c# - Entity Framework使用Where方法查询单行记录,但生成的SQL语句没有Where子句是为什么?
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问题描述
问 题
在使用ENtityFramework查询数据的时候,其中有一个表,即使在Where方法中传入了查询条件,生成的SQL语句中始终不带Where子句,请问这是为什么?
调用栈:
public IList<Device> GetDeviceByNodeId(string nodeId)
=> GetModels(device => device.DeviceNodeId == nodeId).ToList();
public virtual IEnumerable<T> GetModels(Func<T, bool> exp)
=> EntitySet.Where(exp);
生成的SQL语句:
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[DeviceTypeId] AS [DeviceTypeId],
[Extent1].[OriginalDeviceId] AS [OriginalDeviceId],
[Extent1].[DeviceCode] AS [DeviceCode],
[Extent1].[StatCode] AS [StatCode],
[Extent1].[DevicePassword] AS [DevicePassword],
[Extent1].[DeviceModuleGuid] AS [DeviceModuleGuid],
[Extent1].[DeviceNodeId] AS [DeviceNodeId],
[Extent1].[FirmwareSetId] AS [FirmwareSetId],
[Extent1].[ProjectId] AS [ProjectId],
[Extent1].[StartTime] AS [StartTime],
[Extent1].[PreEndTime] AS [PreEndTime],
[Extent1].[EndTime] AS [EndTime],
[Extent1].[Status] AS [Status],
[Extent1].[CameraId] AS [CameraId],
[Extent1].[DomainId] AS [DomainId],
[Extent1].[CreateDateTime] AS [CreateDateTime],
[Extent1].[CreateUserId] AS [CreateUserId],
[Extent1].[LastUpdateDateTime] AS [LastUpdateDateTime],
[Extent1].[LastUpdateUserId] AS [LastUpdateUserId],
[Extent1].[IsDeleted] AS [IsDeleted],
[Extent1].[IsEnabled] AS [IsEnabled]
FROM [dbo].[Devices] AS [Extent1]
其他同样的方法:
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[FirmwareSetName] AS [FirmwareSetName],
[Extent1].[CreateDateTime] AS [CreateDateTime],
[Extent1].[CreateUserId] AS [CreateUserId],
[Extent1].[LastUpdateDateTime] AS [LastUpdateDateTime],
[Extent1].[LastUpdateUserId] AS [LastUpdateUserId],
[Extent1].[IsDeleted] AS [IsDeleted],
[Extent1].[IsEnabled] AS [IsEnabled]
FROM [dbo].[FirmwareSets] AS [Extent1]
WHERE [Extent1].[Id] = @EntityKeyValue1
-- EntityKeyValue1: '6c36fddf-d3d9-416b-84df-cd849006eef1' (Type = Guid, IsNullable = false)
解决方案
把参数换成Expression<Func<T, bool>>
public virtual IEnumerable<T> GetModels(Expression<Func<T, bool>> exp)
如果参数是Func<T, bool>,则查询所有数据,筛选是在内存中进行的。
Expression<Func<T, bool>> 筛选是在数据库中进行的。
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