实体框架性能连接与导航属性

Question

I am trying to understand why is join in my case faster than statement which use navigation property. I have two queries.

First with navigation property :

          var result = (from users in context.MetricBloodPreasure
                orderby users.User.LastName, users.User.FirstName
                select new
                {
                    UserName = users.User.LastName + ", " + users.User.FirstName,
                    Date = users.DateOfValue,
                }).ToList();

Generatet sql :

SELECT 
    [Project1].[C1] AS [C1], 
    [Project1].[C2] AS [C2], 
    [Project1].[DateOfValue] AS [DateOfValue]
    FROM ( SELECT 
        [Extent1].[DateOfValue] AS [DateOfValue], 
        [Extent2].[FirstName] AS [FirstName], 
        [Extent2].[LastName] AS [LastName], 
        1 AS [C1], 
        CASE WHEN ([Extent2].[LastName] IS NULL) THEN N'' ELSE [Extent2].[LastName] END + N', ' + CASE WHEN ([Extent2].[FirstName] IS NULL) THEN N'' ELSE [Extent2].[FirstName] END AS [C2]
        FROM  [dbo].[MetricBloodPreasure] AS [Extent1]
        INNER JOIN [dbo].[User] AS [Extent2] ON [Extent1].[UserId] = [Extent2].[Id]
    )  AS [Project1]
    ORDER BY [Project1].[LastName] ASC, [Project1].[FirstName] ASC

Second with join:

var result1 = (from u in context.User
                orderby u.LastName, u.FirstName
                join us in context.MetricBloodPreasure
                    on u.Id equals us.UserId into users
                from s in users
                select new
                {
                    UserName = s.User.LastName + ", " + s.User.FirstName,
                    Date = s.DateOfValue,
                }).ToList();

Generated sql:

SELECT 
    1 AS [C1], 
    CASE WHEN ([Extent1].[LastName] IS NULL) THEN N'' ELSE [Extent1].[LastName] END + N', ' + CASE WHEN ([Extent1].[FirstName] IS NULL) THEN N'' ELSE [Extent1].[FirstName] END AS [C2], 
    [Extent2].[DateOfValue] AS [DateOfValue]
    FROM  [dbo].[User] AS [Extent1]
    INNER JOIN [dbo].[MetricBloodPreasure] AS [Extent2] ON ([Extent1].[Id] = [Extent2].[UserId]) AND ([Extent2].[UserId] = [Extent1].[Id])

Before running first query, call var user = context.User.FirstOrDefault(); because I think open connection to database take some time.

Results : Navigation property query : 00:00:00.6719646 Join query : 00:00:00.4941169

Looking at results it seems that Linq queries that use joins instead of navigation properties are faster. Is that true or I'm doing something wrong ?

Answer 1

To get a better insight into what it is doing you should get the raw SQL and you can check out the execution plan yourself.

To do this, you can either use SQL Profiler to see what query is being run, or you can log the SQL query itself by doing something like this before you run your query:

context.Database.Log = s => System.Diagnostics.Debug.WriteLine(s);

Also doing a simple benchmark like you did by running each once isn't going to necessarily be reliable. You'll want to run it multiple times and average things out. You should also run them in the opposite order to see if that changes things as well.