To save multiple DB calls, and since it is from the same table, I'm looking for one of the fields in my linq query to return an object with 2 fields that are IEnumerable.
I wrote some pseudeocode here that should illustrate what I'm trying to do, but its not valid Linq code. Anyone know how to make this work? (Fred & Joe will both be IEnumerable)
var c = from jobs in model.jobView
select jobs.JobID, jobs.NameID, new
{
Fred = from j in model.jobView
select jobs.Field1,
Joe = from k in model.jobView
select jobs.Field2
};
You want to create an anonymous type and then create another anonymous type within it.
I am guessing there is a typo in your two collections where you use j and k, but select with jobs
var c = from jobs in model.jobView
select new
{
jobs.JobID,
jobs.NameID,
TwoObjects = new
{
Fred = from j in model.jobView
select jobs.Field1,
Joe = from k in model.jobView
select jobs.Field2
}
};
Related
I have 2 queries that work, I was hoping to combine them to reduce the database calls.
var locations = from l in db.Locations
where l.LocationID.Equals(TagID)
select l;
I do the above because I need l.Name, but is there a way to take the above results and put them into the query below?
articles = from a in db.Articles
where
(
from l in a.Locations
where l.LocationID.Equals(TagID)
select l
).Any()
select a;
Will I actually be reducing any database calls here?
This seems a bit complicated because Locations appears to be a multi-value property of Articles and you want to only load the correct one. According to this answer to a similar question you need to use a select to return them separately in one go so e.g.
var articles = from a in db.Articles
select new {
Article = a,
Location = a.Locations.Where(l => l.LocationId == TagId)
};
First failed attempt using join:
var articlesAndLocations = from a in db.Articles
join l in a.Locations
on l.LocationID equals TagID
select new { Article = a, Location = l };
(I usually use the other LINQ syntax though so apologies if I've done something stupid there.)
Could you not use the Include() method here to pull in the locations which are associated with each article, then select both the article and location object? or the properties you need from each.
The include method will ensure that you don't need to dip into the db twice, but will allow you to access properties on related entities.
You would need to use a contains method on an IEnumerable I believe, something like this:
var tagIdList = new List() { TagID };
var articles = from a in db.Articles.Include("Locations")
where tagIdList.Contains(from l in a.Locations select l.LocationID)
select new { a, a.Locations.Name };
(Untested)
I'm kind of new to LINQ and I'm trying to represent the following query in LINQ to Entities:
Select * from Cotations CT1
where CT1.CotationID = iCot_ID and
Revision =
(select max(revision)
from Cotations CT2
where CT1.CotationID = CT2.Cotation)
where iCot_ID is an external parameter, and Cotations is my entity set.
Better yet, how can I represent this as an association between two entities?
If I have the following entities:
MasterLog:
--cotationID
Cotation:
--Cotationid
--Revision key,
and for each MasterLog I want to have an association with Cotation based only on CotationID where Revision is max for that cotation (as in above query)
Thanks.
Lukasz
I think you have overcomplicated your query. The below should do it.
int iCot_ID = 0;
var query = (
from c in context.Coalation
.Where(x=>x.Cotationid == iCot_ID)
.OrderByDesc(x=>x.Revision)
)
.FirstOrDefault();
I don't quite understand the second half of your question. Please take some time and further explain what you would like to do with MasterLog.
Here is a guess:
var cQuery = (
from c in context.Coalation
group c by g.Revision into g
orderby g.Revision descending
select g.First()
);
var mQuery = (
from m in MasterLog
join c in cQuery
on m.cotationID equals c.Cotationid
where
m.Cotationid==iCot_ID
select new {
MasterLog = m,
Cotation = c
}
);
I am trying to write a linq query that will only return certain columns from my entity object into a list object.
Below is my code which produces an error(can't implicitly convert a generic list of anonymous types to a generic list of type TBLPROMOTION):
IQueryable<TBLPROMOTION> matches = webStoreContext.TBLPROMOTION.Include("TBLSTORE").Include("LKPROMOTIONTYPE");
List<TBLPROMOTION> promotionInfo = null;
promotionInfo = (from p in matches
orderby p.PROMOTION_NM descending
select new { p.EFFECTIVE_DT, p.EXPIRE_DT, p.IS_ACTIVE,
p.PROMOTION_DESC, p.PROMOTION_ID, p.PROMOTION_NM }).ToList();
What would be the best way to accomplish this. I do not want to do a "select p" in this case and return all the columns associated with the query.
thanks in advance,
Billy
Can't you do var promotionInfo = () and get a list of anonymous types?
Okay, basically you can not cast an Anonymous type to a known type like TBLPROMOTION.
ofcourse, you can say var promotionInfo = and then get an IEnumerable<{Anonymoustype}> and use that to do, what you were wanting to do with promotionInfo.
Also, personally I prefer the Fluent version of a linq query, easy on the eyes, good programming diet, at least for me :)
var promotionInfo = matches
.OrderByDescending( p => p.PROMOTION_NM)
.Select( p => new { p.EFFECTIVE_DT,
p.EXPIRE_DT,
p.IS_ACTIVE,
p.PROMOTION_DESC,
p.PROMOTION_ID,
p.PROMOTION_NM})
.ToList();
If you're moving from a L2E query to a Type already defined, you may need a step between. I haven't tried to compile this but something like:
List<TBLPROMOTION> promotions = new List<TBLPROMOTION>();
var results = from p in matches
orderby p.PROMOTION_NM descending
select new
{
p.EFFECTIVE_DT,
p.EXPIRE_DT,
p.IS_ACTIVE,
p.PROMOTION_DESC,
p.PROMOTION_ID,
p.PROMOTION_NM
};
foreach (var v in results)
{
promotions.Add(new TBLPROMOTION(v.EFFECTIVE_DT, v.EXPIRE_DT, v.IS_ACTIVE,
v.PROMOTION_DESC, v.PROMOTION_ID, v.PROMOTION_NM));
}
Based on the comment below, you might try something like:
foreach(var v in results)
{
TBLPROMOTION temp = new TBLPROMOTION();
temp.EFFECTIVE_DT = v.EFFECTIVE_DT;
temp.EXPIRE_DT = v.EXPIRE_DT;
temp.IS_ACTIVE = v.IS_ACTIVE
// Assign Other Properties
promotions.Add(temp);
}
.......
Sorry: Just read the addition to the top.
Are you sure that none of the fields you're leaving out (instead of saying "select p") are required for a TBLPROMOTION object? Also, sense your TBLPROMOTION object is going to have properties (and therefore memory allocated) for those skipped fields, why not just use an annonymous type or set up a helper class that contains only your needed properties?
#Billy, following code worked for me.
List<TBLPROMOTION> promotionInfo =
(from p in matches
orderby p.PROMOTION_NM descending
select new TBLPROMOTION(p.EFFECTIVE_DT, p.EXPIRE_DT, p.IS_ACTIVE,
p.PROMOTION_DESC, p.PROMOTION_ID, p.PROMOTION_NM)
).ToList();
did you try
select new TBLPROMOTION {.....
instead of
select new {.....
List<TBLPROMOTION> promotionInfo = null;
promotionInfo = (from p in matches
orderby p.PROMOTION_NM descending
select new TBLPROMOTION { COL1 = p.EFFECTIVE_DT, COL2 = p.EXPIRE_DT, COL3 = p.IS_ACTIVE... }).ToList();
Where COL1, COL2, ... are the names of the properties on TBLPROMOTION you wish you populate.
If you want a subset of the table you have 2 options:
#Fredou mentioned select new TBLPROMOTION{...}
other way is to create a custom DTO which has the exact properties & select them instead like:
List promotionInfo = ...
select new TBLPROMOTION_DTO{
Effective_dt = ...
}
HTH
In another posting: Does Linq-To-Sql support composable queries there was discussion on how to compose/concat where clauses dynamically. This appears to be done with an "AND" (i.e. the first where clause and the second where clause are joined by an AND). What I am wondering is if there is a way to compose Linq queries with an OR.
Example:
var people = from p in Person
where p.age < 18
select p
var otherPeople = from p in people
where p.firstName equals "Daniel"
select p
This gives people with a first name of "Daniel" and that are under 18. I'm looking for the syntax to join these to find people who have a first name of "Daniel" or are under 18.
Note: I am using ADO.net Data Services so I do not have .Contains() available to me.
EDIT: The Union Suggestion (by Garry Shutler) is exactly what I am looking for functionality-wise. I did run into two possible issues with it:
It looks like it would make multiple database hits if I was to do a third condition (union seems to take an IEnumerable as its parameter) - I was hoping to build up multiple AND and OR statements in code and then execute one request.
Union is not supported by ADO.Net Data Services (very disappointing)
Is what you want as simple as:
var people = from p in Person
where p.age < 18 || p.firstName == "Daniel"
select p;
or have you just given a simple example?
In which case you can use:
var under18 = from p in Person
where p.age < 18
select p;
var daniels = from p in Person
where p.firstName == "Daniel"
select p;
var combined = under18.Union(daniels);
LinqToSql may be intelligent enough to convert that to an OR but I'm not so sure.
What about using PredicateBuilder by Joe Albahari?
var predicate = PredicateBuilder.False<Person>();
predicate = predicate.Or(p => p.age < 18);
predicate = predicate.Or(p => p.firstName == "Daniel");
var query = Person.Where(predicate);
The predicate option is the way to go. The Union option DOES NOT build good sql. Reference http://social.msdn.microsoft.com/forums/en-US/linqprojectgeneral/thread/925b245d-5529-4a64-8cd4-4bc83ee6fe7a/
I wrote about how to achieve queries which search for a key value within a set on my blog .
Here are the relevant links.
Contains Operations in ADO.NET Data Services Part I
Contains Operations in ADO.NET Data Services Part II
Using this , you can write queries which look like this
//The set in which we have to search for a match
List<string> citiesIWillVisit = new List<string>() {"London","Berlin","Prague"};
var customersAround = nwContext.Customers
.IsIn<Customers>(citiesIWillVisit, c=> c.City);
foreach (Customers localCustomer in customersAround) {
System.Console.WriteLine(localCustomer.ContactName);
}
I am new to LINQ. I am trying to find the rows that does not exists in the second data table.
report_list and benchmark both type are : DataTable. Both these datatables are being populated using OleDbCommand,OleDbDataAdapter. I am getting an error "Specified cast is not valid." in foreach ... loop. I would appreciate your help.
var result = from a in report_list.AsEnumerable()
where !(from b in benchmark.AsEnumerable()
select b.Field<int>("bench_id")
)
.Contains(a.Field<int>("BenchmarkID"))
select a;
foreach (var c in result)
{
Console.WriteLine(c.Field<string>("Name"));
}
I don't know if I understood your question. Are you trying to get the items that exists in the first table but not in the second?
var first = new string[] { "b", "c" };
var second = new string[] { "a", "c" };
//find the itens that exist in "first" but not in "second"
var q = from f in first
where !second.Contains(f)
select f;
foreach (var s in q) {
Console.WriteLine(s);
}
//Prints:
//b
I suggest you to make the inner query first, once it does not depend on the outer record.
From a in report_list
Group Join b in benchmark On a.bench_id Equals b.bench_id Into g = Group
Where g.Count = 0
Select a
Note that this is VB syntax.
My suspicion is that one of the fields you are comparing is not an integer in the database. I believe that the invalid cast exception is being thrown by one of the Field<int>() calls since that is one of the three different exceptions that this method can throw. See docs here.
Perhaps use the .Except() extension to get the set difference of the two sets?
(from b in benchmark.AsEnumerable()
select new { id = b.Field<int>("bench_id")}).Except(
from a in report_list.AsEnumerable()
select new {id = a.Field<int>("BenchmarkID")})
Not actually sure of the precise syntax, but that should work by taking the ids in benchmark, and then removing all equivalent ids in report_list, leaving only the ids that don't match. (I hope this is the order you were after...)
Note: This is also assuming that the above issue mentioned by tvanfosson isn't also a problem