正在研究生成的SQL，有些条件让我发疯：

WHERE (cast(1 as bit) <> cast(0 as bit))...

我无法想象一个案例，当这个条件评估为假时。也：

CASE WHEN ([Extent9].[Id] IS NULL) THEN...

显然，[Extent9]。[Id]表示相应表格中的主键列，当然不能是NULL。

为什么SQL中存在这些条件？这是LINQ查询文本，如果它可以帮助回答问题：

var query = _context
    .Objects
    .Where(o => o.DatawareVersionId == _datawareId);
    .SelectMany(t => t.ComplexSubTasks)
    .Where(st => st.Variant.Order.CurrentAlgoVersion != null)
    .Select(st => st.Variant.Order.CurrentAlgoVersion)
    .OfType<MonitoringAlgoVersion>()
    .Where(version => version != null && version.Applicabilities.Any(applicability => applicability.SymbolicCircuitTypeId == _typeId))
    .Any());
    .Select(o => o.Group)
    .Distinct();

更新即可。整个SQL语句：

SELECT 
[Distinct1].[Id] AS [Id], 
[Distinct1].[GenericGroup] AS [GenericGroup], 
[Distinct1].[Number] AS [Number], 
[Distinct1].[Group] AS [Group]
FROM ( SELECT DISTINCT 
    [Extent2].[Id] AS [Id], 
    [Extent2].[GenericGroup] AS [GenericGroup], 
    [Extent2].[Number] AS [Number], 
    [Extent2].[Group] AS [Group]
    FROM  [dbo].[Objects] AS [Extent1]
    INNER JOIN [dbo].[ObjectGroups] AS [Extent2] ON [Extent1].[GroupId] = [Extent2].[Id]
    WHERE ([Extent1].[DatawareVersionId] = @p__linq__0) AND ( EXISTS (SELECT 
        1 AS [C1]
        FROM ( SELECT 
            [Extent9].[Id] AS [Id]
            FROM       [dbo].[Tasks] AS [Extent3]
            INNER JOIN [dbo].[SubTasks] AS [Extent4] ON [Extent3].[Id] = [Extent4].[TaskId]
            LEFT OUTER JOIN [dbo].[Variants] AS [Extent5] ON [Extent4].[VariantId] = [Extent5].[Id]
            LEFT OUTER JOIN [dbo].[Orders] AS [Extent6] ON [Extent5].[OrderId] = [Extent6].[Id]
            INNER JOIN [dbo].[AlgoVersions] AS [Extent7] ON [Extent6].[CurrentAlgoVersion] = [Extent7].[Id]
            LEFT OUTER JOIN [dbo].[Orders] AS [Extent8] ON [Extent5].[OrderId] = [Extent8].[Id]
            LEFT OUTER JOIN [dbo].[AlgoVersions] AS [Extent9] ON [Extent8].[CurrentAlgoVersion] = [Extent9].[Id]
            WHERE (cast(1 as bit) <> cast(0 as bit)) AND ([Extent1].[Id] = [Extent3].[ObjectId]) AND (CASE WHEN ([Extent9].[Id] IS NULL) THEN CAST(NULL AS varchar(1)) ELSE '10X0X' END LIKE '10X0X%')
        )  AS [Project1]
        WHERE  EXISTS (SELECT 
            1 AS [C1]
            FROM [apot].[draw_algo_versions_applicability] AS [Extent10]
            WHERE ([Project1].[Id] = [Extent10].[algo_version_id]) AND ([Extent10].[schema_type_id] = @p__linq__1)
        )
    ))
)  AS [Distinct1]

更新2 。这是实体类型，映射到AlgoVersions表：

public abstract class AlgoVersion : VersionedEntity
{           
    public virtual int OrderId { get; set; }
    public virtual Order Order { get; set; }
    public virtual bool IsErrorFixed { get; set; }
    public virtual bool IsFunctionalityExtended { get; set; }
    public virtual ObservableCollection<AlgoVersionStatus> Statuses { get; set; }
}

public class MonitoringAlgoVersion : AlgoVersion
{
    public virtual ObservableCollection<TemplateGroup> TemplateGroups { get; set; }
    public virtual ObservableCollection<MonitoringAlgoVersionApplicability> Applicabilities { get; set; }
}

其中VersionedEntity是实体的基类，其中Id和ObjectVersion（Entity和VersionedEntity都未映射到任何表格）：

public abstract class Entity
{
    public virtual int Id { get; set; }
}

public abstract class VersionedEntity : Entity
{
    public virtual byte[] ObjectVersion { get; set; }
}

Answer 1

我不确定为什么 cast(1 as bit) <> cast(0 as bit)，但有a work item in the EF backlog to remove this。我建议投票。我想这意味着它完全没用，因为该项目由RoMiller发布。它在查询中非常常见，我以前见过它。

生成的SQL查询中的奇怪条件

1 个答案: