Lets say we have 3 tables, Users, Products, Purchases. There is a view that needs to display the purchases made by a user.

I could lookup the data required by doing:

from p in DBSet<Purchases>.Include("User").Include("Product") select p;

However, I am concern that this may have a performance impact because it will retrieve the full objects. Alternatively, I could select only the fields i need:

from p in DBSet<Purchases>.Include("User").Include("Product") select new SimplePurchaseInfo() { UserName = p.User.name, Userid = p.User.Id, ProductName = p.Product.Name ... etc };

So my question is: Whats the best practice in doing this?

== EDIT

Thanks for all the replies.

[QUESTION 1]: I want to know whether all views should work with flat ViewModels with very specific data for that view, or should the ViewModels contain the entity objects.

Real example: User reviews Products

var query = from dr in productRepository.FindAllReviews()
            where dr.User.UserId = 'userid'
            select dr;
string sql = ((ObjectQuery)query).ToTraceString();

SELECT [Extent1].[ProductId] AS [ProductId], 
       [Extent1].[Comment] AS [Comment], 
       [Extent1].[CreatedTime] AS [CreatedTime], 
       [Extent1].[Id] AS [Id], 
       [Extent1].[Rating] AS [Rating], 
       [Extent1].[UserId] AS [UserId], 
       [Extent3].[CreatedTime] AS [CreatedTime1], 
       [Extent3].[CreatorId] AS [CreatorId], 
       [Extent3].[Description] AS [Description], 
       [Extent3].[Id] AS [Id1], 
       [Extent3].[Name] AS [Name], 
       [Extent3].[Price] AS [Price], 
       [Extent3].[Rating] AS [Rating1], 
       [Extent3].[ShopId] AS [ShopId], 
       [Extent3].[Thumbnail] AS [Thumbnail], 
       [Extent3].[Creator_UserId] AS [Creator_UserId], 
       [Extent4].[Comment] AS [Comment1], 
       [Extent4].[DateCreated] AS [DateCreated], 
       [Extent4].[DateLastActivity] AS [DateLastActivity], 
       [Extent4].[DateLastLogin] AS [DateLastLogin], 
       [Extent4].[DateLastPasswordChange] AS [DateLastPasswordChange], 
       [Extent4].[Email] AS [Email], 
       [Extent4].[Enabled] AS [Enabled], 
       [Extent4].[PasswordHash] AS [PasswordHash], 
       [Extent4].[PasswordSalt] AS [PasswordSalt], 
       [Extent4].[ScreenName] AS [ScreenName], 
       [Extent4].[Thumbnail] AS [Thumbnail1], 
       [Extent4].[UserId] AS [UserId1], 
       [Extent4].[UserName] AS [UserName]
       FROM    [ProductReviews] AS [Extent1]
       INNER JOIN [Users] AS [Extent2] ON [Extent1].[UserId] = [Extent2].[UserId]
       LEFT OUTER JOIN [Products] AS [Extent3] ON [Extent1].[ProductId] = [Extent3].[Id]
       LEFT OUTER JOIN [Users] AS [Extent4] ON [Extent1].[UserId] = [Extent4].[UserId]
       WHERE N'615005822' = [Extent2].[UserId]

or

from d in productRepository.FindAllProducts()
from dr in d.ProductReviews
where dr.User.UserId == 'userid'
orderby dr.CreatedTime
select new ProductReviewInfo()
       {
           product = new SimpleProductInfo() { Id = d.Id, Name = d.Name, Thumbnail = d.Thumbnail, Rating = d.Rating },
           Rating = dr.Rating,
           Comment = dr.Comment,
           UserId = dr.UserId,
           UserScreenName = dr.User.ScreenName,
           UserThumbnail = dr.User.Thumbnail,
           CreateTime = dr.CreatedTime
       };

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Name] AS [Name], 
[Extent1].[Thumbnail] AS [Thumbnail], 
[Extent1].[Rating] AS [Rating], 
[Extent2].[Rating] AS [Rating1], 
[Extent2].[Comment] AS [Comment], 
[Extent2].[UserId] AS [UserId], 
[Extent4].[ScreenName] AS [ScreenName], 
[Extent4].[Thumbnail] AS [Thumbnail1], 
[Extent2].[CreatedTime] AS [CreatedTime]
FROM    [Products] AS [Extent1]
INNER JOIN [ProductReviews] AS [Extent2] ON [Extent1].[Id] = [Extent2].[ProductId]
INNER JOIN [Users] AS [Extent3] ON [Extent2].[UserId] = [Extent3].[UserId]
LEFT OUTER JOIN [Users] AS [Extent4] ON [Extent2].[UserId] = [Extent4].[UserId]
WHERE N'userid' = [Extent3].[UserId]
ORDER BY [Extent2].[CreatedTime] ASC

[QUESTION 2]: Whats with the ugly outer joins?