LINQ Select First

问题:

Hi I have this bit of linq code

var fp = lnq.attaches.First(a => a.sysid == sysid).name;

When profiled it generates the following t-sql

SELECT TOP (1) [t0].[sysid], [t0].[name], [t0].[att_size], [t0].[cid], [t0].[flags], [t0].[contents] 
FROM [lntmuser].[attach] AS [t0]

The way I look at it, it is returning like a select *, which will cause the query to perform a table scan rather then use an index. Bad for performance.

How could I select just the name column, like:

SELECT TOP (1)[t0].[name] FROM [lntmuser].[attach] AS [t0]

Thanks in advance

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Edit: Broken Glasses Solution profiles as desired

SELECT TOP (1) [t0].[name]
FROM [lntmuser].[attach] AS [t0]
WHERE [t0].[sysid] = @p0

回答1:

Project to the name property before using First():

var fp = lnq.attaches.Where(a => a.sysid == sysid)
                     .Select(a => a.name)
                     .First();

This doesn't change the use of an index though - for that your Where clause is responsible (in your initial query the lambda you passed to First()). Both queries benefit from an index on the name column, the second one is just faster because only one column value has to be materialized.