Use Entity Framework Select Single Row. Entity Framework did not generate sql statement right?

Question

I'm using Entity Framework as my data provider. And there is one specific table did not generate sql statement right. While I have passed query condition, but the Entity Framework still generate sql statement for the whole table.

The Code is like this:

public IList<Device> GetDeviceByNodeId(string nodeId)
        => GetModels(device => device.DeviceNodeId == nodeId).ToList();

public virtual IEnumerable<T> GetModels(Func<T, bool> exp)
        => EntitySet.Where(exp);

And the generated sql statement is like :

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]

Did I use linq the wrong way ?

what is type of EntitySet?

Adil Mammadov
– Adil Mammadov

2016-05-26 10:44:52 +00:00
Commented May 26, 2016 at 10:44 — Adil Mammadov
– Adil Mammadov, Commented May 26, 2016 at 10:44

Community · Accepted Answer · 2017-05-23 12:15:53Z

3

It is because you are using a function, and not an expression.

Remember that IQueryables are also IEnumerables, so you are really calling Enumerable.Where, not Queryable.Where. This will cause Entity Framework to execute the query and filter the results in memory.

Change your method signature from:

public virtual IEnumerable<T> GetModels(Func<T, bool> exp)

to

public virtual IEnumerable<T> GetModels(Expression<Func<T, bool>> exp)

See this post for more information about the differences between Expressions and Functions.

edited May 23, 2017 at 12:15

CommunityBot

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answered May 26, 2016 at 10:51

iggymoran

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1 Comment

Murray Foxcroft Over a year ago

No problem. Mark it as the answer please.

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