I really love Dapper's simplicity and possibilities. I would like to use Dapper to solve common challenges I face on a day-to-day basis. These are described below.
Here is my simple model.
public class OrderItem {
public long Id { get; set; }
public Item Item { get; set; }
public Vendor Vendor { get; set; }
public Money PurchasePrice { get; set; }
public Money SellingPrice { get; set; }
}
public class Item
{
public long Id { get; set; }
public string Title { get; set; }
public Category Category { get; set; }
}
public class Category
{
public long Id { get; set; }
public string Title { get; set; }
public long? CategoryId { get; set; }
}
public class Vendor
{
public long Id { get; set; }
public string Title { get; set; }
public Money Balance { get; set; }
public string SyncValue { get; set; }
}
public struct Money
{
public string Currency { get; set; }
public double Amount { get; set; }
}
Two challenges have been stumping me.
Question 1:
Should I always create a DTO with mapping logic between DTO-Entity in cases when I have a single property difference or simple enum/struct mapping?
For example: There is my Vendor entity, that has Balance property as a struct (otherwise it could be Enum). I haven't found anything better than that solution:
public async Task<Vendor> Load(long id) {
const string query = #"
select * from [dbo].[Vendor] where [Id] = #id
";
var row = (await this._db.QueryAsync<LoadVendorRow>(query, new {id})).FirstOrDefault();
if (row == null) {
return null;
}
return row.Map();
}
In this method I have 2 overhead code:
1. I have to create LoadVendorRow as DTO object;
2. I have to write my own mapping between LoadVendorRow and Vendor:
public static class VendorMapper {
public static Vendor Map(this LoadVendorRow row) {
return new Vendor {
Id = row.Id,
Title = row.Title,
Balance = new Money() {Amount = row.Balance, Currency = "RUR"},
SyncValue = row.SyncValue
};
}
}
Perhaps you might suggest that I have to store amount & currency together and retrieve it like _db.QueryAsync<Vendor, Money, Vendor>(...)- Perhaps, you are right. In that case, what should I do if I need to store/retrive Enum (OrderStatus property)?
var order = new Order
{
Id = row.Id,
ExternalOrderId = row.ExternalOrderId,
CustomerFullName = row.CustomerFullName,
CustomerAddress = row.CustomerAddress,
CustomerPhone = row.CustomerPhone,
Note = row.Note,
CreatedAtUtc = row.CreatedAtUtc,
DeliveryPrice = row.DeliveryPrice.ToMoney(),
OrderStatus = EnumExtensions.ParseEnum<OrderStatus>(row.OrderStatus)
};
Could I make this work without my own implementations and save time?
Question 2:
What should I do if I'd like to restore data to entities which are slightly more complex than simple single level DTO? OrderItem is beautiful example. This is the technique I am using to retrieve it right now:
public async Task<IList<OrderItem>> Load(long orderId) {
const string query = #"
select [oi].*,
[i].*,
[v].*,
[c].*
from [dbo].[OrderItem] [oi]
join [dbo].[Item] [i]
on [oi].[ItemId] = [i].[Id]
join [dbo].[Category] [c]
on [i].[CategoryId] = [c].[Id]
join [dbo].[Vendor] [v]
on [oi].[VendorId] = [v].[Id]
where [oi].[OrderId] = #orderId
";
var rows = (await this._db.QueryAsync<LoadOrderItemRow, LoadItemRow, LoadVendorRow, LoadCategoryRow, OrderItem>(query, this.Map, new { orderId }));
return rows.ToList();
}
As you can see, my question 1 problem forces me write custom mappers and DTO for every entity in the hierarchy. That's my mapper:
private OrderItem Map(LoadOrderItemRow row, LoadItemRow item, LoadVendorRow vendor, LoadCategoryRow category) {
return new OrderItem {
Id = row.Id,
Item = item.Map(category),
Vendor = vendor.Map(),
PurchasePrice = row.PurchasePrice.ToMoney(),
SellingPrice = row.SellingPrice.ToMoney()
};
}
There are lots of mappers that I'd like to eliminate to prevent unnecessary work.
Is there a clean way to retrive & map Order
entity with relative properties like Vendor, Item, Category etc)
You are not showing your Order entity but I'll take your OrderItem as an example and show you that you don't need a mapping tool for the specific problem (as quoted). You can retrieve the OrderItems along with the Item and Vendor info of each by doing the following:
var sql = #"
select oi.*, i.*, v.*
from OrderItem
inner join Item i on i.Id = oi.ItemId
left join Vendor v on v.Id = oi.VendorId
left join Category c on c.Id = i.CategoryId";
var items = connection.Query<OrderItem, Item, Vendor, Category, OrderItem>(sql,
(oi,i,v,c)=>
{
oi.Item=i;oi.Item.Category=c;oi.Vendor=v;
oi.Vendor.Balance = new Money { Amount = v.Amount, Currency = v.Currency};
return oi;
});
NOTE: The use of left join and adjust it accordingly based on your table structure.
I'm not sure I understand your question a 100%. And the fact that no one has attempted to answer it yet, leads me to believe that I'm not alone when I say it might be a little confusing.
You mention that you love Dapper's functionality, but I don't see you using it in your examples. Is it that you want to develop an alternative to Dapper? Or that you don't know how to use Dapper in your code?
In any case, here's a link to Dapper's code base for your review:
https://github.com/StackExchange/dapper-dot-net
Hoping that you'd be able to clarify your questions, I'm looking forward to your reply.
Related
I have referenced numerous questions on this site related to calculated fields and ViewModels, but I can't seem to extrapolate from examples given. I hope that laying out a specific scenario would allow someone to pin point what I can't see. I am new to WebApp design in general. Please take that into consideration. Also, if I've left off any relevant information, please let me know and I will update the question.
Here is the scenario:
I have a complex query that is spanning multiple tables to return data used in calculations. Specifically, I store units for a recipe converted to a base unit and then convert the quantity to the units specified by the user.
I am using AutoMapper to map from entities to ViewModels and vice versa, but I am not sure how to handle the calculated values. Especially with the nested ViewModel Collection thrown into the mix.
Option 1
Do I return an autonomous set of data? Like the following... and then somehow use AutoMapper to do the mapping? Perhaps I would need to do the mapping manually, which I haven't found a solid example which includes nested ViewModels. At this point, I'm not even sure if the following code handles the nested collection correctly for the autonomous data.
var userId = User.Identity.GetUserId();
var recipes = from u in db.Users.Where(u => u.Id == userId)
from c in db.Categories
from r in db.Recipes
join ur in db.UserRecipes.Where(u => u.UserId == userId) on r.Id equals ur.RecipeId
join mus in db.MeasUnitSystems on ur.RecipeYieldUnitSysId equals mus.Id
join muc in db.MeasUnitConvs on mus.Id equals muc.UnitSysId
join mu in db.MeasUnits on mus.UnitId equals mu.Id
join msy in db.MeasUnitSymbols on mu.Id equals msy.UnitId
select new
{
Id = c.Id,
ParentId = c.ParentId,
Name = c.Name,
Descr = c.Descr,
Category1 = c.Category1,
Category2 = c.Category2,
Recipes = new
{
Id = r.Id,
Title = r.Title,
Descr = r.Descr,
Yield = String.Format("{0} {1}", ((r.Yield * muc.UnitBaseConvDiv / muc.UnitBaseConvMult) - muc.UnitBaseConvOffset), msy.Symbol)
}
};
Option 2
Another option that crossed my mind was to return the entities and use AutoMapper as I normally would. Then iterate through the collections and perform the calculations there. I feel like I could make this work, but it seems inefficient to me because it would result in many queries back to the database.
Option 3
???? I can't think of any other method to do this. But, please, if you have suggestions, I am more than willing to hear them.
Relevant Data
Here is the query returning the data I want in SQL Server (more or less).
declare #uid as nvarchar(128) = 'da5435ae-5198-4690-b502-ea3723a9b217'
SELECT c.[Name] as [Category]
,r.Title
,r.Descr
,(r.Yield*rmuc.UnitBaseConvDiv/rmuc.UnitBaseConvMult)-rmuc.UnitBaseConvOffset as [Yield]
,rmsy.Symbol
FROM Category as c
inner join RecipeCat as rc on c.Id = rc.CategoryId
inner join Recipe as r on rc.RecipeId = r.Id
inner join UserRecipe as ur on r.Id = ur.RecipeId and ur.UserId = #uid
inner join MeasUnitSystem as rmus on ur.RecipeYieldUnitSysId = rmus.Id
inner join MeasUnitConv as rmuc on rmus.Id = rmuc.UnitSysId
inner join MeasUnit as rmu on rmus.UnitId = rmu.Id
inner join MeasUnitSymbol as rmsy on rmu.Id = rmsy.UnitId
inner join UserUnitSymbol as ruus on rmsy.UnitId = ruus.UnitId and rmsy.SymIndex = ruus.UnitSymIndex and ruus.UserId = #uid
ViewModels
public class CategoryRecipeIndexViewModel
{
public int Id { get; set; }
public int ParentId { get; set; }
[Display(Name = "Category")]
public string Name { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
public ICollection<CategoryRecipeIndexViewModel> Category1 { get; set; }
public CategoryRecipeIndexViewModel Category2 { get; set; }
public ICollection<RecipeIndexViewModel> Recipes { get; set; }
}
public class RecipeIndexViewModel
{
public int Id { get; set; }
[Display(Name = "Recipe")]
public string Title { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
[Display(Name = "YieldUnit")]
public string Yield { get; set; }
}
UPDATE 2/10/2018
I found an answer here that does a very good job of explaining exactly what I'm looking at. Particularly under the A Better solution ? section. Mapping queries directly to my ViewModels looks like it would allow me to get my calculated values as well. Problem is, the example given is once again too simplistic.
He gives the following DTO's
public class UserDto
{
public int Id {get;set;}
public string Name {get;set;}
public UserTypeDto UserType { set; get; }
}
public class UserTypeDto
{
public int Id { set; get; }
public string Name { set; get; }
}
And does the following for mapping:
var users = dbContext.Users.Select(s => new UserDto
{
Id = s.Id,
Name = s.Name,
UserType = new UserTypeDto
{
Id = s.UserType.Id,
Name = s.UserType.Name
}
});
Now what if the UserDTO looked like this:
public class UserDto
{
public int Id {get;set;}
public string Name {get;set;}
public ICollection<UserTypeDto> UserTypes { set; get; }
}
How would the mapping be done if the UserTypes were a collection?
Update 2/13/2018
I feel I am making progress, but am currently headed in the wrong direction. I found this and came up with the following (which currently errors because of the method call in the linq query):
*Note: I removed Category2 from the ViewModel as I found it was not needed and only complicated this further.
query inside index controller method
IEnumerable<CategoryRecipeIndexViewModel> recipesVM = db.Categories
.Where(x => x.ParentId == null)
.Select(x => new CategoryRecipeIndexViewModel()
{
Id = x.Id,
ParentId = x.ParentId,
Name = x.Name,
Descr = x.Descr,
Category1 = MapCategoryRecipeIndexViewModelChildren(x.Category1),
Recipes = x.Recipes.Select(y => new RecipeIndexViewModel()
{
Id = y.Id,
Title = y.Title,
Descr = y.Descr
})
});
Recursive Method
private static IEnumerable<CategoryRecipeIndexViewModel> MapCategoryRecipeIndexViewModelChildren(ICollection<Category> categories)
{
return categories
.Select(c => new CategoryRecipeIndexViewModel
{
Id = c.Id,
ParentId = c.ParentId,
Name = c.Name,
Descr = c.Descr,
Category1 = MapCategoryRecipeIndexViewModelChildren(c.Category1),
Recipes = c.Recipes.Select(r => new RecipeIndexViewModel()
{
Id = r.Id,
Title = r.Title,
Descr = r.Descr
})
});
}
At this point, I don't even have the calculations I require, but that doesn't matter until I get this working (small steps). I quickly discovered you can't really call a method inside a Linq Query. Then a thought occurs to me, if I need to force the Linq Query to execute and then perform all the mapping on the in memory data, then I would essentially be doing the same thing as Option 2 (above), but I could perform the calculations within the ViewModel. This is the solution I will pursue and will keep everyone posted.
You have to iterate over UserType Collection and map the value to UserType dto's collection.
Use this code.
var users = dbContext.Users.Select(s => new UserDto
Id = s.Id,
Name = s.FullName,
UserType = s.UserType.Select(t => new UserTypeDto
{
Id = t.Id,
Name = t.Name
}).ToList()
Hope this will help.
I got it working! ...I think. ...Maybe. If anything, I'm querying the data, mapping it to my ViewModels and I have the calculations too. I do have additional questions, but they are a lot more specific. I will layout the solution I followed and where I think it requires work below.
I basically implemented my Option 2 from above, but instead of iterating through the collections, I just performed the calculations within the ViewModels.
Controller Method
public ActionResult Index()
{
var userId = User.Identity.GetUserId();
var recipes = db.Categories.Where(u => u.Users.Any(x => x.Id == userId))
.Include(c => c.Category1)
.Include(r => r.Recipes
.Select(u => u.UserRecipes
.Select(s => s.MeasUnitSystem.MeasUnitConv)))
.Include(r => r.Recipes
.Select(u => u.UserRecipes
.Select(s => s.MeasUnitSystem.MeasUnit.MeasUnitSymbols)));
IEnumerable<CategoryRecipeIndexViewModel> recipesVM = Mapper.Map<IEnumerable<Category>, IEnumerable<CategoryRecipeIndexViewModel>>(recipes.ToList());
return View(recipesVM);
}
View Models
public class CategoryRecipeIndexViewModel
{
public int Id { get; set; }
public int ParentId { get; set; }
[Display(Name = "Category")]
public string Name { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
public ICollection<CategoryRecipeIndexViewModel> Category1 { get; set; }
public ICollection<RecipeIndexViewModel> Recipes { get; set; }
}
public class RecipeIndexViewModel
{
public int Id { get; set; }
[Display(Name = "Recipe")]
public string Title { get; set; }
[Display(Name = "Description")]
public string Descr { get; set; }
public double Yield { get; set; }
public ICollection<UserRecipeIndexViewModel> UserRecipes { get; set; }
[Display(Name = "Yield")]
public string UserYieldUnit
{
get
{
return System.String.Format("{0} {1}", ((Yield *
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnitConv.UnitBaseConvDiv /
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnitConv.UnitBaseConvMult) -
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnitConv.UnitBaseConvOffset).ToString("n1"),
UserRecipes.FirstOrDefault().MeasUnitSystem.MeasUnit.MeasUnitSymbols.FirstOrDefault().Symbol);
}
}
}
public class UserRecipeIndexViewModel
{
public MeasUnitSystemIndexViewModel MeasUnitSystem { get; set; }
}
public class MeasUnitSystemIndexViewModel
{
public MeasUnitIndexViewModel MeasUnit { get; set; }
public MeasUnitConvIndexViewModel MeasUnitConv { get; set; }
}
public class MeasUnitIndexViewModel
{
public ICollection<MeasUnitSymbolIndexViewModel> MeasUnitSymbols { get; set; }
}
public class MeasUnitConvIndexViewModel
{
public double UnitBaseConvMult { get; set; }
public double UnitBaseConvDiv { get; set; }
public double UnitBaseConvOffset { get; set; }
}
public class MeasUnitSymbolIndexViewModel
{
public string Symbol { get; set; }
}
This appears to be working, but I know it needs some work.
For instance, the relation shown between the Recipe and UserRecipe shows one to many. In reality, if the UserRecipe were filtered by the current user, the relationship would be one to one. Also, the same goes for the MeasUnit and the MeasUnitSymbol entities. Currently, I'm relying on the FirstOrDefault of those collections to actually perform the calculations.
Also, I have seen numerous posts that state that calculations should not be done in the View Models. Except for some who say it's okay if it is only a requirement of the View.
Last I will say that paying attention to variable names within the ViewModels would have saved me some headaches. And I thought I knew how to utilize Linq Queries, but had issues with the data returned. It was easier to rely on the eager loading provided by Entity Framework to bring back the hierarchical data structure needed, versus the flat table structures I'm used to working with.
I'm still new to a lot of this and wrapping my head around some of the quirks of MVC and Entity Framework leaves me brain dead after a few hours, but I will continue to optimize and adopt better programming methods as I go.
I have Medals class, I call a service that return all Medal class fields except for the two fields ArabicName and ISOCode; Which I have to bring them from another table class "CountrysTBLs" , I made this join code:
The Medal class:
public class Medals {
public int bronze_count { get; set; }
public string country_name { get; set; }
public int gold_count { get; set; }
public string id { get; set; }
public int place { get; set; }
public int silver_count { get; set; }
public int total_count { get; set; }
public string ArabicName { get; set; } // this field not return by service
public string ISOCode { get; set; } // this field not return by service
}
The code:
var cntrs = db.CountrysTBLs.ToList();
List<Medals> objs = call_Service_Of_Medals_Without_ISOCode();
IEnumerable<Medals> query = from obj in objs
join cntry in cntrs on obj.country_name equals '%' + cntry.CommonName + '%'
select new Medals
{
ArabicName = cntry.ArabicName,
ISOCode = cntry.ISOCode,
country_name = obj.country_name,
place = obj.place,
gold_count = obj.gold_count,
silver_count = obj.silver_count,
bronze_count = obj.bronze_count,
total_count = obj.total_count
};
I get no result?!
How to fix that? Is there is any way to bring the two fields (ISOCode, ArabicName) without even use the inner join, and in same time best performance?
You want something like this to achieve LIKE functionality
List<Medals> medals = new List<Medals>();
var list = medals.Select(x => new
{
obj = x,
country = countries.FirstOrDefault(c => c.CommonName.Contains(x.country_name))
});
or something like this (if you want to just enrich each medal)
foreach (var medal in medals)
{
var country = countries.FirstOrDefault(c => c.CommonName.Contains(x.country_name));
medal.ISOCode = country.ISOCode;
medal.ArabicName = country.ArabicName;
}
Do note that this is not as performant as a Dictionary<string,Coutnry> of countries where the key is the country name, but as you need a LIKE comparison you would need to bring in a custom data structure such as Lucene index for fast lookups. But check first, if the lists are small enough, it probably won't be a problem. Otherwise, why not make the Medal.Country_Name and Country.Name the same? So you can do quick Dictionary (hashtable) lookups
I have the code below which works:
List<XXTJobTableModel> xjobs = filexxts.GroupBy(x=> x.job)
.Select(fx => new JobTableModel
{
job_no = fx.First().job,
emps = fx.GroupBy(x=>x.emp_id).Select(x => new EmployeeTableModel
{
eid = x.First().emp_id,
heds = x.GroupBy(h => h.HED).Select(h => new HEDModel
{
hed = h.First().HED,
hours = h.Sum(c => c.HOURS),
amt = h.Sum(c => c.AMOUNTRATE)
}).ToList()
}).ToList()
}).ToList();
public class JobTableModel
{
public string job_no { get; set; }
public List<EmployeeTableModel> emps { get; set; }
}
public class EmployeeTableModel
{
public string emp_id { get; set; }
public List<HEDModel> heds { get; set; }
}
public class THEDModel
{
public string hed { get; set; }
public decimal hours { get; set; }
public decimal amt { get; set; }
}
I have another List<XXTJobTableModel> yjobs already loaded from another data source. What I would like to do, if the job_no is not found in yjobs, then add the job (with employee and he data) to yjobs. If the job_no is found in yjobs, and the emp_id is not found in the Employee table for that job, then add the employee (and hed data) to that jobs. If the employee is found in that job, then just add the HED data to the employees list.
I do not have a preference if I somehow merge xjobs and yjobs or if I load the xjobs directly into the yjobs list.
thanks
Are you looking for a very concise set of LINQ statements to do this merge operation or just any solution at all? What I would do is loop through one set and use LINQ to compare each item to the other set, and add items resulting from the comparison to a third set. Problems like this you have to decompose into manageable pieces, and then recompose it into a larger solution once the smaller pieces are working. Make an attempt and if you get stuck someone on here will surely be able to fill in the blanks.
I have the following tables:
I'm using Entity Framework Database First, therefore the following entity class is generated:
public partial class Sal1 {
public string SaleID { get; set; }
public string ItemID { get; set; }
public int Quantity { get; set; }
public decimal Total { get; set; }
public virtual Item Item { get; set; }
public virtual Sale Sale { get; set; }
}
Then put the Sal1 rows into a datagrid like this:
private List<Sal1> saleItems = new List<Sal1>();
...
var query = from sa in db.Sal1
where sa.SaleID.Equals(tempSale)
select sa;
foreach(Sal1 si in query) {
saleItems.Add(si);
}
...
dgDetails.ItemsSource = saleItems;
But it turns out like this:
My question is, how should I tweak the query above so that I get the equivalent of the following SQL:
select T0.SaleID, T0.ItemID, T1.Name, T0.Quantity, T0.Total
from Sal1 T0 inner join Item T1 on T0.ItemID = T1.ItemID;
Thanks in advance.
EDIT: I seem to have found a solution, but I had to do this:
var query = from sa in db.Sal1
where sa.SaleID.Equals(tempSale)
select new { sa.SaleID, sa.ItemID, sa.Item.Name,
sa.Item.Manufacturer, sa.Quantity, sa.Total };
And I had to change the type of saleItems to object.
private List<object> saleItems = new List<object>();
Is this the best way to do it?
Just like SQL, LINQ also supports JOINs. You can read more about their syntax here. You should change your query accordingly to get your results. Instead of spoonfeeding the exact answer, I'm guiding you to a more detailed explanation, as it contains valuable information that will help you in the future too.
I'm creating a product listing for an online store. It's pretty standard stuff, a page of product thumbnails with brief details, price and a link through to full details.
I'm using a repository pattern, so I have a central data repository which gives me back tables from a SQL server. I've cut a lot of the code out for the sake of brevity, but just so you get the idea:
public class SqlProductsRepository : IProductsRepository
{
private Table<Product> productsTable;
public SqlProductsRepository(string connectionString)
{
var context = new DataContext(connectionString);
productsTable = context.GetTable<Product>();
// More tables set up here
}
public IQueryable<Product> Products
{
get { return productsTable; }
}
// More properties here
}
I have the following objects mapped to tables:
[Table(Name = "Products")]
public class Product
{
[Column(IsPrimaryKey = true)]
public string ProductCode { get; set; }
[Column]
public string Name { get; set; }
[Column]
public decimal Price { get; set; }
public List<ShopImage> Images = new List<ShopImage>();
}
[Table(Name = "Images_Products")]
public class Image_Product
{
[Column]
public int ImageID { get; set; }
[Column]
public string ProductCode { get; set; }
[Column]
public int DisplayOrder { get; set; }
}
[Table(Name = "Images")]
public class Image
{
[Column(Name = "ImageID")]
public int ImageID { get; set; }
[Column]
public bool Caption { get; set; }
}
If I perform the following query:
// 'db' is the repository (member variable of the controller class)
IQueryable<Product> products = from p in db.Products
join ip in db.Image_Product on p.ProductCode equals ip.ProductCode
where ip.DisplayOrder == 0
select p;
I get a nice IQueryable full of Product objects. However, what I want to do is populate each object's Images list property with a single Image object, with its ID set from the joined Image_Product table.
So I end up with a list of Products, each with one Image in its Images property, which has the ID of the image for that product in the database where DisplayOrder is 0.
I tried this projection, which I thought made sense:
IQueryable<Product> products = from p in db.Products
join ip in db.Image_Product on p.ProductCode equals ip.ProductCode
where ip.DisplayOrder == 0
select new Product {
ProductCode = p.ProductCode,
Price = p.Price,
Images = new List<Image> {
new Image { ImageID = ip.ImageID }
}
};
Which compiles, but throws a runtime error: Explicit construction of entity type 'xxx.Product' in query is not allowed.
Yet elsewhere in the project I do this:
var pages = from i in db.TemplatePageNavigationItems
orderby i.DisplayOrder
select new NavigationItem {
ID = i.PageID,
ParentID = i.ParentID,
Text = i.Name,
Title = i.Name,
Url = (i.Folder == null) ? "" : i.Folder
};
And get no complaints! I assume it's something to do with the first query returning an IQueryable<Product> but I'm not sure why.
Two questions really: why is this not allowed in the first situation, and what should I be doing in order to get my desired result?
As the error says, you can't construct explicit entity types (Product is just that) in your query which should return IQueryable<Product>. Your pages query will return IEnumerable<NavigationItem> and NavigationItem does not seem to be an entity type defined in the database.
You could try returning IEnumerable<Product> in your first query or define a separate type and return IEnumerable of that instead, if you need to project explicit, custom tailored instances of an object.