Currently learning Linq to Entity. I been successful, but came stumped with the orderby clause and its use with multiple tables.
var query = from k in contxt.pages.Include("keywords")
where k.ID == vals.pageId select k;
My understanding with the code above is it creates an inner join where ID is equal to pageId.
So what I am having a difficult time visualizing is how I would perform an orderby on both tables?
I would like to sort on both tables.
I have tried:
var query = from k in contxt.pages.Include("keywords") where k.ID == vals.pageId orderby k.keywords.**?** select k;
The question mark is not supposed to be there. I am showing that the column that I would like to sort by isn't there. Trying this k.Kegwords. doesn't show the column.
I would write a SQL query as follows:
string query = "SELECT pages.page, pages.title, pages.descp, keywords.keyword
FROM pages INNER JOIN keywords ON pages.ID = keywords.pageID
ORDER BY keywords.sort, pages.page";
pages and keywords have a 1 to many relationship, which FK keywords.
Thank you,
deDogs
Here you go.
var result = (from x in pages
join y in keywords on x.ID equals y.pageID
orderby y.sort, x.page
select new
{
x.Page,
x.title,
x.descp,
y.keyword
});
Related
Below is my ERD and sample data. Note, I'm using Entity Framework and Code first to control my database.
For the project named Vacation, return all the DISTINCT users who have a "true" value in UserBooleanAttributes table for either the Parents or Teens rows defined in the UserAttributes table.
Here is my current attempt:
var myQuery =
from P in context.Projects
join UA in context.UserAttributes on P.ProjectID equals UA.ProjectID
join UBA in context.UserBooleanAttributes on UA.UserAttributeID equals UBA.UserAttributeID
join U in context.Users on UBA.UserID equals U.UserID
where P.ProjectID == 1
where UBA.Value == true
where (UA.UserAttributeID == 1 || UA.UserAttributeID == 2)
select new { uba = U };
This returns 6 users, with e#acme.org being listed twice. Is there a LINQ way of returning distinct values? I suppose I could convert this to a list then filter, but I'd rather have the Database do the work.
I'd rather avoid using lambda expressions if possible. Once again, I want the database to do the work, and not have to write code to union/intersect result groups.
I'm having problems running a LINQ query between two tables and returning an answer set that doesen't match.
TB_AvailableProducts
-Prod_ID
-Name
....
TB_Purchases
-Cust_ID
-Prod_ID
Is there a way to get all distinct products that a customer has not purchased by using 1 LINQ query, or do I have to be doing two separate queries, 1 for all products and 1 for purchased products, and compare the two?
This query will return all products, which do not have related record in purchases table.
int customerID = 1;
var query = from ap in context.TB_AvailableProducts
join p in context.TB_Purchases.Where(x => x.Cust_ID == customerID)
on ap.Prod_ID equals p.Prod_ID into g
where !g.Any()
select ap;
I don't think you need Distinct here if you don't have duplicated records in your products table.
Generated SQL query will look like:
SELECT ap.Prod_ID, ap.Name
FROM TB_AvailableProducts AS ap
WHERE NOT EXISTS (SELECT
1 AS C1
FROM TB_Purchases AS p
WHERE (1 = p.Cust_ID) AND (ap.Prod_ID = p.Prod_ID)
)
I am trying to write a linq to get data from many to many tables.
Here are the tables
Products (ID,Name,Description)
Products_Items (ID,ProductID,Description)
ProductsNeeds (ID,Name)
ProductsItems_Needs (ItemID,NeedsID)
This is the t-sql query
select gPro.Name,gProItems.ShortDescription,gProItems.Description,gNeeds.Name
from Products gPro
join Products_Items gProItems on gPro.ID = gProItems.ProductID
join ProductsItems_Needs gProNeeds on gProNeeds.ItemID = gProItems.ID
join ProductsNeeds gNeeds on gNeeds.ID = gProNeeds.NeedsID
where gProItems.ID = 1
this is the linq
var q = from p in objM.Products
join gpItems in objM.Products_Items on p.ID equals gpItems.ProductID
from needs in gpItems.ProductsNeeds
where gpItems.ID == 1
select p;
This query returns (Products) and it has the Produts_Items but it has not the ProductsNeeds.
What modifications should I do in order each Products_items to have the ProductsNeeds?
Thanks
Finally I found the solution.
The change was that instead of returning Products it returns Product_Items.
var q = from pItems in objM.Products_Items
join p in objM.Products on pItems.ID equals p.ID into joinedProducts
from p in joinedProducts.DefaultIfEmpty()
from needs in pItems.ProductsNeeds
where pItems.ID == 1
select pItems;
I want to achieve the following in Linq to Entities:
Get all Enquires that have no Application or the Application has a status != 4 (Completed)
select e.*
from Enquiry enq
left outer join Application app
on enq.enquiryid = app.enquiryid
where app.Status <> 4 or app.enquiryid is null
Has anyone done this before without using DefaultIfEmpty(), which is not supported by Linq to Entities?
I'm trying to add a filter to an IQueryable query like this:
IQueryable<Enquiry> query = Context.EnquirySet;
query = (from e in query
where e.Applications.DefaultIfEmpty()
.Where(app=>app.Status != 4).Count() >= 1
select e);
Thanks
Mark
In EF 4.0+, LEFT JOIN syntax is a little different and presents a crazy quirk:
var query = from c1 in db.Category
join c2 in db.Category on c1.CategoryID equals c2.ParentCategoryID
into ChildCategory
from cc in ChildCategory.DefaultIfEmpty()
select new CategoryObject
{
CategoryID = c1.CategoryID,
ChildName = cc.CategoryName
}
If you capture the execution of this query in SQL Server Profiler, you will see that it does indeed perform a LEFT OUTER JOIN. HOWEVER, if you have multiple LEFT JOIN ("Group Join") clauses in your Linq-to-Entity query, I have found that the self-join clause MAY actually execute as in INNER JOIN - EVEN IF THE ABOVE SYNTAX IS USED!
The resolution to that? As crazy and, according to MS, wrong as it sounds, I resolved this by changing the order of the join clauses. If the self-referencing LEFT JOIN clause was the 1st Linq Group Join, SQL Profiler reported an INNER JOIN. If the self-referencing LEFT JOIN clause was the LAST Linq Group Join, SQL Profiler reported an LEFT JOIN.
Do this:
IQueryable<Enquiry> query = Context.EnquirySet;
query = (from e in query
where (!e.Applications.Any())
|| e.Applications.Any(app => app.Status != 4)
select e);
I don't find LINQ's handling of the problem of what would be an "outer join" in SQL "goofy" at all. The key to understanding it is to think in terms of an object graph with nullable properties rather than a tabular result set.
Any() maps to EXISTS in SQL, so it's far more efficient than Count() in some cases.
Thanks guys for your help. I went for this option in the end but your solutions have helped broaden my knowledge.
IQueryable<Enquiry> query = Context.EnquirySet;
query = query.Except(from e in query
from a in e.Applications
where a.Status == 4
select e);
Because of Linq's goofy (read non-standard) way of handling outers, you have to use DefaultIfEmpty().
What you'll do is run your Linq-To-Entities query into two IEnumerables, then LEFT Join them using DefaultIfEmpty(). It may look something like:
IQueryable enq = Enquiry.Select();
IQueryable app = Application.Select();
var x = from e in enq
join a in app on e.enquiryid equals a.enquiryid
into ae
where e.Status != 4
from appEnq in ae.DefaultIfEmpty()
select e.*;
Just because you can't do it with Linq-To-Entities doesn't mean you can't do it with raw Linq.
(Note: before anyone downvotes me ... yes, I know there are more elegant ways to do this. I'm just trying to make it understandable. It's the concept that's important, right?)
Another thing to consider, if you directly reference any properties in your where clause from a left-joined group (using the into syntax) without checking for null, Entity Framework will still convert your LEFT JOIN into an INNER JOIN.
To avoid this, filter on the "from x in leftJoinedExtent" part of your query like so:
var y = from parent in thing
join child in subthing on parent.ID equals child.ParentID into childTemp
from childLJ in childTemp.Where(c => c.Visible == true).DefaultIfEmpty()
where parent.ID == 123
select new {
ParentID = parent.ID,
ChildID = childLJ.ID
};
ChildID in the anonymous type will be a nullable type and the query this generates will be a LEFT JOIN.
I have the following Linq statement:
(from order in Orders.AsEnumerable()
join component in Components.AsEnumerable()
on order.ORDER_ID equals component.ORDER_ID
join detail in Detailss.AsEnumerable()
on component.RESULT_ID equals detail.RESULT_ID
where orderRestrict.ORDER_MNEMONIC == "MyOrderText"
select new
{
Mnemonic = detail.TEST_MNEMONIC,
OrderID = component.ORDER_ID,
SeqNumber = component.SEQ_NUM
}).ToList()
I expect this to put out the following query:
select *
from Orders ord (NoLock)
join Component comp (NoLock)
on ord .ORDER_ID = comp.ORDER_ID
join Details detail (NoLock)
on comp.RESULT_TEST_NUM = detail .RESULT_TEST_NUM
where res.ORDER_MNEMONIC = 'MyOrderText'
but instead I get 3 seperate queries that select all rows from the tables. I am guessing that Linq is then filtering the values because I do get the correct values in the end.
The problem is that it takes WAY WAY too long because it is pulling down all the rows from all three tables.
Any ideas how I can fix that?
Remove the .AsEnumerable()s from the query as these are preventing the entire query being evaluated on the server.