I'm a bit stuck on this. Basically I want to do something like the following SQL query in LINQ to SQL:
select Image from dbo.Employee where ID in(Select ID from dbo.Department where IsActive=1)
Any help would be gratefully received.
Thanks.
You can force the point with a subquery as in the question #IswantoSan links to (how to do subquery in LINQ) but, without knowing more about your entity relationships, why wouldn't simply use a join here?
from e in Employees
join d in Departments on e.ID equals d.ID
where d.IsActive
select e.Image
select Image from dbo.Employee
.Where(u =>
dbo.Employee
.Where(x => u.IsActive = 1)
.Select(x.ID)
)
Is the query that will work for you.
Related
can anybody help me to convert this SQL query to LINQ code in MVC? I need to return a list. The DB context entity is: _dbContext.
select distinct table1.AIG_ID, table1.GMT_NAME, table1.AIG_Number
from table1 left join table2 on table1.AIG_ID = table2.AIG_ID**
var data=(from item in db.table1 join
item1 in db.table2 on item.AIG_ID equals item1.AIG_ID
select new {item.AIG_ID ,item.GMT_NAME ,item.AIG_Number }).GroupBy(a=>a.AIG_ID).select(a=>a.FirstOrDefault()).ToList();
I write this part for your distinct in sql
GroupBy(a=>a.AIG_ID).select(a=>a.FirstOrDefault())
I have a Linq queries that have tables join and couple of tables inner join together. Sometimes I got an error from the query when table is empty. What I trying to do is I am tryting to get a value from table even if other table is empty.
Thanks in Advance.
You need to do left join
Assuming left join between customer and order table.
var query =
from customer in dc.Customers
from order
in dc.Orders
.Where(o => customer.CustomerId == o.CustomerId)
.DefaultIfEmpty()
select new { Customer = customer, Order = order }
Also refer below link
http://forums.asp.net/t/1792428.aspx/1
I have a query based on the following T SQL:
select t1.field1
t2.field1,
t2.field2,
t3.field1,
t3.field2
from t1 left outer join t2 on t1.t2key = t2.id
left outer join t3 on t1.t3key = t3.id
In Linq to Entities the query takes the form
var query = db.context.t1.include(“t2”).include(“t3”);
The table t1 has an unusual structure in that fields t2key and t3key are nullable. The nullable fields are preventing me from filtering by any of the t2 or t3 fields.
The only way out I can see so far is to return the results as a database view before I perform the filtering. Or is there another approach I should be taking here?
For what it's worth I ended up using Linq in the end. If anyone else is in the same boat this is the syntax that got around the nullable issue:
query = query.Where(x => x.t1field != null ? x.t1field.t3field.Contains(model.propvalue) : false).Select(x => x);
I need the fields in 1 table contingent on 1 property matching rows in another table.
I can write this query in SQL with a subquery as such:
SELECT *
FROM Table1
WHERE Property1 IN
(
SELECT Property1
FROM Table2
WHERE Property0 = 1
)
But I read here that it's less complicated and just as easy to write with a join, which I did. However, so far I'm unable to return just Table1 as I'd like since I'm using a join, which if I'm not mistaken, requires me to create this anonymous type, as below. What I did here works (I created another object with the same properties of Table1 I need), but I can't help thinking there's a better way to do this.
Table1.Join(Table2, t1 => t1.Property1, t2 => t2.Property1, (t1, t2) => new
{
t1.Property1,
t1.Property2,
t1.Property3
})
.Select(ob => new UnnecessaryObject
{
Property1 = ob.Property1,
Property2 = ob.Property2,
Property3 = ob.Property3
}
I also tried just creating a Table1 in the .Select part, but I got an error about explicit construction not being allowed.
Just to clarify, I'd like to be able to return the IQueryable of type Table1, which it seems like I ought to be able to do without having to create UnnecessaryObject...but I'm still pretty new to LINQ, so I'd appreciate any help you can offer. Thanks in advance.
You could just do:
from t1 in table1
join t2 in table2 on t1.property1 equals t2.property1
select t1;
That would return a collection of table1 objects. This assumes from your example table1 is a collection of table1 objects and table2 is a collection of table2 objects.
The best translation of your original query I can come up with is:
from item in context.Table1
where context.Table2
.Where(x => x.Property0 == 0)
.Any(x => x.Property1 == item.Property1)
select item
This selects all items from Table1, where there's an item with matching Property1 and Property0 == 0 from Table2
It can also be solved with a join indeed. To get an efficient join, you need to have a relation between the two tables. Then you can do something like assuming the relation is called RelatedItems:
from item in context.Table1
join relatedItem in item.RelatedItems
on item.Property1 equals relatedItem.Property
where relatedItem.Property0 == 0
select item
This is equivalent to the SQL:
SELECT *
FROM Table1
JOIN Table2 ON Table1.Property1 = Table2.Property1
WHERE Table2.Property0 = 0
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.