Linq and EF4.
I have this Linq query in query syntax I would like convert into query method.
Are you able to do it? I tried more tha 2 hours without success :-(
Thanks for your time
CmsContent myContentObj = (from cnt in context.CmsContents
from categoy in cnt.CmsCategories
where categoy.CategoryId == myCurrentCategoryId && cnt.ContentId == myCurrentContentId
select cnt).Single();
My original answer selected the wrong item. It's a bit more complicated than what I had (which Ani has posted). Here's what I believe is an equivalent query however and should perform better:
CmsContent myContentObj =
context.CmsContents
.Where(cnt => cnt.ContentId == myCurrentId
&& cnt.CmsCategories
.Any(categoy => categoy.CategoryId == myCurrentCategoryId))
.Single();
Here is a non-direct translation that I believe performs the same task in much less code:
var myContentObj = context.CmsContents.Single(
x => x.ContentId == myCurrentContentId &&
x.CmsCategories.Any(y => y.CategoryId == myCurrentCategoryId)
);
Here's how the C# compiler actually does it, with some help from .NET Reflector to verify:
var myContentObj = context
.CmsContents
.SelectMany(cnt => cnt.CmsCategories,
(cnt, categoy) => new { cnt, categoy })
.Where(a => a.categoy.CategoryId == myCurrentCategoryId
&& a.cnt.ContentId == myCurrentContentId)
.Select(a => a.cnt)
.Single();
Essentially, the 'nested' from clauses results in a SelectMany call with a transparent identifier (an anonymous-type instance holding the 'parent' cnt and the 'child' categoy). The Where filter is applied on the anonymous-type instance, and then we do another Select projection to get back the 'parent'. The Single call was always 'outside' the query expression of course, so it should be obvious how that fits in.
For more information, I suggest reading Jon Skeet's article How query expressions work.
Related
I've got some IQueryables I would like to OR together. My understanding is chaining them together using Where results in ANDing them together (though my understanding may be faulty.)
Here's an example of a query I would like to OR together, in lieu of using all the chained Where clauses:
var query = query.Where(x => x.Value == 1)
.Where(x => x.Name == name);
Instead of that, I'm looking for something like:
var query = query.Where(x => x.Value == 1)
.Or(x => x.Name == name)
.Or(x => x.SomeOtherValue == something else)
.Or(x => x.AChildObject.Items.Where(item => item.SomeValue == yet something else));
...in my case there are probably 10 or items I'd need to chain together like above.
I've been looking over posts like this one and I suppose I could use a series of || statements to chain things together, but am not sure if that's the way to go. It could get very hard to read.
In researching this online I'm running into meaty articles on PredicateBuilders and the like. I'm not an expert on LINQ by any means and I was hoping for some guidance?
It looks like that you can just use OR operator.
var query = query.Where(x => x.Value == 1
|| x.Name == name)
|| x => x.SomeOtherValue == something else)
|| x => x.AChildObject.Items.Where(item => item.SomeValue == yet something else))
You can also use Union or Concat if the data being combined from different sources, see Linq union usage?
I have the following linq-to-entities query with 2 joined tables that I would like to add pagination to:
IQueryable<ProductInventory> data = from inventory in objContext.ProductInventory
join variant in objContext.Variants
on inventory.VariantId equals variant.id
where inventory.ProductId == productId
where inventory.StoreId == storeId
orderby variant.SortOrder
select inventory;
I realize I need to use the .Join() extension method and then call .OrderBy().Skip().Take() to do this, I am just gettting tripped up on the syntax of Join() and can't seem to find any examples (either online or in books).
NOTE: The reason I am joining the tables is to do the sorting. If there is a better way to sort based on a value in a related table than join, please include it in your answer.
2 Possible Solutions
I guess this one is just a matter of readability, but both of these will work and are semantically identical.
1
IQueryable<ProductInventory> data = objContext.ProductInventory
.Where(y => y.ProductId == productId)
.Where(y => y.StoreId == storeId)
.Join(objContext.Variants,
pi => pi.VariantId,
v => v.id,
(pi, v) => new { Inventory = pi, Variant = v })
.OrderBy(y => y.Variant.SortOrder)
.Skip(skip)
.Take(take)
.Select(x => x.Inventory);
2
var query = from inventory in objContext.ProductInventory
where inventory.ProductId == productId
where inventory.StoreId == storeId
join variant in objContext.Variants
on inventory.VariantId equals variant.id
orderby variant.SortOrder
select inventory;
var paged = query.Skip(skip).Take(take);
Kudos to Khumesh and Pravin for helping with this. Thanks to the rest for contributing.
Define the join in your mapping, and then use it. You really don't get anything by using the Join method - instead, use the Include method. It's much nicer.
var data = objContext.ProductInventory.Include("Variant")
.Where(i => i.ProductId == productId && i.StoreId == storeId)
.OrderBy(j => j.Variant.SortOrder)
.Skip(x)
.Take(y);
Add following line to your query
var pagedQuery = data.Skip(PageIndex * PageSize).Take(PageSize);
The data variable is IQueryable, so you can put add skip & take method on it. And if you have relationship between Product & Variant, you donot really require to have join explicitly, you can refer the variant something like this
IQueryable<ProductInventory> data =
from inventory in objContext.ProductInventory
where inventory.ProductId == productId && inventory.StoreId == storeId
orderby inventory.variant.SortOrder
select new()
{
property1 = inventory.Variant.VariantId,
//rest of the properties go here
}
pagedQuery = data.Skip(PageIndex * PageSize).Take(PageSize);
My answer here based on the answer that is marked as true
but here I add a new best practice of the code above
var data= (from c in db.Categorie.AsQueryable().Join(db.CategoryMap,
cat=> cat.CategoryId, catmap => catmap.ChildCategoryId,
cat, catmap) => new { Category = cat, CategoryMap = catmap })
select (c => c.Category)
this is the best practice to use the Linq to entity because when you add AsQueryable() to your code; system will converts a generic System.Collections.Generic.IEnumerable to a generic System.Linq.IQueryable which is better for .Net engine to build this query at run time
thank you Mr. Khumesh Kumawat
You would simply use your Skip(itemsInPage * pageNo).Take(itemsInPage) to do paging.
I have a set of unique DateTimes (without time portion) that the user can select from the user interface. This is not only a range like "LastWeek" or "LastMonth". The user can selcet every single day he wants.
What might be the best way to Linq-query in EntityFramework for matching results? I have a table Foo with an Attribute CreatedAt, which stores information with time portion. Of course I dont want to check the CreatedAt-Property on client side, SqlServer should do the job for me.
I think it should be someting like:
var query = _entities.Foo.Where(x => x.UserID == user.ID);
if (selectedDates.IsNullOrEmpty() == false)
query = query.Where(x => x.CreatedAt 'IsIn' selectedDates);
or:
foreach (var date in selectedDates)
query = query.Where(x => x.CreatedAt.Year == date.Year && x.Month == date.Month && x.Day == date.Month) //but of course here I have the problem that I have to use the 'Or'-Operator, not 'And'.
How can I accomplish this?
You can use EntityFunctions.TruncateTime() to perform a truncation of the date on the server. Then something along the lines of this should work.
query = query.Where(x => selectedDates.Contains(EntityFunctions.TruncateTime(x));
You can call the Contains extension method on selectedDates. Entity Framework 4.0 will understand this and will translate it to an IN operator in SQL:
if (selectedDates.IsNullOrEmpty() == false)
query = query.Where(x => selectedDates.Contains(x.CreatedAt));
Try query = query.Where(x => selectedDates.Contains(x.CreatedAt));
I have read over a bunch of different topics on this, but i havent found what I am looking for.
I have an EF query that is this:
var query = this.ObjectContext.Questions
.Include("AnswerKey").Include("QuestionTypes")
.Where(o => o.SurveyQuestions.Any(o2 => o2.SurveyID == id));
This was working fine until i realized that i was not taking into account my Active Flag for the AnswerKey child collection. In other words, this query should load all questions that have a parent surveyid of 3(which it does)but only load AnswerKeys that have an active flag of true.
I have tried this:
var query = this.ObjectContext.AnswerKey
.Include("Questions.QuestionTypes")
.Where(ak =>
ak.Active == true &&
ak.Questions.SurveyQuestions.Any(sq => sq.SurveyID == 3) &&
ak.Questions.Active == true)
.AsEnumerable()
.Select(ak => ak.Questions).AsQueryable();
But it returns 1 question for each answerkey. So if a question has 4 answer it shows up 4 times...
How can i do this?
You could just use Distinct() at the end to filter out the duplicates:
.AsEnumerable()
.Select(ak => ak.Questions)
.Distinct()
.AsQueryable();
Brokenglass I will try your suggestion. And give you the credit if it works..
I also found this here after following another link on SO... and this appears to work as well but i need to verify it in my app.
Currently, I have the following LINQ queries. How can I merge the two queries into one. Basically, write a LINQ query to bring back the results I'd get from
IEnumerable<int> deltaList = people2010.Except(allPeople);
except in a single query.
var people2010 = Contacts.Where(x => x.Contractors
.Any(d => d.ContractorsStatusTrackings
.Any(date => date.StatusDate.Year >= 2010)))
.Select(x => x.ContactID);
var allPeople = Contacts.Where(x => x.Contractors
.Any(m => m.ContactID == x.ContactID))
.Select(x=> x.ContactID);
Thanks!
Why can you not just do Except as you are doing? Don't forget that your people2010 and allPeople variables are just queries - they're not the data. Why not just use them as they are?
If that's not acceptable for some reason, please give us more information - such as whether this is in LINQ to Object, LINQ to SQL etc, and what's wrong with just using Except.
It sounds like you're just looking for a more elegant way to write your query. I believe that this is a more elegant way to write your combined queries:
var deltaList =
from contact in Contacts
let contractors = contact.Contractors
where contractors.Any(ctor => ctor.ContractorStatusTrackings
.Any(date => date.StatusDate.Year >= 2010))
&& !contractors.Any(m => m.ContactID == contact.ContactID)
select contact.ContactID